MAX16909RATE/V+T - Hytronics - Products.Express

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

�� Maxim Integrated Products 1

General Description

The MAX16909 is a 3A, current-mode, step-down con-

verter with an integrated high-side switch. The device is

designed to operate with input voltages from 3.5V to 36V

while using only 30FA quiescent current at no load. The

switching frequency is adjustable from 220kHz to 1MHz

by an external resistor and can be synchronized to an

external clock. The output voltage is pin selectable to

be 5V fixed or adjustable from 1V to 10V. The wide input

voltage range along with its ability to operate at high duty

cycle during undervoltage transients make the device

ideal for automotive and industrial applications.

The device operates in skip mode for reduced current

consumption in light-load applications. Protection features

include overcurrent limit, overvoltage, and thermal shut-

down with automatic recovery. The device also features

a power-good monitor to ease power-supply sequencing.

The device operates over the -40NC to +125NC automo-

tive temperature range, and is available in 16-pin TSSOP

and TQFN (5mm x 5mm) packages with exposed pads.

Applications

Automotive

Industrial/Military

High-Voltage Input DC-DC Converter

Point-of-Load Applications

Features

S Wide 3.5V to 36V Input Voltage Range

S 42V Input Transients Tolerance

S High Duty Cycle During Undervoltage Transients

S 5V Fixed or 1V to 10V Adjustable Output Voltage

S Integrated 3A Internal High-Side (70mI typ)

Switch

S Fast Load-Transient Response and Current-Mode

Architecture

S Adjustable Switching Frequency (220kHz to 1MHz)

S Frequency Synchronization Input

S 30µA Standby Mode Operating Current

S 5µA Typical Shutdown Current

S Overvoltage, Undervoltage, Overtemperature, and

Short-Circuit Protections

Typical Application Circuit

19-5777; Rev 0; 3/11

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part,

refer to: www.maxim-ic.com/MAX16909.related

D1 COUT

100µF

CIN2

4.7µF

RCOMP

47kIRPGOOD

10kI

RFOSC

65kI

L1

10µH VOUT

5V AT 3A

CBST

0.1µF

LX

BST

VOUT

VBIAS

OUT

VBAT

FB

VBIAS

PGOOD

FOSC

CBIAS

1µF

CCOMP2

10pF

BIAS

CCOMP1

2.7nF

COMP

FSYNC

EN

SUPSWSUP

GND

CIN1

47µF

POWER GOOD

MAX16909

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

�� Maxim Integrated Products 2

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

SUP, SUPSW, LX, EN to GND ...............................-0.3V to +42V

SUP to SUPSW .....................................................-0.3V to +0.3V

BST to GND ...........................................................-0.3V to +47V

BST to LX ...............................................................-0.3V to +6V

OUT to GND ..........................................................-0.3V to +12V

FOSC, COMP, BIAS, FSYNC, I.C., PGOOD,

FB to GND ............................................................-0.3V to +6V

LX Continuous RMS Current ...................................................4A

Output Short-Circuit Duration ....................................Continuous

Continuous Power Dissipation (TA = +70NC)

TSSOP (derate 26.1mW/oC above +70NC) .......... 2088.8mW*

TQFN (derate 28.6mW/oC above +70NC) ............ 2285.7mW*

Operating Temperature Range ........................ -40NC to +125NC

Junction Temperature .....................................................+150NC

Storage Temperature Range ............................ -65NC to +150NC

Lead Temperature (soldering, 10s) ................................+300NC

Soldering Temperature (reflow) ..................................... +260oC

TSSOP

Junction-to-Ambient Thermal Resistance (BJA) .......38.3NC/W

Junction-to-Case Thermal Resistance (BJC) .................3NC/W

TQFN

Junction-to-Ambient Thermal Resistance (BJA) ..........35NC/W

Junction-to-Case Thermal Resistance(BJC) ...............2.7NC/W

ABSOLUTE MAXIMUM RATINGS

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-

tion of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect device reliability.

PACKAGE THERMAL CHARACTERISTICS (Note 1)

ELECTRICAL CHARACTERISTICS

(VSUP = VSUPSW = 14V, VEN = 14V, RFOSC = 120kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at

TA = +25NC.)

*As per the JEDEC 51 standard (multilayer board).

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage Range VSUP,

VSUPSW 3.5 36 V

Load-Dump Event Supply

Voltage VSUP_LD tLD < 1s 42 V

Supply Current

ISUP ILOAD = 1.5A 3.5 mA

ISUP_STANDBY

Standby mode, no load, VOUT = 5V 30 60

FA

Standby mode, no load, VOUT = 5V,

TA = +25°C 30 45

Shutdown Supply Current ISHDN VEN = 0V 5 12 FA

BIAS Regulator Voltage VBIAS VSUP = VSUPSW = 6V to 36V 4.7 5 5.3 V

BIAS Undervoltage Lockout VUVBIAS VBIAS rising 2.9 3.1 3.3 V

BIAS Undervoltage-Lockout

Hysteresis 400 mV

Thermal-Shutdown Threshold +175 NC

Thermal-Shutdown Threshold

Hysteresis 15 NC

OUTPUT VOLTAGE (OUT)

Output Voltage VOUT VFB = VBIAS, normal operation 4.925 5 5.075 V

*The parametric values (min, typ, max limits) shown in the Electrical Characteristics table supersede values quoted elsewhere in this data sheet.

