Rainbow Electronics MAX1639 User Manual

________________General Description

The MAX1639 is an ultra-high-performance, step-down
DC-DC controller for CPU power in high-end computer
systems. Designed for demanding applications in which
output voltage precision and good transient response are
critical for proper operation, it delivers over 35A from 1.1V
to 4.5V with ±1% total accuracy from a +5V ±10% supply.
Excellent dynamic response corrects output transients
caused by the latest dynamically clocked CPUs. This
controller achieves over 90% efficiency by using synchro­nous rectification. Flying-capacitor bootstrap circuitry
drives inexpensive, external N-channel MOSFETs.

The switching frequency is pin-selectable for 300kHz,
600kHz, or 1MHz. High switching frequencies allow the
use of a small surface-mount inductor and decrease out­put filter capacitor requirements, reducing board area
and system cost.

Output overvoltage protection is enforced by a crowbar
circuit that turns on the low-side MOSFET with 100%
duty factor when the output is 200mV above the normal
regulation point. Other features include internal digital
soft-start, a power-good output, and a 3.5V ±1% refer­ence output. The MAX1639 is available in a 16-pin
narrow SOIC package.

________________________Applications

Local DC-DC Converters for CPUs
Workstations
Desktop Computers
LAN Servers
GTL Bus Termination

____________________________Features

♦ Better than ±1% Output Accuracy Over

Line and Load

♦ Greater than 90% Efficiency Using N-Channel

MOSFETs

♦ Pin-Selected High Switching Frequency:

300kHz, 600kHz, or 1MHz

♦ Over 35A Output Current
♦ Resistor-Divider Adjustable Output from

1.1V to 4.5V

♦ Current-Mode Control for Fast Transient

Response and Cycle-by-Cycle Current-Limit
Protection

♦ Short-Circuit Protection with Foldback Current

Limiting

♦ Crowbar Overvoltage Protection
♦ Power-Good (PWROK) Output
♦ Digital Soft-Start
♦ High-Current (2A) Drive Outputs

MAX1639

High-Speed Step-Down Controller with

Synchronous Rectification for CPU Power

________________________________________________________________

Maxim Integrated Products

1

19-1337; Rev 0; 2/98

PART

MAX1639ESE -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 Narrow SO

_______________Ordering Information

__________

Typical Operating Circuit

Pin Configuration appears at end of data sheet.

V

CC

AGND

REF

FREQ
CC1
CC2

DL

PWROK

LX

BST

DH

PGND

TO V

DD

CSH

OUTPUT

1.1V TO 4.5V

INPUT

+5V

V

DD

CSL

FB

MAX1639

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone] ext. 3468.

EVALUATION KIT

AVAILABLE

FREQ Input Voltage

MAX1639

High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= VCC= +5V, PGND = AGND = 0V, FREQ = REF, TA= 0°C to +85°C, unless otherwise noted.)

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.

VDD, VCC, PWROK to AGND....................................-0.3V to +6V

PGND to AGND ..................................................................±0.3V

CSH, CSL to AGND....................................-0.3V to (VCC+ 0.3V)

DL to PGND................................................-0.3V to (VDD+ 0.3V)

REF, CC1, CC2, FREQ, FB to AGND .........-0.3V to (V

CC

+ 0.3V)

BST to PGND..........................................................-0.3V to +12V

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

DH to LX.............................................(LX - 0.3V) to (BST + 0.3V)

Continuous Power Dissipation (TA= +70°C)

16-Pin Narrow SO (derate 8.70mW/°C above +70°C) ....696mW

SO θJC...........................................................................65°C/W

Operating Temperature Range

MAX1639ESE....................................................-40°C to +85°C

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

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

FREQ = AGND

FREQ = REF

VCC= V

DD

FREQ = V

CC

PWROK = 5.5V

Includes line and load
regulation errors

I

SINK

= 2mA, VCC= 4.5V

Falling FB, 1% hysteresis with respect to V

REF

Rising FB, 1% hysteresis with respect to V

REF

0µA < I

REF

< 100µA

No load

VCC= VDD= 5.5V, FB forced 60mV above
regulation point, operating or standby mode

VCCrising edge, 1% hysteresis

V

REF

= 0V

Rising edge, 1% hysteresis

CONDITIONS

kHz

255 300 345

Switching Frequency 540 600 660

850 1000 1150

µA1PWROK Output Current High

V0.4PWROK Output Voltage Low

%

6.5 8 9.5

PWROK Trip Level

-7.5 -6 -4.5

mA0.5 4.0Reference Short-Circuit Current

V2.7 3.0Reference Undervoltage Lockout

V4.5 5.5Input Voltage Range

V

1.083 1.117

1.089 1.111

FB Voltage

mV10Reference Load Regulation

V3.465 3.5 3.535Reference Voltage

mA0.1VDDSupply Current (IDD)

V4.0 4.2Input Undervoltage Lockout

UNITSMIN TYP MAXPARAMETER

TA= +25°C to +85°C
TA= 0°C to +85°C

2.5

5

CSH - CSL = 0mV to 80mV %1AC Load Regulation
CSH - CSL = 0mV to 80mV %0.1DC Load Regulation

