Maxim MAX1638EEG, MAX1638EAG Datasheet

_______________General Description

The MAX1638 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 1.3V
to 3.5V 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.

The MAX1638 is available in 24-pin SSOP and QSOP
(future package) packages, and offers additional fea­tures such as a digitally programmable output;
adjustable transient response; and selectable 0.5%, 1%,
or 2% AC load regulation. Fast recovery from load tran­sients is ensured by a GlitchCatcher™ current-boost cir­cuit that eliminates delays caused by the buck inductor.
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.

________________________Applications

Pentium Pro™, Pentium II™, PowerPC™, Alpha™,
and K6™ Systems

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
♦ Digitally Programmable Output from 1.3V to 3.5V
♦ Current-Mode Control for Fast Transient

Response and Cycle-by-Cycle Current-Limit
Protection

♦ Short-Circuit Protection with Foldback Current

Limiting

♦ Glitch-Catcher Circuit for Fast Load-Transient

Response

♦ Crowbar Overvoltage Protection
♦ Power-Good (PWROK) Output
♦ Digital Soft-Start
♦ High-Current (2A) Drive Outputs
♦ Complies with Intel VRM 8.2 Specification

MAX1638

High-Speed Step-Down Controller with

Synchronous Rectification for CPU Power

________________________________________________________________

Maxim Integrated Products

1

19-1313; Rev 0; 11/97

PART

MAX1638EAG
MAX1638EEG* -40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

24 SSOP
24 QSOP

______________Ordering Information

__________Typical Operating Circuit

Pin Configuration appears at end of data sheet.

*

Future product—contact factory for package availability.

Pentium Pro and Pentium II are trademarks of Intel Corp.
PowerPC is a trademark of IBM Corp.
Alpha is a trademark of Digital Equipment Corp.
K6 is a trademark of Advanced Micro Devices.
GlitchCatcher is a trademark of Maxim Integrated Products.

V

CC

AGND

REF
LG

FREQ
CC1
CC2

DL

PWROK
D0

LX

BST

DH

PGND

TO V

DD

CSH

OUTPUT

1.3V TO 4.5V

INPUT

+5V

V

DD

CSL

FB

MAX1638

D1
D2
D3

D4

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

EVALUATION KIT

AVAILABLE

MAX1638

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

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= V

CC

= D4 = +5V, PGND = AGND = D0–D3 = 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)

NDRV, PDRV, DL to PGND.........................-0.3V to (VDD+ 0.3V)

REF, CC1, CC2, LG, D0–D4, 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)

QSOP (derate 8.70mW/°C above +70°C).....................696mW

QSOP θJC..................................................................40°C/W

SSOP (derate 8.00mW/°C above +70°C) .....................640mW

SSOP θ

JC

..................................................................45°C/W

Operating Temperature Range ...........................-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

Over line and load
(Note 1)

I

SINK

= 2mA, VCC= 4.5V

Falling FB, 1% hysteresis with respect to V

REF

Rising FB, 1% hysteresis with respect to V

REF

CSH - CSL =
0mV to 80mV

0µA < I

REF

< 100µA

No load

VCC= VDD= 5.5V, FB forced 200mV 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

%

2

AC Load Regulation
(Note 2)

1

0.5

mA0.5 4.0Reference Short-Circuit Current

V2.7 3.0Reference Undervoltage Lockout

V4.5 5.5Input Voltage Range

%

±1.5

±1

Output Voltage (FB) Accuracy

mV10Reference Load Regulation

V3.465 3.5 3.535Reference Voltage

mA0.1VDDSupply Current

V4.0 4.2Input Undervoltage Lockout

UNITSMIN TYP MAXPARAMETER

CSH - CSL =
0mV to 80mV

%

0.2

DC Load Regulation
(Note 2)

0.1

0.05

TA= +25°C to +85°C
TA= 0°C to +85°C

LG = GND
LG = REF
LG = V

CC

LG = GND
LG = REF
LG = V

CC

2.5FB overdrive = 200mV

5FB overdrive = 0V

Operating
mode

VCC= V

DD

= 5.5V

mA

3.6 10

VCCSupply Current

V

REF

= 0V

Shutdown
mode

0.3DAC code = 11111

ELECTRICAL CHARACTERISTICS (continued)

(VDD= V

CC

= D4 = +5V, PGND = AGND = D0–D3 = 0V, FREQ = REF, TA= 0°C to +85°C, unless otherwise noted.)