�� Maxim Integrated Products 3

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

ELECTRICAL CHARACTERISTICS* (continued)

(VSUP = VSUPSW = 14V, VEN = 14V, RFOSC = 120kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at

TA = +25NC.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Skip-Mode Output Voltage VOUT_SKIP No load, VFB = VBIAS 4.925 5 5.15 V

Adjustable Output Voltage

Range VOUT_ADJ FB connected to external resistive divider 1 10 V

Load Regulation VFB = VBIAS, 30mA < ILOAD < 3A 0.5 %

Line Regulation VFB = VBIAS, 6V < VSUPSW < 36V 0.02 %/V

BST Input Current IBST_ON High-side on, VBST - VLX = 5V 1.5 2.5 mA

LX Current Limit ILX (Note 2) 3.4 4.1 6 A

Skip-Mode Threshold ISKIP_TH 300 mA

Power-Switch On-Resistance RON RON measured between SUPSW and LX,

ILX = 1A, VBIAS = 5V 70 150 mI

High-Side Switch Leakage

Current VSUP = 36V, VLX = 0V, TA = +25°C 1 FA

TRANSCONDUCTANCE AMPLIFIER (COMP)

FB Input Current IFB 10 nA

FB Regulation Voltage VFB

FB connected to an external resistive

divider; 0°C < TA < +125°C 0.99 1.0 1.01 V

-40°C < TA < +125°C 0.985 1.0 1.015

FB Line Regulation DVLINE 6V < VSUP < 36V 0.02 %/V

Transconductance (from FB to

COMP) gmVFB = 1V, VBIAS = 5V (Note 2) 900 FS

Minimum On-Time tON_MIN 80 ns

Maximum Duty Cycle DCMAX

fSW = 1MHz 98 %

fSW = 220kHz 99

OSCILLATOR FREQUENCY

Oscillator Frequency RFOSC = 120kI190 220 250 kHz

EXTERNAL CLOCK INPUT (FSYNC)

FSYNC Input Current TA = +25°C 1 FA

External Input Clock Acquisition

Time tFSYNC 1 Cycles

External Input Clock Frequency (Note 2) fOSC +

10% Hz

External Input Clock

High Threshold VFSYNC_HI VFSYNC rising 1.4 V

External Input Clock

Low Threshold VFSYNC_LO VFSYNC falling 0.4 V

Soft-Start Time tSS 8.5 ms

*The parametric values (min, typ, max limits) shown in the Electrical Characteristics table supersede values quoted elsewhere in this data sheet.

�� Maxim Integrated Products 4

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

ELECTRICAL CHARACTERISTICS* (continued)

(VSUP = VSUPSW = 14V, VEN = 14V, RFOSC = 120kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at

TA = +25NC.)

Note 2: Guaranteed by design; not production tested.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

ENABLE INPUT (EN)

Enable Input-High Threshold VEN_HI 2 V

Enable Input-Low Threshold VEN_LO 0.9 V

Enable Threshold Voltage

Hysteresis VEN,HYS 0.2 V

Enable Input Current IEN TA = +25°C 1 FA

RESET

Output Overvoltage Trip

Threshold VOUT_OV 105 110 115 %VFB

PGOOD Switching Level VTH_RISING VFB rising, VPGOOD = high 93 95 97 %VFB

VTH_FALLING VFB falling, VPGOOD = low 90 92.5 95

PGOOD Debounce 10 35 60 Fs

PGOOD Output Low Voltage ISINK = 5mA 0.4 V

PGOOD Leakage Current VOUT in regulation, TA = +25NC1FA

*The parametric values (min, typ, max limits) shown in the Electrical Characteristics table supersede values quoted elsewhere in this data sheet.

�� Maxim Integrated Products 5

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Typical Operating Characteristics

(VSUP = VSUPSW = VEN = 14V, VOUT = 1.8V, R1 = 80.6kΩ, R2 = 100kΩ, TA = +25NC (Figure 4), unless otherwise noted.)

