Rainbow Electronics MAX1637 User Manual

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General Description

The MAX1637 synchronous, buck, switch-mode power­supply controller generates the CPU supply voltage in
battery-powered systems. The MAX1637 is a stripped­down version of the MAX1636 in a smaller 16-pin QSOP
package. The MAX1637 is intended to be powered sep­arately from the battery by an external bias supply (typi­cally the +5V system supply) in applications where the
battery exceeds 5.5V. The MAX1637 achieves excellent
DC and AC output voltage accuracy. This device can
operate from a low input voltage (3.15V) and delivers the
excellent load-transient response needed by upcoming
generations of dynamic-clock CPUs.

Using synchronous rectification, the MAX1637 achieves
up to 95% efficiency. Efficiency is greater than 80%
over a 1000:1 load-current range, which extends bat­tery life in system-suspend or standby mode. Excellent
dynamic response corrects output load transients
caused by the latest dynamic-clock CPUs within five
300kHz clock cycles. Powerful 1A on-board gate driv­ersensure fast external N-channel MOSFET switching.

The MAX1637 features a logic-controlled and synchro­nizable, fixed-frequency, pulse-width-modulation
(PWM) operating mode. This reduces noise and RF
interference in sensitive mobile-communications and
pen-entry applications. Asserting the SKIP pin enables
fixed-frequency mode, for lowest noise under all load
conditions. For a stand-alone device that includes a
+5V VL linear regulator and low-dropout capabilities,
refer to the MAX1636 data sheet.

________________________Applications

Notebook Computers Subnotebook Computers
Handy-Terminals, PDAs

____________________________Features

♦ ±2% DC Accuracy
♦ 0.1% (typ) DC Load Regulation
♦ Adjustable Switching Frequency to 350kHz
♦ Idle Mode™ Pulse-Skipping Operation
♦ 1.10V to 5.5V Adjustable Output Voltage
♦ 3.15V Minimum IC Supply Voltage (at V

CC

pin)

♦ Internal Digital Soft-Start
♦ 1.1V ±2% Reference Output
♦ 1µA Total Shutdown Current
♦ Output Overvoltage Crowbar Protection
♦ Output Undervoltage Shutdown (foldback)
♦ Tiny 16-Pin QSOP Package

MAX1637

Miniature, Low-Voltage,

Precision Step-Down Controller

________________________________________________________________

Maxim Integrated Products

1

16
15
14
13
12
11
10

9

1
2
3
4
5
6
7
8

CSH SKIP

LX
DH
BST
PGND
DL
V

GG

V

CC

TOP VIEW

MAX1637

QSOP

CSL

FB

SHDN

CC

REF

SYNC

GND

__________________Pin Configuration

__________Typical Operating Circuit

19-1321; Rev 1; 2/98

PART

MAX1637EEE -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 QSOP

EVALUATION KIT

AVAILABLE

______________Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

MAX1637

SHDN

GND

V

BATT

V

BIAS

DL

PGND

LX

DH

V

CC

V

GG

BST

CSH
CSL

FB

SKIP

SYNC

REF

CC

OUTPUT

MAX1637

Miniature, Low-Voltage,
Precision Step-Down Controller

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VCC= VGG= 5V, SYNC = VCC, I

REF

= 0mA, TA= 0°C to +85°C, unless otherwise noted. Typical values are at

T

A

= +25°C.)

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

GND to PGND .............................................................+2V to -2V

LX, BST to GND......................................................-0.3V to +36V

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

V

CC

, VGG, CSL, CSH, SHDN to GND.......................-0.3V to +6V

DL to GND..................................................-0.3V to (V

GG

+ 0.3V)

REF, SKIP, SYNC, CC to GND ...................-0.3V to (V

CC

+ 0.3V)

REF Output Current.............................................................20mA

REF Short-Circuit to GND..............................................Indefinite

Operating Temperature Range ...........................-40°C to +85°C

Continuous Power Dissipation (T

A

= +70°C)

