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High-Voltage, 2.2MHz, 2A Automotive Step-

Down Converter with Low Operating Current

MAX16974

General Description

The MAX16974 is a 2A, current-mode, step-down con-

verter with an integrated high-side switch. It is designed

to operate with 3.5V to 28V input voltages, while using

only 35FA quiescent current at no load. The switching

frequency is adjustable from 220kHz to 2.2MHz by an

external resistor and can be synchronized to an external

clock. The output voltage is pin selectable to be 5V fixed

or 1V to 10V adjustable. The wide input voltage range

makes the device ideal for automotive and industrial

applications.

The device operates in skip mode for reduced current

consumption in light-load applications. An adjustable

reset threshold helps keep microcontrollers alive down to

their lowest specified input voltage. Protection features

include cycle-by-cycle current limit, overvoltage, and

thermal shutdown with automatic recovery. The device

also features a power-good monitor to ease power-

supply sequencing.

The device operates over the -40°C to +125°C auto-

motive temperature range and is available in a 16-pin

TSSOP-EP package.

Applications

Automotive

Industrial

Features

S Wide 3.5V to 28V Input Voltage Range

S 42V Input Transient Tolerance

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

S Integrated 2A Internal High-Side Switch

S Adjustable Switching Frequency (220kHz to

2.2MHz)

S Operates Through Cold Crank with High Duty

Cycle

S Frequency Synchronization Input

S Internal Boost Diode

S 35µA Skip-Mode Operating Current

S 5µA Typical Shutdown Current

S Adjustable Power-Good Output Level and Timing

S 3.3V Logic Level to 42V Compatible Enable Input

S Current-Limit, Thermal-Shutdown, and

Overvoltage Protections

S Automotive Temperature Range: -40°C to +125°C

S AEC-Q100 Qualified

19-5630; Rev 1; 7/11

Typical Application Circuit

Ordering Information

/V Denotes an automotive qualified part.

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

*EP = Exposed pad.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX16974AUE/V+

-40NC to +125NC

16 TSSOP-EP*

MAX16974

OUT

22µF

IN2

4.7µF

IN1

47µF

CRES

100pF

COMP

20kI

RES

10kI

FOSC

12.1kI

4.7µH

OUT

5V AT 2A

BST

0.1µF

BST

OUT

PLACE C

IN2

(4.7µF) AND C

IN3

(0.1µF) NEXT TO SUP.

PLACE C

IN4

(0.1µF) AND C

IN5

(4.7µF) NEXT TO SUPSW.

OUT

BIAS

BAT

RESETI

BIAS

RES

FOSC

CRES

BIAS

1µF

COMP2

OPEN

BIAS

COMP1

5600pF

COMP

FSYNC

SUPSWSUP

IN3

0.1µF

IN4

0.1µF

IN5

4.7µF

GND

Summary of content (19 pages)