SWITCHING FREQUENCY vs. ILOAD

(1.8V/400kHz)

MAX16909 toc06

SWITCHING FREQUENCY (kHz)

391

392

393

394

395

396

397

398

399

400

390

ILOAD (A)

2.52.01.51.00.50 3.0

VIN = 14V

SWITCHING FREQUENCY vs. RFOSC

MAX16909 toc05

RFOSC (kI)

SWITCHING FREQUENCY (MHz)

1009070 8040 50 6030

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0

20 110

VIN = 14V

0.010.0010.00010 0.1

EFFICIENCY vs. LOAD CURRENT

VIN = 14V

MAX16909 toc04

LOAD CURRENT (A)

EFFICIENCY (%)

10

20

30

40

50

60

70

80

90

100

0

1.8V

3.3V

5V

8V

D1: B360B-13-F, DIODES

L1: DRA125-150-R,

COOPER BUSSMANN

EFFICIENCY vs. LOAD CURRENT

VIN = 14V

MAX16909 toc03

LOAD CURRENT (A)

EFFICIENCY (%)

0 0.5 1.51.0 2.52.0 3.0

10

20

30

40

50

60

70

80

90

100

0

DIODE: B360B-13-F FROM DIODES

INDUCTOR: DRA125-150-R,

COOPER BUSSMANN

1.8V

3.3V 5V 8V

MAX16909 toc02

VIN

VOUT

VPGOOD

5V/div

1V/div

0V

2ms/div

STARTUP INTO NO LOAD

(1.8V/400kHz)

STARTUP INTO HEAVY LOAD

(1.8V/400kHz)

MAX16909 toc01

VIN

VOUT

ILOAD

VPGOOD

5V/div

1V/div

2A/div

0V

0A

0V

2ms/div

0.6I RESISTIVE LOAD

�� Maxim Integrated Products 6

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Typical Operating Characteristics (continued)

(VSUP = VSUPSW = VEN = 14V, VOUT = 1.8V, R1 = 80.6kΩ, R2 = 100kΩ, TA = +25NC (Figure 4), unless otherwise noted.)

OUTPUT RESPONSE TO SLOW INPUT

(ILOAD = 3A)

MAX16909 toc12

VIN

VLX

VPGOOD

VOUT

5V/div

10V/div

2V/div

0V

2s/div

1.8V/400kHz

0.6I RESISTIVE LOAD

LOAD DUMP TEST (1.8V/400kHz)

MAX16909 toc11

VIN

VOUT

10V/div

2V/div

0V

10ms/div

14V

42V

UNDERVOLTAGE PULSE (1.8V/400kHz)

MAX16909 toc10

VSUPSW

VLX

ILOAD

VOUT 2V/div

5V/div

20V/div

5A/div

0A

0V

20ms/div

SUP = 5V

RESISITIVE LOAD = 0.6I

FSYNC TRANSITION FROM INTERNAL

TO EXTERNAL FREQUENCY (1.8V/400kHz)

MAX16909 toc09

VFSNC

VLX

5V/div

10V/div

0V

2µs/div

fFSYNC = 440kHz

SKIP-MODE LOAD-TRANSIENT

RESPONSE (1.8V/400kHz)

MAX16909 toc08

VOUT

AC-COUPLED

ILOAD

50mV/div

10mA/div

0A

100µs/div

VIN = 14V

PWM MODE LOAD-TRANSIENT

RESPONSE (1.8V/400kHz)

MAX16909 toc07

VOUT

AC-COUPLED

ILOAD

200mV/div

1A/div

0A

100µs/div

VIN = 14V

0.5A

�� Maxim Integrated Products 7

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Typical Operating Characteristics (continued)

(VSUP = VSUPSW = VEN = 14V, VOUT = 1.8V, R1 = 80.6kΩ, R2 = 100kΩ, TA = +25NC (Figure 4), unless otherwise noted.)

VOUT vs. SUPPLY VOLTAGE

(1.8V/400kHz)

MAX16909 toc17

SUPPLY VOLTAGE (V)

VOUT (V)

3024181260 36

ILOAD = 0A

1.76

1.77

1.78

1.79

1.80

1.81

1.82

1.83

1.84

1.85

1.75

VOUT vs. SUPPLY VOLTAGE

(1.8V/400kHz)

MAX16909 toc16

SUPPLY VOLTAGE (V)

30

24181260 36

ILOAD = 3A

VOUT (V)

1.76

1.77

1.78

1.79

1.80

1.81

1.82

1.83

1.84

1.85

1.75

VOUT vs. TEMPERATURE

(1.8V/400kHz)

VOUT (V)

1.72

1.74

1.76

1.78

1.82

1.84

1.86

1.88

1.90

1.70

MAX16909 toc15

1.80

TEMPERATURE (°C)

1109580655035205-10-25-40 125

ILOAD = 3A

ILOAD = 0A

VIN = 14V

VOUT LOAD REGULATION (1.8V/400kHz)

MAX16909 toc14

ILOAD (A)

VOUT (V)

2.52.01.51.00.5

1.76

1.77

1.78

1.79

1.80

1.81

1.82

1.83

1.84

1.85

1.75

0 3.0

VIN = 14V

MAX16909 toc13

VOUT

ILX

VPGOOD

5V/div

1V/div

2A/div

0A

0V

10ms/div

SHORT CIRCUIT TO GROUND TEST

(1.8V/400kHz)

�� Maxim Integrated Products 8

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Typical Operating Characteristics (continued)

(VSUP = VSUPSW = VEN = 14V, VOUT = 1.8V, R1 = 80.6kΩ, R2 = 100kΩ, TA = +25NC (Figure 4), unless otherwise noted.)

