Rainbow Electronics MAX1625 User Manual

_______________General Description

The MAX1624/MAX1625 are ultra-high-performance,
step-down DC-DC controllers 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, they deliver
over 35A from 1.1V 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. These controllers achieve over 90% effi­ciency by using synchronous rectification. Flying-capaci­tor bootstrap circuitry drives inexpensive, external
N-channel MOSFETs.

The switching frequency is resistor programmable from
100kHz to 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 MAX1624 is available in a 24-pin SSOP and offers
additional features such as a digitally programmable out­put in 100mV increments; adjustable transient response;
selectable 0.5%, 1%, or 2% AC load regulation; and gate
drive for a current-boost MOSFET. The MAX1625 is resis­tor adjustable and comes in a 16-pin narrow SO pack­age. Other features in both controllers include internal
digital soft-start, a power-good output, and a 3.5V ±1%
reference output. For a similar controller compatible with
the latest Intel V

RM/VID

specification, see the MAX1638*

data sheet.

________________________Applications

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

Desktop Computers
LAN Servers
Industrial Computers
GTL Bus Termination

____________________________Features

♦ Better than ±1% Output Accuracy Over

Line and Load

♦ 90% Efficiency
♦ Excellent Transient Response
♦ Resistor-Programmable Fixed Switching

Frequency from 100kHz to 1MHz

♦ Over 35A Output Current
♦ Digitally Programmable Output from 1.1V to 3.5V

in 100mV Increments (MAX1624)

♦ Resistor-Adjustable Output down to 1.1V

(MAX1625)

♦ Remote Sensing
♦ Adjustable AC Loop Gain (MAX1624)
♦ GlitchCatcher™ Circuit for Fast Load-Transient

Response (MAX1624)

♦ Power-Good (PWROK) Output
♦ Current-Mode Feedback
♦ Digital Soft-Start
♦ Strong 2A Gate Drivers
♦ Current-Limited Output

MAX1624/MAX1625

High-Speed Step-Down Controllers with

Synchronous Rectification for CPU Power

________________________________________________________________

Maxim Integrated Products

1

19-1227; Rev 1; 6/97

PART

MAX1624EAG
MAX1625ESE

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

24 SSOP
16 Narrow SO

______________Ordering Information

__________Typical Operating Circuit

Pin Configurations appear at end of data sheet.

*

Future product.
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.

EVALUATION KIT

AVAILABLE

V

CC

FREQ
CC2
CC1

REF

AGND

(SIMPLIFIED)

FB

DL

DH

PWROK

BST

CSL

CSH

LX

TO V

DD

TO AGND

PGND

OUTPUT

1.1V TO 4.5V

INPUT

+5V

V

DD

N

N

MAX1625

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

kHz

MAX1624/MAX1625

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

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= V

CC

= D4 = +5V, PGND = AGND = D0–D3 = 0V, R

FREQ

= 33.3kΩ, 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)

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

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

Operating Temperature Range

MAX162_E_ _.......................................................-40°C to +85°C

Storage Temperature Range.............................-65°C to +125°C

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

R

FREQ

= 33.3kΩ

R

FREQ

= 20kΩ

PWROK = 5.5V

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

I

SINK

= 2mA, VCC= 4.5V

Falling FB, 1% hysteresis with respect to V

REF

VCCrising edge, 1% hysteresis

Rising FB, 1% hysteresis with respect to V

REF

VCC= V

DD

MAX1624, over line
and load (Note 1)

V

REF

= 0V

Rising edge, 1% hysteresis

0µA < I

LOAD

< 100µA

VCC= VDD= 5.5V, FB overdrive = 200mV,
operating or standby mode

MAX1625, over line
and load (Note 2)

No load

CONDITIONS

540 600 660

850 1000 1150

Switching Frequency

µA1PWROK Output Current High

V0.4PWROK Output Voltage Low

6.5 8 9.5

%

-7.5 -6 -4.5

PWROK Trip Level

1

2

1

%

0.5

AC Load Regulation
(Note 3)