QSOP (derate 8.3mW/°C above +70°C)......................667mW

Storage Temperature Range.............................-65°C to +160°C

Junction Temperature......................................................+150°C

Lead Temperature (soldering, 10sec).............................+300°C

SYNC = GND

SYNC = V

CC

FB tied to V

OUT

, 0mV < (CSH - CSL) < 80mV,

includes line and load regulation

VCC= 3.15V to 5.5V

REF load = 0µA to 50µA

VCC, V

GG

REF load = 0µA

Rising edge, hysteresis = 15mV

Rising edge, hysteresis = 15mV

SHDN = GND, VCC= V

GG

CSH - CSL = 0mV to CSH - CSL = 100mV

CSH - CSL

VCC= 5V
VCC= 3.3V

SHDN to full current limit, four levels

VFB= V

REF

CONDITIONS

170 200 230

Oscillator Frequency kHz

270 300 330

mV3REF Line Regulation

mV10REF Load Regulation

V1.080 1.100 1.120REF Output Voltage

V2.80 3.05VGGUndervoltage Lockout Threshold

V2.80 3.05VCCUndervoltage Lockout Threshold

%2AC Load Regulation

mV20 30 40Idle-Mode Switchover Threshold

clocks512Soft-Start Ramp Time

nA-50 50FB Input Current

V3.15 5.5Input Voltage Range

µA0.5 3Shutdown Supply Current

V1.080 1.100 1.120Output Voltage

V

REF

5.5

Output Adjustment Range V

V

REF

3.6

UNITSMIN TYP MAXPARAMETER

CSH > CSL
CSH < CSL

80 100 120

Current-Limit Threshold mV

-145 -100 -55

Output not switching

1.5 2.5

Power Consumption mW

1 1.75

SYNC = GND

SYNC = V

CC

ns200SYNC Input Pulse Width High

%

93 96

89 92

Maximum Duty Factor

(Note 1)

kHz240 340SYNC Input Frequency Range

ns200SYNC Input Rise/Fall Time

ns200SYNC Input Pulse Width Low

VCC= VGG= 5V
VCC= VGG= 3.3V

SMPS CONTROLLER

INTERNAL REFERENCE

OSCILLATOR

MAX1637

Miniature, Low-Voltage,

Precision Step-Down Controller

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VCC= VGG= 5V, SYNC = VCC, I

REF

= 0mA, TA= 0°C to +85°C, unless otherwise noted. Typical values are at

T

A

= +25°C.)