181612 144 6 8 1020 20

VBIAS LOAD REGULATION

(1.8V/400kHz)

MAX16909 toc18

IBIAS (mA)

VBIAS (V)

5.20

5.18

5.16

5.14

5.12

5.10

5.08

5.06

5.04

5.02

5.00

4.98

4.96

4.94

4.92

4.90

TA = 125°C

TA = -40°C

TA = 25°C

MAX16909 toc22

VOUT

VIN

VPGOOD

VLX 10V/div

2V/div

10V/div

5V/div

0V

10ms/div

LINE TRANSIENT TEST

(1.8V/400kHz)

1.8V/400kHz

0.6I LOAD

MAX16909 toc21

VOUT

VIN

VPGOOD

VLX

10V/div

2V/div

10V/div

5V/div

0V

10ms/div

DIPS AND DROP TEST

(1.8V/400kHz)

0.6I RESISTIVE LOAD

ISHDN vs. TEMPERATURE

ISHDN (µA)

4

5

6

4

MAX16909 toc20

5

TEMPERATURE (°C)

1109580655035205-10-25-40 125

VEN = 0V

ISHDN vs. SUPPLY VOLTAGE

MAX16909 toc19

SUPPLY VOLTAGE (V)

ISHDN (µA)

3831241710

2

4

6

8

10

12

14

16

18

20

0

3 45

TA = -40°C

TA = 25°C

TA = 125°C

VEN = 0V

VIN = 14V

�� Maxim Integrated Products 9

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Pin Configurations

Pin Descriptions

PIN NAME FUNCTION

TSSOP TQFN

1 15 FSYNC

Synchronization Input. The device synchronizes to an external signal applied to FSYNC.

The external clock frequency must be 10% greater than the internal clock frequency for

proper operation. Connect FSYNC to GND if the internal clock is used.

2 16 FOSC Resistor-Programmable Switching-Frequency Setting Control Input. Connect a resistor

from FOSC to GND to set the switching frequency.

3 1 PGOOD Open-Drain, Active-Low Output. PGOOD asserts when VOUT is below the 92.5% regula-

tion point. PGOOD deasserts when VOUT is above the 95% regulation point.

4 2 OUT Switch Regulator Output. OUT also provides power to the internal circuitry when the out-

put voltage of the converter is set between 3V and 5V during standby mode.

5 3 FB Feedback Input. Connect an external resistive divider from OUT to FB and GND to set

the output voltage. Connect to BIAS to set the output voltage to 5V.

6 4 COMP Error-Amplifier Output. Connect an RC network from COMP to GND for stable operation.

See the Compensation Network section for more details.

7 5 BIAS Linear Regulator Output. BIAS powers up the internal circuitry. Bypass with a 1FF

capacitor to ground.

8 6 GND Ground

9 7 BST High-Side Driver Supply. Connect a 0.1FF capacitor between LX and BST for proper

operation.

++

TSSOP

13

4

SUPSW

OUT

14

3

SUPSW

PGOOD

15

2

EN

FOSC

16

1

TOP VIEW

I.C.FSYNC

10

7

SUP

BIAS

11

6

LX

COMP

9

8

BST

GND

12

5

LX

FB

EP EP

MAX16909 MAX16909

15

16

14

13

6

5

7

OUT

COMP

8

PGOOD

SUPSW

LX

SUPSW

1 2

I.C.

4

12 11 9

FSYNC

FOSC

SUP

BST

GND

BIAS

FB LX

3

10

EN

TQFN

(5mm × 5mm)

TOP VIEW

�� Maxim Integrated Products 10

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Pin Descriptions (continued)

Internal Block Diagram

PIN NAME FUNCTION

TSSOP TQFN

10 8 SUP Voltage Supply Input. SUP powers up the internal linear regulator. Connect a minimum

4.7FF capacitor to ground.

11, 12 9, 10 LX Inductor Switching Node. Connect a Schottky diode between LX and GND.

13, 14 11, 12 SUPSW Internal High-Side Switch-Supply Input. SUPSW provides power to the internal switch.

Connect a 0.1FF decoupling capacitor and a 4.7FF ceramic capacitor to ground.

15 13 EN SUP Voltage-Compatible Enable Input. Drive EN low to disable the device. Drive EN

high to enable the device.

16 14 I.C. Internally Connected. Connect to ground for proper operation.

— — EP

Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective

power dissipation. Do not use as the only IC ground connection. EP must be connected

to GND.

MAX16909

FBSW

OUT COMP PGOOD EN

FB

SOFT-

START

SLOPE

COMP

FBOK

EAMP

HSD

AON

LOGIC

CS

REF

HVLDO

SWITCH-

OVER

OSC

PWM

SUP BIAS

BST

SUPSW

LX

GND

FSYNC FOSC

�� Maxim Integrated Products 11

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Detailed Description

The MAX16909 is a constant-frequency, current-mode,

automotive buck converter with an integrated high-side

switch. The device operates with input voltages from 3.5V

to 36V and tolerates input transients from 3.5V up to 42V.

During undervoltage events, such as cold-crank condi-

tions, the internal pass device maintains 98% duty cycle.