MAX1638

_______________________________________________________________________________________

3

DH = DL = 2.5V

VDD= 4.5V

BST - LX = 4.5V

GND (low)

100mV overdrive

FREQ = V

CC

With respect to V

REF

,

FB going low

Minimum

D0–D4 = 0V

D0–D4, VCC= 5.5V

REF (mid)

CSH = CSL = 1.3V, D0–D3 = 5V, D4 = 0V

D0–D4, VCC= 4.5V

CONDITIONS

-2.75 -2 -1.25

V

CC

(high)

ns0 30DH, DL Dead Time

A2DH, DL Source/Sink Current

Ω

0.7 2

Maximum

DH On-Resistance 0.7 2

%

-3 -1

µA100CC2 Source/Sink Current

4 V

CC

V

2.4 3.0

mmho1

kΩ10CC1 Output Resistance

µA±0.1

3.3 3.7

0.2

%85 90Maximum Duty Cycle

LG, FREQ Input Voltage

µA50CSH, CSL Input Current

µA4LG, FREQ Input Current

µA2 5 10D0–D4 Source Current

V2.0Logic Input Voltage High

VCC- 0.1

V

0.8Logic Input Voltage Low

UNITSMIN TYP MAXPARAMETER

FB Input Current

CC2 Clamp Voltage

CC2 Transconductance

PDRV Trip Level

PDRV, NDRV Response Time FB overdrive = 5% ns75
PDRV, NDRV On-Resistance VDD= 4.5V Ω2 5
PDRV, NDRV Source/Sink Current PDRV = NDRV = 2.5V A0.5
PDRV, NDRV Minimum On-Time ns100

FB = 3.5V 85 100 115

Soft-Start Time To full current limit 1 / f

OSC

1536

BST Leakage Current BST = 12V, LX = 7V, REF = GND µA50

V

High-Speed Step-Down Controller with

Synchronous Rectification for CPU Power

ΩDL On-Resistance

NDRV Trip Level

With respect to V

REF

,

FB going high

1.25 2 2.75
%

1 3

TA= +25°C
TA= 0°C to +85°C
TA= +25°C
TA= 0°C to +85°C

Current-Limit Trip Voltage

FB = 0V (Foldback)

mV

15 38 70

V

MAX1638

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

4 _______________________________________________________________________________________

FREQ = REF

FREQ = V

CC

Falling FB, 1% hysteresis with respect to V

REF

Rising FB, 1% hysteresis with respect to V

REF

FREQ = AGND

Over line and load (Note 1)

VCC= V

DD

CONDITIONS

510 600 690

800 1000 1200

Switching Frequency

6 8 10

kHz

240 300 360

%

-8 -6 -4

PWROK Trip Level

%±2.5Output Voltage (FB) Accuracy

V4.5 5.5Input Voltage Range

UNITSMIN TYP MAXPARAMETER

BST - LX = 4.5V

FREQ = V

CC

VDD= 4.5V

Ω0.7 2

%84 90

Ω0.7 2

Maximum Duty Cycle

DL On-Resistance

DH On-Resistance

FB = 3.5VCurrent-Limit Trip Voltage mV70 100 130

ELECTRICAL CHARACTERISTICS

(VDD= VCC= D4 = +5V, PGND = AGND = D0–D3= 0V, FREQ = REF, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)

Note 1: FB accuracy is 100% tested at FB = 3.5V (code 10000) with V

CC

= VDD= 4.5V to 5.5V and CSH - CSL = 0mV to 80mV. The

other DAC codes are tested with V

CC

= VDD= 5V and CSH - CSL = 0.