±1.5

%

±1

FB Set Voltage

±1.5

2.5

VCCSupply Current

V4.0 4.2

V4.5 5.5Input Voltage Range

Input Undervoltage Lockout

%

±1

FB Accuracy

mA0.5 4.0Reference Short-Circuit Current

V2.7 3.0Reference Undervoltage Lockout

mV10Reference Load Regulation

mA

0.3
mA0.1VDDSupply Current

V3.465 3.5 3.535Reference Voltage

UNITSMIN TYP MAXPARAMETER

Operating mode
Standby mode

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

CSH - CSL =
0mV to 80mV

R

FREQ

= 200kΩ

kHz

85 100 115

LG = REF

LG = GND

LG = V

CC

MAX1624

MAX1625

LG = REF

CSH - CSL =
0mV to 80mV

LG = GND

LG = V

CC

0.1

MAX1624

MAX1625

0.2

0.1
%

0.05

DC Load Regulation
(Note 3)

ELECTRICAL CHARACTERISTICS (continued)

(VDD= V

CC

= D4 = +5V, PGND = AGND = D0–D3 = 0V, R

FREQ

= 33.3kΩ, TA= 0°C to +85°C, unless otherwise noted.)

MAX1624/MAX1625

_______________________________________________________________________________________

3

DH = DL = 2.5V

VDD= 4.5V

BST - LX = 4.5V

LG = GND (low)

100mV overdrive

R

FREQ

= 20kΩ

With respect to V

REF

,

FB going low

Minimum

MAX1625, CSH = CSL = 1.1V

D0–D4 = 0V, 5V

D0–D4; VCC= 4.5V

LG = REF (mid)

MAX1624, CSH = CSL = 1.3V,
D0–D3 = 5V, D4 = 0V

D0–D4; VCC= 5.5V

CONDITIONS

-2.75 -2 -1.25

LG = V

CC

(high)

ns0 30

FB = 1.1V

DH, 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

50

3.3 3.7

0.2

%85 90Maximum Duty Cycle

LG Input Voltage

µA

50

CSH, CSL Input Current

µA4LG Input Current

µA±1D0–D4 Input Current

V2.0Logic Input Voltage High

VCC- 0.2

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
Current-Limit Trip Voltage mV85 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 Controllers 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

mA

MAX1624/MAX1625

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

4 _______________________________________________________________________________________

R

FREQ

= 33.3kΩ

R

FREQ

= 20kΩ

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

Falling FB, 1% hysteresis with respect to V

REF

VCCrising edge, 1% hysteresis

Rising FB, 1% hysteresis with respect to V

REF

VCC= V

DD

R

FREQ

= 200kΩ

Operating mode

VCC= VDD= 5.5V, FB overdrive = 200mV,
operating or standby mode

MAX1624, over line and load

No load

CONDITIONS

510 600 690

Standby mode

800 1000 1200

Switching Frequency

6 8 10

kHz

80 100 120

%

-8 -6 -4

PWROK Trip Level

±2.5

3

VCCSupply Current

V3.9 4.3

V4.5 5.5Input Voltage Range

Input Undervoltage Lockout

%±2.5FB Accuracy

mA

0.4
mA0.2VDDSupply Current

V3.447 3.5 3.553Reference Voltage

UNITSMIN TYP MAXPARAMETER

MAX1625FB Set Voltage

BST - LX = 4.5V

R

FREQ

= 20kΩ

VDD= 4.5V

Ω0.7 2

%84 90

Ω0.7 2

Maximum Duty Cycle

DL On-Resistance

DH On-Resistance

Current-Limit Trip Voltage mV70 100 130

ELECTRICAL CHARACTERISTICS

(VDD= VCC= D4 = +5V, PGND = AGND = D0–D3= 0V, R

FREQ

= 33.3kΩ, TA= -40°C to +85°C, unless otherwise noted.) (Note 4)

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 at the major transition points with V

CC

= VDD= 5V and CSH - CSL = 0. FB accuracy at other

DAC codes over line and load is guaranteed by design.

Note 2: FB set voltage is 100% tested with VCC= VDD= 4.5V to 5.5V and CSH - CSL = 0mV to 80mV.
Note 3: 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 4: Specifications from 0°C to -40°C are not production tested.

%

MAX1624/MAX1625

High-Speed Step-Down Controllers with

Synchronous Rectification for CPU Power

_______________________________________________________________________________________ 5

__________________________________________Typical Operating Characteristics

(TA = +25°C, using the MAX1624 evaluation kit, unless otherwise noted.)