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VCC= VGG= 5V, SYNC = VCC, I

REF

= 0mA, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

High or low, DH or DL

DH or DL forced to 2V

CSH = CSL = 5V, VCC= VGG= GND,
either CSH or CSL input

FB to DL delay, 22mV overdrive, C

GATE

= 2000pF

FB, with respect to regulation point

From shutdown or power-on-reset state

Pin at GND or V

CC

SHDN, SKIP, SYNC

% of nominal output

SHDN, SKIP, SYNC

CONDITIONS

Ω7Gate Driver On-Resistance

A1Gate Driver Sink/Source Current

µA10Current-Sense Input Leakage Current

µA-1 1Logic Input Bias Current

V0.8Logic Input Voltage Low

V2.4Logic Input Voltage High

µs1.25Overvoltage Fault Propagation Delay

%4 7 10Overvoltage Trip Threshold

clocks6144Output Undervoltage Lockout Delay

%60 70 80Output Undervoltage Lockout Threshold

UNITSMIN TYP MAXPARAMETER

FB tied to V

OUT

, 0mV < (CSH - CSL) < 80mV,

includes line and load regulation

SYNC = GND

VCC, V

GG

SYNC = V

CC

Rising edge, hysteresis = 15mV

Rising edge, hysteresis = 15mV

VCC= 3.3V

VCC= VGG= 3.3V, output not switching

VCC= 5V

VCC= VGG= 5V, output not switching

CSH > CSL

CONDITIONS

kHz240 340SYNC Input Frequency Range

ns200SYNC Input Rise/Fall Time

ns200SYNC Input Pulse Width Low

ns200SYNC Input Pulse Width High

kHz

170 230

Oscillator Frequency

262 338

V2.80 3.05VGGUndervoltage Lockout Threshold

V2.80 3.05VCCUndervoltage Lockout Threshold

mW1.75

Power Consumption

mW2.5

mV70 130Current-Limit Threshold

V1.080 1.120Output Voltage

V3.15 5.5Input Voltage Range

V

REF

3.6

Output Adjustment Range V

V

REF

5.5

UNITSMIN TYP MAXPARAMETER

OVERVOLTAGE PROTECTION

INPUTS AND OUTPUTS

SMPS CONTROLLER

INTERNAL REFERENCE

OSCILLATOR

0

10

5

15

20

0 3 41 2 5 6 87 9

SUPPLY CURRENT

vs. LOAD CURRENT

MAX1637-07

LOAD CURRENT (A)

V

CC

+ V

GG

SUPPLY CURRENT (mA)

SYNC = HIGH

SYNC = LOW

SKIP = LOW

MAX1637

Miniature, Low-Voltage,
Precision Step-Down Controller

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VCC= VGG= 5V, SYNC = VCC, I

REF

= 0mA, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

SHDN, SKIP, SYNC

SHDN, SKIP, SYNC

% of nominal output

FB, with respect to regulation point

CONDITIONS

V0.8Logic Input Voltage Low

V2.4Logic Input Voltage High

%60 80Output Undervoltage Lockout Threshold

%4.0 10Overvoltage Trip Threshold

UNITSMIN TYP MAXPARAMETER

Note 1: Guaranteed by design, not production tested.
Note 2: Specifications from -40°C to 0°C are guaranteed by design and not production tested.

__________________________________________Typical Operating Characteristics

(V

OUT

= 3.3V, TA = +25°C, unless otherwise noted.)

100

50

0.01 1010.1

EFFICIENCY vs. LOAD CURRENT

(1.7V/7A CIRCUIT)

70

60

90

80

MAX1637-01

LOAD CURRENT (A)

EFFICIENCY (%)

SKIP = LOW

V

BATT

= 7V

V

BATT

= 15V

V

BATT

= 22V

100

0

0.001 1010.01 0.1

EFFICIENCY vs. LOAD CURRENT

(2.5V/3A CIRCUIT)

40
30
20
10

80
70

90

60
50

MAX1637-02

LOAD CURRENT (A)

EFFICIENCY (%)

V

BATT

= 15V

SKIP = LOW

V

BATT

= 7V

V

BATT

= 22V

100

50

0.01 1010.1

EFFICIENCY vs. LOAD CURRENT

(2.5V/2A CIRCUIT)

70

60

90

80

MAX1637-03

LOAD CURRENT (A)

EFFICIENCY (%)

V

BATT

= 7V

SKIP = LOW

V

BATT

= 15V

V

BATT

= 22V

100

50

0.01 1010.1

EFFICIENCY vs. LOAD CURRENT

(3.3V/3A CIRCUIT)

70

60

90

80

MAX1637-04

LOAD CURRENT (A)

EFFICIENCY (%)

V

BATT

= 5V

V

BATT

= 30V

V

BATT

= 15V

SKIP = LOW

0

10

5

15

20

3.0 4.03.5 4.5 5.0

5.5

6.0

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX1637-06

SUPPLY VOLTAGE (V)

V

CC

+ V

GG

SUPPLY CURRENT (mA)

I

LOAD

= 1A

V

OUT

= 3.3V

SKIP = HIGH

SKIP = LOW

OVERVOLTAGE PROTECTION

INPUTS AND OUTPUTS

MAX1637

Miniature, Low-Voltage,

Precision Step-Down Controller

_______________________________________________________________________________________

5

10

-10

0.01 1010.1

LOAD REGULATION

vs. LOAD CURRENT

-2

-6

-8

6

8

4

0

-4

2

MAX1637-08

LOAD CURRENT (A)

LOAD REGULATION ∆V

OUT

(mV)

0

0.3

0.2

0.1

0.4

0.5

0.6

0 403010 20 50 60 70 80 90 100

REF LOAD-REGULATION ERROR

vs. REF LOAD CURRENT

MAX1637-09

REF LOAD CURRENT (µA)