The switching frequency is resistor programmable from

220kHz to 1MHz to allow optimization for efficiency, noise,

and board space. A synchronization input FSYNC allows

the device to synchronize to an external clock frequency.

During light-load conditions, the device enters skip mode

for high efficiency. The 5V fixed output voltage eliminates

the need for external resistors and reduces the supply

current to 30FA. See the Internal Block Diagram for more

information.

Wide Input Voltage Range (3.5V to 36V)

The device includes two separate supply inputs, SUP

and SUPSW, specified for a wide 3.5V to 36V input

voltage range. VSUP provides power to the device and

VSUPSW provides power to the internal switch. When

the device is operating with a 3.5V input supply, certain

conditions such as cold crank can cause the voltage at

SUPSW to drop below the programmed output voltage.

As such, the device operates in a high duty-cycle mode

to maintain output regulation.

Linear Regulator Output (BIAS)

The device includes a 5V linear regulator, BIAS, that

provides power to the internal circuitry. Connect a 1FF

ceramic capacitor from BIAS to GND.

External Clock Input (FSYNC)

The device synchronizes to an external clock signal

applied at FSYNC. The signal at FSYNC must have a

10% higher frequency than the internal clock frequency

for proper synchronization.

Soft-Start

The device includes an 8.5ms fixed soft-start time for up

to 500FF capacitive load with a 3A resistive load.

Minimum On-Time

The device features a 80ns minimum on-time that

ensures proper operation at 1MHz switching frequency

and high differential voltage between the input and the

output. This feature is extremely beneficial in automo-

tive applications where the board space is limited and

the converter needs to maintain a well-regulated output

voltage using an input voltage that varies from 9V to

18V. Additionally, the device incorporates an innovative

design for fast-loop response that further ensures good

output-voltage regulation during transients.

System Enable (EN)

An enable-control input (EN) activates the device from its

low-power shutdown mode. EN is compatible with inputs

from automotive battery level down to 3.3V. The high-

voltage compatibility allows EN to be connected to SUP,

KEY/KL30, or the INH pin of a CAN transceiver.

EN turns on the internal regulator. Once VBIAS is above

the internal lockout threshold, VUVL = 3.15V (typ), the

controller activates and the output voltage ramps up

within 8.5ms.

A logic-low at EN shuts down the device. During shut-

down, the internal linear regulator and gate drivers turn

off. Shutdown is the lowest power state and reduces the

quiescent current to 5FA (typ). Drive EN high to bring the

device out of shutdown.

Overvoltage Protection

The device includes overvoltage protection circuitry that

protects the device when there is an overvoltage condi-

tion at the output. If the output voltage increases by more

than 110% of its set voltage, the device stops switching.

The device resumes regulation once the overvoltage

condition is removed.

Fast Load-Transient Response

Current-mode buck converters include an integrator

architecture and a load-line architecture. The integra-

tor architecture has large loop gain but slow transient

response. The load-line architecture has fast transient

response but low loop gain. The device features an inte-

grator architecture with innovative designs to improve

transient response. Thus, the device delivers high output-

voltage accuracy, plus the output can recover quickly

from a transient overshoot, which could damage other

on-board components during load transients.

Overload Protection

The overload protection circuitry is triggered when the

device is in current limit and VOUT is below the reset

threshold. Under these conditions the device turns the

high-side FET off for 16ms and re-enters soft-start. If the

overload condition is still present, the device repeats the

cycle.

�� Maxim Integrated Products 12

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Skip Mode/Standby Mode

During light-load operation, IINDUCTOR P 185mA, the

device enters skip mode operation. Skip mode turns off

the majority of circuitry and allows the output to drop

below regulation voltage before the switch is turned on

again. The lower the load current, the longer it takes for

the regulator to initiate a new cycle. Because the con-

verter skips unnecessary cycles and turns off the majority

of circuitry, the converter efficiency increases. When the

high-side FET stops switching for more than 50Fs, most

of the internal circuitry, including LDO, draws power from

VOUT (VOUT = 3V to 5.5V), allowing current consumption

from the battery to drop to only 30FA.

Overtemperature Protection

Thermal-overload protection limits the total power dis-

sipation in the device. When the junction temperature

exceeds +175NC (typ), an internal thermal sensor

shuts down the internal bias regulator and the step-

down converter, allowing the IC to cool. The thermal

sensor turns on the IC again after the junction tempera-

ture cools by 15NC.

Applications Information

Setting the Output Voltage

Connect FB to BIAS for a fixed 5V output voltage. To set

the output to other voltages between 1V and 10V, con-

nect a resistive divider from output (OUT) to FB to GND

(Figure 1). Calculate RFB1 (OUT to FB resistor) with the

following equation:

OUT

FB1 FB2 FB

V

R R 1

V

 

 

= −

 

 

 

 

 

where VFB = 1V (see the Electrical Characteristics table).

Internal Oscillator

The switching frequency, fSW, is set by a resistor (RFOSC)

connected from FOSC to GND. See Figure 2 to select the

correct RFOSC value for the desired switching frequency.