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE DETAIL

(WITH GLITCHCATCHER)

(1.1V)

C

D

MAX1624/25 TOC01

A: PDRV, 5V/div
B: V

OUT

, 50mV/div, AC COUPLED
C: NDRV, 5V/div
D: LOAD CURRENT, 0A TO 10A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE

(WITH GLITCHCATCHER)

(1.1V )

C

MAX1624/25 TOC02

A: V

OUT

, 50mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
C: LOAD CURRENT, 0A TO 10A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE

(WITHOUT GLITCHCATCHER)

(1.1V)

C

MAX1624/25 TOC03

A: V

OUT

, 50mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
C: LOAD CURRENT, 0A TO 10A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE

(WITHOUT GLITCHCATCHER)

(3.5V)

C

MAX1624/25 TOC15

A: V

OUT

, 100mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
C: LOAD CURRENT, 0A TO 11A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE

(WITH GLITCHCATCHER)

(2.5V)

C

MAX1624/25 TOC17

A: V

OUT

, 50mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
C: LOAD CURRENT, 0A TO 10A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE

(WITHOUT GLITCHCATCHER)

(2.5V)

C

MAX1624/25 TOC18

A: V

OUT

, 50mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
C: LOAD CURRENT, 0A TO 10A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

10µs/div

MAX1624

LOAD-TRANSIENT RESPONSE

(WITH GLITCHCATCHER)

(3.5V)

C

MAX1624/25 TOC16

A: V

OUT

, 100mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
C: LOAD CURRENT, 0A TO 11A, t

RISE

= t

FALL

= 100ns

B

A

LG = REF

1µs/div

MAX1624

SWITCHING WAVEFORMS

C

0

MAX1624/25 TOC10

VIN = 5V, V

OUT

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

OUT

, 20mV/div, AC COUPLED

C: INDUCTOR CURRENT, 5A/div

B

A

1ms/div

MAX1624

STARTUP AND STANDBY RESPONSE

C

MAX1624/25 TOC11

VIN = 5V, V

OUT

= 2.5V, LOAD = 13.8A

A: V

OUT

, 1V/div
B: INDUCTOR CURRENT, 10A/div
C: STANDBY, D0–D4

B

A

MAX1624/MAX1625

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

6 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, using the MAX1624 evaluation kit, unless otherwise noted.)

100

0

0.1 1 10

MAX1624

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 1.1V)

20
10

MAX1624/25 TOC04

OUTPUT CURRENT (A)

EFFICIENCY (%)

40
30

60

70

50

80

90

100

0

0.1 1 10

MAX1624

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 2.5V)

20
10

MAX1624/25 TOC05

OUTPUT CURRENT (A)

EFFICIENCY (%)

40
30

60

70

50

80

90

100

0

0.1 1 10

MAX1624

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 3.5V)

20
10

MAX1624/25 TOC06

OUTPUT CURRENT (A)

EFFICIENCY (%)

40
30

60

70

50

80

90

MAX1624/MAX1625

High-Speed Step-Down Controllers with

Synchronous Rectification for CPU Power

_______________________________________________________________________________________ 7

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, using the MAX1624 evaluation kit, unless otherwise noted.)

1.1020

1.1000

0.1 10.01 10

MAX1624

OUTPUT VOLTAGE vs. OUTPUT CURRENT

(V

OUT

= 1.1V)

1.1002

1.1006

1.1004

MAX1624/25 TOC07

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

1.1008

1.1010

1.1014

1.1012

1.1016

1.1018

LG = V

CC

LG = REF

LG = AGND

R9 AND R10 = 4.7Ω

2.500

2.490

0.1 10.01 10

MAX1624

OUTPUT VOLTAGE vs. OUTPUT CURRENT

(V

OUT

= 2.5V)

2.491

2.492

MAX1624/25 TOC08

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

2.493

2.494

2.496

2.495

2.497

2.498

2.499

LG = V

CC

LG = REF

LG = AGND

R9 AND R10 = 4.7Ω

3.500

3.480

0.1 10.01 10

MAX1624

OUTPUT VOLTAGE vs. OUTPUT CURRENT

(V

OUT

= 3.5V)

3.482

3.486

3.484

MAX1624/25 TOC09

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

3.488

3.494

3.490

3.492

3.496

3.498

LG = V

CC

LG = REF

LG = AGND

R9 AND R10 = 4.7Ω

5.094

1.094

0.001 0.1 10.01 10

REFERENCE VOLTAGE
vs. OUTPUT CURRENT

1.594

2.094

MAX1624/25 TOC12

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

MAX1624/25 tTOC13

SWITCHING FREQUENCY (kHz)

MAXIMUM DUTY CYCLE (%)

85

95
90

75

80

200 800 1000 1200

100

600400

10

-10

1.7 2.3 2.91.1 3.5

MAX1624

OUTPUT ERROR vs.