FB overdrive = 60mV
FB overdrive = 0V

Operating
mode

mA

3.6 10

VCC= V

DD

= 5.5V

V

REF

= 0V

Shutdown
mode

VCCSupply Current (ICC)

VCC(high)

GND (low)

FREQ = V

CC

%

VCC- 0.1

Maximum Duty Cycle

0.2

85 90

FREQ Input Voltage V

REF (mid) 3.3 3.7

ELECTRICAL CHARACTERISTICS (continued)

(VDD= V

CC

= +5V, PGND = AGND = 0V, FREQ = REF, TA= 0°C to +85°C, unless otherwise noted.)

MAX1639

_______________________________________________________________________________________

3

High-Speed Step-Down Controller with

Synchronous Rectification for CPU Power

15 38 70

mV

FB = 0V (foldback)

Current-Limit Trip Voltage

DL On-Resistance Ω

50 µABST = 12V, LX = 7V, REF = GNDBST Leakage Current

1536 1 / f

OSC

To full current limitSoft-Start Time

85 100 115FB = 1.1V

FB Input Current

CC2 Clamp Voltage

PARAMETER MIN TYP MAX UNITS

FREQ Input Current 4 µA

±0.1 µA

2.4 3.0
V

4 V

CC

CC2 Source/Sink Current 100 µA

0.7 2DH On-Resistance

Maximum

0.7 2

Ω

DH, DL Source/Sink Current 2 A
DH, DL Dead Time 0 30 ns

CONDITIONS

Minimum

30mV overdrive
BST - LX = 4.5V
VDD= 4.5V
DH = DL = 2.5V

ELECTRICAL CHARACTERISTICS

(VDD= VCC= +5V, PGND = AGND = 0V, FREQ = REF, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

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

FREQ = REF

FREQ = V

CC

BST - LX = 4.5V

FREQ = V

CC

Falling FB, 1% hysteresis with respect to V

REF

Rising FB, 1% hysteresis with respect to V

REF

FREQ = AGND

VDD= 4.5V

Ω2

%84

DL On-Resistance

VCCrising edge, 1% hysteresis

Ω

VCC= V

DD

2

CONDITIONS

510 690

Maximum Duty Cycle

800 1200

DH On-Resistance

Switching Frequency

FB = 1.1VCurrent-Limit Trip Voltage mV70 130

6 10

kHz

240 360

%

-8 -4

PWROK Trip Level

V3.9 4.3Input Undervoltage Range

V4.5 5.5Input Voltage Range

UNITSMIN TYP MAXPARAMETER

CC2 Transconductance

CC1 Output Resistance 10 kΩ

1 mmho

CSH, CSL Input Current 50 µACSH = CSL = 1.1V

VCC= VDD=

5.5V

mA

12

VDDSupply Current

3

Includes line and load regulation errors

No load

V1.072 1.128FB Voltage

V3.448 3.553Reference Voltage

VCC= VDD= 5.5V, FB forced 60mV above
regulation point, operating or shutdown mode

mA0.2VDDSupply Current

Operating mode FB overdrive = 60mV

VREF = 0VShutdown mode

MAX1639

High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power

4 _______________________________________________________________________________________

FOLDBACK CURRENT LIMIT

(V

OUT

= 2.5V, NOMINAL)

MAX1639-02

A: V

OUT

= 0.5V/div

B: INDUCTOR CURRENT, 5A/div

A

B

10µs/div

START-UP WAVEFORMS

MAX1639-03

A: INDUCTOR CURRENT, 2A/div
B: V

OUT

= 1V/div

A

B

400µs/div

1µs/div

SWITCHING WAVEFORMS

C

0

MAX1639-04

VIN = 5V, V

OUT

= 2.5V, LOAD = 0A

A: V

OUT

, 20mV/div
B: INDUCTOR CURRENT, 2A/div
C: LX, 5V/div

B

A

LOAD-TRANSIENT RESPONSE

(V

OUT

= 2.5V)

MAX1639-01

VIN = 5V, V

OUT

= 2.5V, LOAD = 8A

A: V

OUT

, 100mV/div, AC COUPLED

B: INDUCTOR CURRENT, 5A/div

A

B

10µs/div

__________________________________________Typical Operating Characteristics

(TA = +25°C, using the MAX1639 evaluation kit, unless otherwise noted.)

100

50

0.1 10

EFFICIENCY vs. OUTPUT CURRENT

60

90

80

70

MAX1639-05

OUTPUT CURRENT (A)

EFFICIENCY (%)

1

3.5V

1.8V

2.5V

50

55

0

MAXIMUM DUTY CYCLE vs.

SWITCHING FREQUENCY

65
60

70

MAX1639-06

SWITCHING FREQUENCY (kHz)

MAXIMUM DUTY CYCLE (%)

85

95
90

75

80

200 800 1000 1200

100

600400