Note 2: AC load regulation sets the AC loop gain, to make tradeoffs between output filter capacitor size and transient response,

and has only a slight effect on DC accuracy or DC load-regulation error.

Note 3: Specifications from 0°C to -40°C are guaranteed by design, not production tested.

No load V3.448 3.5 3.553Reference Voltage

VCCrising edge, 1% hysteresis V3.9 4.3Input Undervoltage Lockout

0.4

Operating mode 3

VCCSupply Current

VCC= VDD= 5.5V, FB forced 200mV above
regulation point, operating or shutdown mode

mA0.2

VCC= VDD= 5.5V,
FB overdrive =
200mV

VDDSupply Current

mA

12

Shutdown
mode

V

REF

= 0V

DAC code = 11111

MAX1638

High-Speed Step-Down Controller with

Synchronous Rectification for CPU Power

_______________________________________________________________________________________

5

FOLDBACK CURRENT LIMIT

MAX1638-04

VO = 2.0V NOMINAL
A: V

OUT

= 0.5V/div

B: INDUCTOR CURRENT, 5A/div

A

B

10µs/div

START-UP WAVEFORMS

MAX1638-05

A: V

OUT

= 0.5V/div

B: INDUCTOR CURRENT, 5A/div

A

B

400µs/div

1µs/div

SWITCHING WAVEFORMS

C

0

MAX1638-06

VIN = 5V, V

OUT

= 2.5V, LOAD = 5A
A: LX, 5V/div C: INDUCTOR CURRENT,
B: V

OUT

, 20mV/div, AC COUPLED 5A/div

B

A

LOAD-TRANSIENT RESPONSE

WITHOUT GLITCHCATCHER (C

OUT

= 880µF)

MAX1638-01

VIN = 5V, V

OUT

= 2.0V, LOAD = 14A, 3A/µs

A: V

OUT

, 50mV/div, AC COUPLED

B: INDUCTOR CURRENT, 10A/div

A

B

10µs/div

LOAD-TRANSIENT RESPONSE

WITHOUT GLITCHCATCHER (C

OUT

= 440µF)

MAX1638-02

VIN = 5V, V

OUT

= 2.0V, LOAD = 14A, 3A/µs

A: V

OUT

, 100mV/div, AC COUPLED

B: INDUCTOR CURRENT, 10A/div

A

B

10µs/div

LOAD-TRANSIENT RESPONSE

WITH GLITCHCATCHER

MAX1638-03

C

OUT

= 440µF, VIN = 5V, V

OUT

= 2.0V, LOAD = 14A, 30A/µs

A: V

OUT

, 100mV/div, C: NDRV, 5V/div

AC COUPLED D: INDUCTOR CURRENT,

B: PDRV, 5V/div 10A/div

A

D

B

C

10µs/div

__________________________________________Typical Operating Characteristics

(TA = +25°C, using the MAX1638 evaluation kit, unless otherwise noted.)

100

90

30

0.1 10 100

EFFICIENCY vs. OUTPUT CURRENT

50

40

80

70

60

MAX1638-07

OUTPUT CURRENT (A)

EFFICIENCY (%)

1

V

OUT

= 2.0V

V

OUT

= 1.3V

V

OUT

= 3.5V

5.094

1.094

0.001 0.1 10.01 10

REFERENCE VOLTAGE
vs. OUTPUT CURRENT

1.594

2.094

MAX1638-08

OUTPUT CURRENT (mA)

REFERENCE VOLTAGE (V)

2.594

3.594

3.094

4.094

4.594

SOURCING

CURRENT

SINKING

CURRENT

50

55

0

MAXIMUM DUTY CYCLE

vs. SWITCHING FREQUENCY

65
60

70

MAX1638-09

SWITCHING FREQUENCY (kHz)

MAXIMUM DUTY CYCLE (%)

85

95
90

75

80

200 800 1000 1200

100

600400