REF LOAD REGULATION ∆V (mV)

900

0

0.01 1010.1

DROPOUT VOLTAGE

vs. LOAD CURRENT

300
200

100

700

800

600

400

500

MAX1637-10

LOAD CURRENT (A)

DROPOUT VOLTAGE (mV)

V

OUT

FORCED TO 3.27V

SYNC = V

CC

V

OUT

20mV/div

V

LX

INDUCTOR
CURRENT

1A

0V

5V

0A

SWITCHING WAVEFORMS

(PWM MODE)

MAX1637-13

1µs/div

V

OUT

50mV/div

LOAD
CURRENT

0A

2A

4A

LOAD-TRANSIENT RESPONSE

(3.3V/3A, PWM MODE)

MAX1637 TOC11

100µs/div

V

OUT

50mV/div

5A LOAD CURRENT
0A

10A

LOAD-TRANSIENT RESPONSE

(1.8V, PWM MODE)

MAX1637 TOC12

100µs/div

V

OUT

50mV/div

V

LX

INDUCTOR
CURRENT

1A

0V

5V

0A

SWITCHING WAVEFORMS

(PFM MODE)

MAX1637-14

20µs/div

V

OUT

= 1.7V

1µs/div

SWITCHING WAVEFORMS

DROPOUT OPERATION

MAX1637-15

V

OUT

10mV/div

V

LX

2V/div

INDUCTOR
CURRENT

1A
0A

V

OUT

FORCED TO 3.27V

SYNC = V

CC

____________________________________Typical Operating Characteristics (continued)

(V

OUT

= 3.3V, TA = +25°C, unless otherwise noted.)

MAX1637

Miniature, Low-Voltage,
Precision Step-Down Controller

6 _______________________________________________________________________________________

____________________________________Typical Operating Characteristics (continued)

(V

OUT

= 3.3V, TA = +25°C, unless otherwise noted.)

500µs/div

TIME EXITING SHUTDOWN
(V

OUT

= 3.3V, I

LOAD

= 7A)

MAX1637-16

V

OUT

1V/div

V

SHDN

5V/div

V

OUT

100mV/div

V

DL

INDUCTOR
CURRENT

-5A

0A

0V

5V

-10A

OVERVOLTAGE-PROTECTION WAVEFORMS

(V

IN

SHORTED TO V

OUT

THROUGH A 0.5Ω RESISTOR)

MAX1637-17

10µs/div

______________________________________________________________Pin Description

PIN

High-Side Current-Sense InputCSH1

FUNCTIONNAME

Low-Side Current-Sense InputCSL2

Compensation Pin. Connect a small capacitor to GND to set the integration time constant.CC4

Feedback Input. Connect to center of resistor divider.FB3

Shutdown Control Input. Turns off entire IC. When low, reduces supply current below 0.5µA (typ). Drive with
logic input or connect to RC network between GND and VCCfor automatic start-up.

SHDN

6

Analog GroundGND8

Oscillator Frequency Select and Synchronization Input. Tie to VCCfor 300kHz operation; tie to GND for
200kHz operation.

SYNC7

1.100V Reference Output. Capable of sourcing 50µA for external loads. Bypass with 0.22µF minimum.REF5

Gate-Drive and Boost-Circuit Power Supply. Can be driven from a supply other than VCC. If the same supply
is used by both VCCand VGG, isolate VCCfrom VGGwith a 20Ω resistor. Bypass to PGND with a 4.7µF
capacitor. VGGcurrent = (QG1+ QG2) x f, where QGis the MOSFET gate charge at VGS= VGG.

V

GG

10

Power GroundPGND12

Low-Side Gate-Driver OutputDL11

High-Side Gate-Driver OutputDH14

Low-Noise Mode Control. Forces fixed-frequency PWM operation when high.

SKIP

16

Inductor ConnectionLX15

Boost Capacitor ConnectionBST13

Main Analog Supply-Voltage Input to the Chip. VCCpowers the PWM controller, logic, and reference. Input
range is 3.15V to 5.5V. Bypass to GND with a 0.1µF capacitor close to the pin.

V

CC

9