PAGE 1
9-5630; Rev 1; 7/11 TION KIT EVALUA BLE AVAILA High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current Features The MAX16974 is a 2A, current-mode, step-down converter with an integrated high-side switch. It is designed to operate with 3.5V to 28V input voltages, while using only 35FA quiescent current at no load. The switching frequency is adjustable from 220kHz to 2.2MHz by an external resistor and can be synchronized to an external clock.
PAGE 2
MAX16974 High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current ABSOLUTE MAXIMUM RATINGS SUP, SUPSW, EN to GND......................................-0.3V to +45V SUP to SUPSW, LX................................................-0.3V to +0.3V BST to GND . .........................................................-0.3V to +47V BST to LX ................................................................-0.3V to +6V OUT to GND...........................................................-0.
PAGE 3
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current (VSUP = VSUPSW = 14V, L1 = 4.7FH, VEN = 14V, CIN = 10FF, COUT = 22FF, CBIAS = 1FF, CBST = 0.1FF, CCRES = 1nF, RFOSC = 12.1kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (VSUP = VSUPSW = 14V, L1 = 4.7FH, VEN = 14V, CIN = 10FF, COUT = 22FF, CBIAS = 1FF, CBST = 0.1FF, CCRES = 1nF, RFOSC = 12.1kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) PARAMETER SYMBOL CRES Source Current ICRES CRES Pulldown Current CONDITIONS VOUT in regulation ICRES_PD MIN TYP MAX 9.5 10 10.5 UNITS FA VOUT out of regulation 1 mA RES Sink Current VRES pulls low, VRES > 0.
PAGE 5
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current LOAD TRANSIENT UNDERVOLTAGE PULSE MAX16974 toc06 MAX16974 toc07 200mV/div VOUT 5V/div VSUP 0V 0V SF = 400kHz VOUT ACCOUPLED ILOAD 5V/div VOUT 0V 1A/div 0A 5V/div 0V SF = 2.2MHz VRES 20ms/div SWITCHING FREQUENCY vs. TEMPERATURE RESET TIMEOUT PERIOD vs.
PAGE 6
Typical Operating Characteristics (continued) (VSUP = VSUPSW = 14V, VOUT = 5V, FSYNC = GND, fOSC = 400kHz, TA = +25NC, unless otherwise noted. See Figure 1.) 2.4 2.0 1.6 1.2 0.8 420 ILOAD = 1A 418 SWITCHING FREQUENCY (kHz) MAX16974 toc12 0.4 416 414 412 410 408 406 404 402 400 0 6 12 22 32 42 52 62 72 82 92 102 112 122 8 10 12 14 16 18 20 22 24 26 28 SUPPLY VOLTAGE (V) RFOSC (kI) FSYNC TRANSITION FROM INTERNAL TO EXTERNAL FREQUENCY (5V/2.2MHz CONFIGURATION) VOUT vs.
PAGE 7
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current OUTPUT RESPONSE TO SLOW INPUT RAMP UP (5V/400kHz) OUTPUT RESPONSE TO SLOW INPUT RAMP DOWN (5V/2.2MHz) MAX16974 toc18 ILOAD = 2A MAX16974 toc19 10V/div VSUP VSUP 0 VOUT 5V/div 0 VLX 10V/div 2V/div 0 VOUT 0 2V/div 0 VLX 2V/div 5V/div 0 VRES 0 10s/div 10s/div DIPS AND DROP TEST (5V/2.
PAGE 8
VBAT CIN1 47µF CIN2 4.7µF CIN3 0.1µF SUP EN SUPSW CBST 0.1µF CCOMP1 5600pF RCOMP 20kI L1 VOUT = 15µH 3.3V AT 2A AT 300kHz VOUT MAX16974 RESETI COUT1 47µF VBIAS RFB2 56kI BIAS CRES COUT 47µF RFB1 124kI FB FOSC CCRES 1nF D1 OUT RFOSC 82kI CBIAS 1µF CIN5 4.7µF LX COMP CCOMP2 OPEN CIN4 0.1µF BST FSYNC RRES 10kI RES GND PLACE CIN2 (4.7µF) AND CIN3 (0.1µF) NEXT TO SUP. PLACE CIN4 (0.1µF) AND CIN5 (4.7µF) NEXT TO SUPSW. Figure 1. 3.
PAGE 9
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current PIN NAME FUNCTION 1 CRES Analog Reset Timer. CRES sources 10FA (typ) of current into an external capacitor to set the reset timeout period. Reset timeout period is defined as the time between the start of output regulation and RES going high impedance. Leave unconnected for minimum delay time. 2 FOSC Resistor-Programmable Switching-Frequency Setting Control Input.
PAGE 10
MAX16974 High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current Detailed Description The MAX16974 is a constant-frequency, current-mode, automotive buck converter with an integrated high-side switch. The device operates with 3.5V to 28V input voltages and tolerates input transients up to 42V. During undervoltage events, such as cold-crank conditions, the internal pass device maintains up to 92% duty cycle. An open-drain, active-low reset output helps monitor the output voltage.
PAGE 11
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current External Clock Input (FSYNC) The device synchronizes to an external clock signal applied at FSYNC. The signal at FSYNC must have a 10% shorter period than the internal clock period for proper synchronization. The internal clock signal takes over if the externally applied signal has a frequency lower than the internal clock frequency.
PAGE 12
MAX16974 High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current Skip Mode During light-load operation, IINDUCTOR P 240mA, the device enters skip-mode operation. Skip mode turns off the internal switch 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 converter skips unnecessary cycles, the converter efficiency increases.
PAGE 13
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current MAX16974 toc12 2.8 SWITCHING FREQUENCY (MHz) IBST(DROPOUT) = 3mA (worst case) 2.4 dt (no load) = 16 clock cycles dV (BST capacitor) = VOUT - 2.7V. Reset Timeout Period 2.0 The device offers a capacitor-adjustable reset timeout period. Connect up to 0.1FF capacitor from CRES to GND to set the timeout period. CRES can source 10FA of current. Use the following formula to set the timeout period: 1.6 1.2 0.8 0.
PAGE 14
MAX16974 High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current 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 Table 1 shows a comparison between small and large inductor sizes. The inductor value must be chosen so the maximum inductor current does not reach the minimum current limit of the device.
PAGE 15
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current Soft-Start Time and Maximum Allowed Output Capacitance The device’s soft-start time depends on the selected switching frequency. The soft-start time is fixed to 2048 cycles, regardless of the switching frequency. This means at 2.2MHz the soft-start time is ~0.93ms, and at 220kHz the soft-start time is ~9.3ms.
PAGE 16
MAX16974 High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current the voltage drop across the high-side MOSFET. Currentmode 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.
PAGE 17
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current GAINMOD(fC) × VFB × GAINEA(fC) = 1 VOUT For the case where fzMOD is greater than fC: GAINEA(fC) = g m,EA × R C GAINMOD(fC) = GAINMOD(DC) × fpMOD fC V GAINMOD(fC) × FB × g m,EA × R C = 1 VOUT Solving for RC: VOUT g m,EA × VFB × GAINMOD(fC) Set the error-amplifier compensation zero formed by RC and CC (fzEA) at the fpMOD.
PAGE 18
MAX16974 High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current 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.
PAGE 19
High-Voltage, 2.2MHz, 2A Automotive StepDown Converter with Low Operating Current REVISION NUMBER REVISION DATE 0 11/10 Initial release — 1 7/11 Corrected the GAINMOD(DC) and fpMOD equations in the Compensation Network section 16 DESCRIPTION PAGES CHANGED Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.