For example, a 400kHz switching frequency is set with

RFOSC = 65kI. Higher frequencies allow designs with

lower inductor values and less output capacitance.

Consequently, peak currents and I2R losses are lower

at higher switching frequencies, but core losses, gate

charge currents, and switching losses increase.

Inductor Selection

Three key inductor parameters must be specified for

operation with the device: inductance value (L), inductor

saturation current (ISAT), and DC resistance (RDCR). To

select inductance value, the ratio of inductor peak-to-

peak AC current to DC average current (LIR) must be

selected first. A good compromise between size and loss

is a 30% peak-to-peak ripple current to average-current

ratio (LIR = 0.3). The switching frequency, input voltage,

output voltage, and selected LIR then determine the

inductor value as follows:

OUT SUP OUT

SUP SW OUT

V (V V )

LV f I LIR

−

=

where VSUP, VOUT, and IOUT are typical values (so that

efficiency is optimum for typical conditions). The switch-

ing frequency is set by RFOSC (see the Internal Oscillator

section). The exact inductor value is not critical and can

be adjusted to make trade-offs among size, cost, efficien-

cy, and transient response requirements. Table 1 shows

a comparison between small and large inductor sizes.

Figure 1. Adjustable Output-Voltage Setting

Figure 2. Switching Frequency vs. RFOSC

RFB2

RFB1

FB

MAX16909

VOUT

SWITCHING FREQUENCY vs. RFOSC

MAX16909 toc05

RFOSC (kI)

SWITCHING FREQUENCY (MHz)

1009070 8040 50 6030

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0

20 110

VIN = 14V

�� Maxim Integrated Products 13

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

The inductor value must be chosen so that the maximum

inductor current does not reach the device’s minimum

current limit. The optimum operating point is usually

found between 25% and 35% ripple current. When pulse

skipping (FSYNC low and light loads), the inductor value

also determines the load-current value at which PFM/

PWM switchover occurs.

Find a low-loss inductor having the lowest possible

DC resistance that fits in the allotted dimensions. Most

inductor manufacturers provide inductors in standard

values, such as 1.0FH, 1.5FH, 2.2FH, 3.3FH, etc. Also

look for nonstandard values, which can provide a bet-

ter compromise in LIR across the input voltage range. If

using a swinging inductor (where the no-load inductance

decreases linearly with increasing current), evaluate

the LIR with properly scaled inductance values. For

the selected inductance value, the actual peak-to-peak

inductor ripple current (DIINDUCTOR) is defined by:

OUT SUP OUT

INDUCTOR SUP SW

V (V V )

IV f L

−

∆ = × ×

where DIINDUCTOR is in A, L is in H, and fSW is in Hz.

Ferrite cores are often the best choices, although pow-

dered iron is inexpensive and can work well at 200kHz.

The core must be large enough not to saturate at the

peak inductor current (IPEAK):

INDUCTOR

PEAK LOAD(MAX)

I

I I 2

∆

= +

Input Capacitor

The input filter capacitor reduces peak currents drawn

from the power source and reduces noise and voltage

ripple on the input caused by the circuit’s switching.

The input capacitor RMS current requirement (IRMS) is

defined by the following equation:

OUT SUP OUT

RMS LOAD(MAX) SUP

V (V V )

I I V

−

=

IRMS has a maximum value when the input voltage

equals twice the output voltage (VSUP = 2VOUT), so

IRMS(MAX) = ILOAD(MAX)/2.

Choose an input capacitor that exhibits less than +10NC

self-heating temperature rise at the RMS input current for

optimal long-term reliability.

The input-voltage ripple is composed of DVQ (caused

by the capacitor discharge) and DVESR (caused by the

equivalent series resistance (ESR) of the capacitor). Use

low-ESR ceramic capacitors with high ripple-current

capability at the input. Assume the contribution from the

ESR and capacitor discharge equal to 50%. Calculate

the input capacitance and ESR required for a specified

input-voltage ripple using the following equations:

ESR

IN L

OUT

V

ESR I

I2

∆

=∆

+

where

SUP OUT OUT

LSUP SW

(V V ) V

IV f L

− ×

∆ = × ×

and

OUT

IN Q SW

I D(1 D)

CV f

× −

=∆ ×

and

OUT

SUPSW

V

DV

=

where IOUT is the maximum output current, and D is the

duty cycle.

Output Capacitor

The output filter capacitor must have low enough ESR to

meet output ripple and load-transient requirements, yet

have high enough ESR to satisfy stability requirements.

The output capacitance must be high enough to absorb

the inductor energy while transitioning from full-load

to no-load conditions without tripping the overvoltage

fault protection. When using high-capacitance, low-ESR

capacitors, the filter capacitor’s ESR dominates the

output-voltage ripple. So the size of the output capaci-

tor depends on the maximum ESR required to meet the

output-voltage ripple (VRIPPLE(P-P)) specifications:

VRIPPLE(P-P) = ESR × ILOAD(MAX) × LIR

The actual capacitance value required relates to the

physical size needed to achieve low ESR, as well as

to the chemistry of the capacitor technology. Thus, the

capacitor is usually selected by ESR and voltage rating

rather than by capacitance value.