DAC OUTPUT VOLTAGE SETTING

-8

-4

-6

MAX1624/25 TOC19

DAC OUTPUT VOLTAGE SETTING (V)

OUTPUT ERROR (mV)

-2

4

0

2

6

8

MAX1624/MAX1625

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

8 _______________________________________________________________________________________

MAX1625MAX1624

PIN

High-Side Main MOSFET Switch Gate-Drive Output. DH is a floating driver output that
swings from LX to BST, riding on the LX switching-node voltage. See the section

BST

High-Side Gate-Driver Supply and MOSFET Drivers

.

DH1624

Switching Node. Connect LX to the high-side MOSFET source and inductor.LX1523

Power GroundPGND1422

DL

Low-Side Synchronous Rectifier Gate-Drive Output. DL swings between PGND and VDD.
See the section

BST High-Side Gate-Driver Supply and MOSFET Drivers

.

1321

V

DD

5V Power Input for MOSFET Drivers. Bypass VDDto PGND within 0.2 in. (5mm) of the
VDDpin using a 0.1µF capacitor and 4.7µF capacitor connected in parallel.

1220

PDRV GlitchCatcher P-Channel MOSFET Driver Output. PDRV swings between VDDand PGND. —19

NDRV

GlitchCatcher N-Channel MOSFET Driver Output. NDRV swings between VDDand
PGND.

—18

D4, D3 Digital Inputs for Programming the Output Voltage —16, 17

FREQ

Frequency-Programming Input. Attach a resistor within 0.2 in. (5mm) of FREQ to AGND to
set the switching frequency between 100kHz and 1MHz. The FREQ pin is normally 2V DC.

1115

CC2

Slow-Loop Compensation Capacitor Input. Connect a ceramic capacitor from CC2 to
AGND. See the section

Compensating the Feedback Loop.

1014

BST

Boost-Capacitor Bypass for High-Side MOSFET Gate Drive. Connect a 0.1µF capacitor
and low-leakage Schottky diode as a bootstrapped charge-pump circuit to derive a 5V
gate drive from V

DD

for DH.

11

NAME FUNCTION

______________________________________________________________Pin Description

CC1

Fast-Loop Compensation Capacitor Input. Connect a ceramic capacitor and resistor in
series from CC1 to AGND. See the section

Compensating the Feedback Loop

.

913

FB

Voltage-Feedback Input.
MAX1624: Connect FB to the CPU’s remote voltage-sense point. The voltage at this
input is regulated to a value determined by D0–D4.
MAX1625: Connect a feedback resistor voltage divider close to FB from the output to
AGND. FB is regulated to 1.1V.

812

PWROK

Open-Drain Logic Output. PWROK is high when the voltage on FB is within +8% and -6%
of its setpoint.

22

CSL

Current-Sense Amplifier’s Inverting Input. Place the current-sense resistor very close to
the controller IC, and use a Kelvin connection. Use an RC filter network at CSL (Figure 1).

33

CSH Current-Sense Amplifier’s Noninverting Input. Use an RC filter network at CSH (Figure 1).44

D2, D1,D0Digital Inputs for Programming the Output Voltage. D0–D4 are logic inputs that set the

output to a voltage between 1.1V and 3.5V in 100mV increments.

—5, 6, 7

LG

Loop Gain-Control Input. LG is a three-level input that is used to trade off loop gain vs.
AC load-regulation and load-transient response. Connect LG to VCC, REF, or AGND for
2%, 1%, or 0.5% AC load-regulation errors, respectively.

—8

V

CC

Analog Supply Input, 5V. Use an RC filter network, as shown in Figure 1. 59

REF

Reference Output, 3.5V. Bypass REF to AGND with 0.1µF (min). Sources up to 100µA for
external loads. Force REF below 2V to turn off the controller.

610

AGND Analog Ground711