Table 1. Inductor Size Comparison

INDUCTOR SIZE

SMALLER LARGER

Lower price Smaller ripple

Smaller form factor Higher efficiency

Faster load response Larger fixed-frequency

range in skip mode

�� Maxim Integrated Products 14

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

When using low-capacity filter capacitors, such as

ceramic capacitors, size is usually determined by the

capacity needed to prevent voltage droop and volt-

age rise from causing problems during load transients.

Generally, once enough capacitance is added to meet

the overshoot requirement, undershoot at the rising load

edge is no longer a problem. However, low-capacity filter

capacitors typically have high-ESR zeros that can affect

the overall stability.

Rectifier Selection

The device requires an external Schottky diode recti-

fier as a freewheeling diode. Connect this rectifier close

to the device using short leads and short PCB traces.

Choose a rectifier with a voltage rating greater than the

maximum expected input voltage, VSUPSW. Use a low

forward-voltage-drop Schottky rectifier to limit the nega-

tive voltage at LX. Avoid higher than necessary reverse-

voltage Schottky rectifiers that have higher forward-

voltage drops.

Compensation Network

The device uses an internal transconductance error

amplifier with its inverting input and its output available

to the user for external frequency compensation. The

output capacitor and compensation network determine

the loop stability. The inductor and the output capaci-

tor are chosen based on performance, size, and cost.

Additionally, the compensation network optimizes the

control-loop stability.

The controller uses a current-mode control scheme that

regulates the output voltage by forcing the required current

through the external inductor. The device uses the volt-

age drop across the high-side MOSFET to sense inductor

current. Current-mode control eliminates the double pole

in the feedback loop caused by the inductor and output

capacitor, resulting in a smaller phase shift and requiring

less elaborate error-amplifier compensation than voltage-

mode control. Only a simple single-series resistor (RC)

and capacitor (CC) are required to have a stable, high-

bandwidth loop in applications where ceramic capacitors

are used for output filtering (Figure 3). For other types of

capacitors, due to the higher capacitance and ESR, the

frequency of the zero created by the capacitance and

ESR is lower than the desired closed-loop crossover fre-

quency. To stabilize a nonceramic output capacitor loop,

add another compensation capacitor (CF) from COMP to

GND to cancel this ESR zero.

The basic regulator loop is modeled as a power modula-

tor, output feedback divider, and an error amplifier. The

power modulator has a DC gain set by gmc x RLOAD,

with a pole and zero pair set by RLOAD, the output

capacitor (COUT), and its ESR. The following equations

allow to approximate the value for the gain of the power

modulator (GAINMOD(DC)), neglecting the effect of the

ramp stabilization. Ramp stabilization is necessary when

the duty cycle is above 50% and is internally done for

the device.

LOAD SW

MOD(DC) mc LOAD SW

R f L

GAIN g R (f L)

× ×

= × + ×

where RLOAD = VOUT/ILOUT(MAX) in I, fSW is the switch-

ing frequency in MHz, L is the output inductance in H,

and gmc = 3S.

In a current-mode step-down converter, the output

capacitor, its ESR, and the load resistance introduce a

pole at the following frequency:

pMOD LOAD SW

OUT LOAD SW

1

fR f L

2 C ESR

R (f L)

= 

× ×

π × × +

 

+ ×

 

The output capacitor and its ESR also introduce a zero at:

zMOD OUT

1

f2 ESR C

=π × ×

When COUT is composed of “n” identical capacitors

in parallel, the resulting COUT = n x COUT(EACH) and

ESR = ESR(EACH)/n. Note that the capacitor zero for a

parallel combination of alike capacitors is the same as

for an individual capacitor.

Figure 3. Compensation Network

R2

R1

VREF

VOUT

RC

CC

CF

COMP

gm

�� Maxim Integrated Products 15

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

The feedback voltage-divider has a gain of GAINFB =

VFB/VOUT, where VFB is 1V (typ).

The transconductance error amplifier has a DC gain of

GAINEA(DC) = gm,EA x ROUT,EA, where gm,EA is the error-

amplifier transconductance, which is 900FS (typ), and

ROUT,EA is the output resistance of the error amplifier.

A dominant pole (fdpEA) is set by the compensa-

tion capacitor (CC) and the amplifier output resistance

(ROUT,EA). A zero (fzEA) is set by the compensation

resistor (RC) and the compensation capacitor (CC).

There is an optional pole (fpEA) set by CF and RC to

cancel the output capacitor ESR zero if it occurs near

the crossover frequency (fC, where the loop gain equals

1 (0dB)). Thus:

dpEA C OUT,EA C

1

f2 C (R R )

=π × × +

zEA C C

1

f2 C R

=π × ×

pEA F C

1

f2 C R

=π × ×

The loop-gain crossover frequency (fC) should be set

below 1/5th of the switching frequency and much higher

than the power-modulator pole (fpMOD):

SW

pMOD C

f

f f 5

<< ≤

The total loop gain as the product of the modulator gain,

the feedback voltage-divider gain, and the error-amplifier

gain at fC should be equal to 1. So:

FB

MOD(fC) EA(fC)

OUT

V

GAIN GAIN 1

V

× × =

For the case where fzMOD is greater than fC:

GAINEA(fC) = gm,EA × RC

pMOD

MOD(fC) MOD(dc) C

f

GAIN GAIN f

= ×

Therefore:

FB

MOD(fC) m,EA C

OUT

V

GAIN g R 1

V

× × × =

Solving for RC:

OUT

Cm,EA FB MOD(fC)

V

Rg V GAIN

=× ×

Set the error-amplifier compensation zero formed by RC

and CC (fzEA) at the fpMOD. Calculate the value of CC a

follows:

CpMOD C

1

C2 f R

=π × ×

If fzMOD is less than 5 x fC, add a second capacitor,

CF, from COMP to GND and set the compensation pole

formed by RC and CF (fpEA) at the fzMOD. Calculate the

value of CF as follows:

FzMOD C

1

C2 f R

=π × ×

As the load current decreases, the modulator pole

also decreases; however, the modulator gain increases

accordingly and the crossover frequency remains the

same.

For the case where fzMOD is less than fC:

The power-modulator gain at fC is:

pMOD

MOD(fC) MOD(dc) zMOD

f

GAIN GAIN f

= ×

The error-amplifier gain at fC is:

zMOD

EA(fC) m,EA C C

f

GAIN g R f

= × ×

Therefore:

zMOD

FB

MOD(fC) m,EA C

OUT C

f

V

GAIN g R 1

V f

× × × × =

Solving for RC:

OUT C

Cm,EA FB MOD(fC) zMOD

V f

Rg V GAIN f

×

=× × ×

Set the error-amplifier compensation zero formed by RC

and CC at the fpMOD (fzEA = fpMOD) as follows:

CpMOD C

1

C2 f R

=π × ×

If fzMOD is less than 5 x fC, add a second capacitor CF

from COMP to GND. Set fpEA = fzMOD and calculate CF

as follows:

FzMOD C

1

C2 f R

=π × ×

�� Maxim Integrated Products 16

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

PCB Layout Guidelines

Careful PCB layout is critical to achieve low switching

losses and clean, stable operation. Use a multilayer

board whenever possible for better noise immunity and

power dissipation. Follow these guidelines for good PCB

layout:

1) Use a large contiguous copper plane under the IC

package. Ensure that all heat-dissipating components

have adequate cooling. The bottom pad of the device

must be soldered down to this copper plane for effec-

tive heat dissipation and for getting the full power out

of the IC. Use multiple vias or a single large via in this

plane for heat dissipation.

2) Isolate the power components and high-current path

from the sensitive analog circuitry. This is essential to

prevent any noise coupling into the analog signals.

3) Keep the high-current paths short, especially at the

ground terminals. This practice is essential for stable,

jitter-free operation. The high-current path composed

of input capacitor, high-side FET, inductor, and output

capacitor should be as short as possible.

4) Keep the power traces and load connections short.

This practice is essential for high efficiency. Use

thick copper PCBs (2oz vs. 1oz) to enhance full-load

efficiency.

5) The analog signal lines should be routed away from

the high-frequency planes. This ensures integrity of

sensitive signals feeding back into the IC.

6) The ground connection for the analog and power

section should be close to the IC. This keeps the

ground current loops to a minimum. In cases where

only one ground is used, enough isolation between

analog return signals and high-power signals must

be maintained.

Figure 4. 1.8V/3A Configuration

D1 COUT

100µF

C2

4.7µF

C5

0.1µF

RCOMP

9.1kI

RPGOOD

10kI

RFOSC

62kI

L1

15µH VOUT

1.8V AT 3A

CBST

0.1µF

LX

BST

VOUT

OUT

VBAT

FB

VBIAS

PGOOD

FOSC

CBIAS

1µF

CCOMP2

12pF

BIAS

CCOMP1

821pF

COMP

FSYNC

EN

SUPSWSUP

GND

C1

47µF

C4

0.1µF

C3

4.7µF

POWER GOOD

MAX16909 R1

80.6kI

R2

100kI

�� Maxim Integrated Products 17

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Ordering Information

/V denotes an automotive qualified part.

+Denotes a lead(Pb)-free/RoHS-compliant package.

*Future product—contact factory for availability.

**EP = Exposed pad.

Package Information

For the latest package outline information and land patterns

(footprints), go to www.maxim-ic.com/packages. Note that a

“+”, “#”, or “-” in the package code indicates RoHS status only.

Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.

Chip Information

PROCESS: BiCMOS

PART TEMP RANGE PIN-PACKAGE

MAX16909RAUE/V+ -40NC to +125NC16 TSSOP-EP**

MAX16909RATE/V+* -40NC to +125NC16 TQFN-EP**

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

16 TSSOP-EP U16E+3 21-0108 90-0120

16 TQFN-EP T1655+4 21-0140 90-0121

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.

Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 18

MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 3/11 Initial release —