19-1313; Rev 1; 8/05
KIT
ATION
EVALU
BLE
AVAILA
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
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 synchro-
nous 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 out-
put 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 fea-
tures such as a digitally programmable output;
adjustable transient response; and selectable 0.5%, 1%,
or 2% AC load regulation. Fast recovery from load tran-
sients is ensured by a GlitchCatcher™ current-boost cir-
cuit 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% refer-
ence output.
____________________________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
Typical Operating Circuit
INPUT
+5V
V
CC
AGND
TO V
DD
V
DD
BST
________________________Applications
Pentium Pro™, Pentium II™, PowerPC™, Alpha™,
and K6™ Systems
Workstations
Desktop Computers
LAN Servers
GTL Bus Termination
MAX1638
DH
OUTPUT
1.3V TO 4.5V
LX
PWROK
D0
D1
D2
D3
D4
REF
LG
FREQ
CC1
CC2
FB
DL
PGND
Ordering Information
PART
MAX1638EAG
MAX1638EAG+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
24 SSOP
24 QSOP
CSH
CSL
+Denotes
lead-free package.
Pin Configuration appears at end of data sheet.
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.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
MAX1638
ABSOLUTE MAXIMUM RATINGS
V
DD
, V
CC
, PWROK to AGND ......................................-0.3V to 6V
PGND to AGND ..................................................................±0.3V
CSH, CSL to AGND ....................................-0.3V to (V
CC
+ 0.3V)
NDRV, PDRV, DL to PGND.........................-0.3V to (V
DD
+ 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 (T
A
= +70°C)
QSOP (derate 8.70mW/°C above +70°C) .....................696mW
QSOP
θ
JC
..................................................................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, 10s) .................................+300°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.
ELECTRICAL CHARACTERISTICS
(V
DD
= V
CC
= D4 = +5V, PGND = AGND = D0–D3 = 0V, FREQ = REF,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
Output Voltage (FB) Accuracy
Input Voltage Range
Input Undervoltage Lockout
Over line and load
(Note 1)
V
CC
= V
DD
V
CC
rising edge, 1% hysteresis
V
CC
= V
DD
= 5.5V
Operating
mode
Shutdown
mode
FB overdrive = 200mV
FB overdrive = 0V
DAC code = 11111
V
REF
= 0V
3.6
5
0.3
10
0.1
3.465
2.7
0.5
LG = GND
AC Load Regulation
(Note 2)
CSH - CSL =
0mV to 80mV
LG = REF
LG = V
CC
LG = GND
DC Load Regulation
(Note 2)
PWROK Trip Level
PWROK Output Voltage Low
PWROK Output Current High
Switching Frequency
CSH - CSL =
0mV to 80mV
LG = REF
LG = V
CC
Rising FB, 1% hysteresis with respect to V
REF
Falling FB, 1% hysteresis with respect to V
REF
I
SINK
= 2mA, V
CC
= 4.5V
PWROK = 5.5V
FREQ = V
CC
FREQ = REF
FREQ = AGND
850
540
255
1000
600
300
-7.5
6.5
0.5
1
2
0.05
0.1
0.2
-6
8
-4.5
9.5
0.4
1
1150
660
345
kHz
%
V
µA
%
%
3.5
3.535
10
3.0
4.0
mA
V
mV
V
mA
CONDITIONS
T
A
= +25°C to +85°C
T
A
= 0°C to +85°C
4.5
4.0
MIN
TYP
MAX
±1
±1.5
5.5
4.2
2.5
mA
UNITS
%
V
V
V
CC
Supply Current
V
DD
Supply Current
Reference Voltage
Reference Load Regulation
Reference Undervoltage Lockout
Reference Short-Circuit Current
V
CC
= V
DD
= 5.5V, FB forced 200mV above
regulation point, operating or standby mode
No load
0µA < I
REF
< 100µA
Rising edge, 1% hysteresis
V
REF
= 0V
2
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= V
CC
= D4 = +5V, PGND = AGND = D0–D3 = 0V, FREQ = REF,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
Maximum Duty Cycle
LG, FREQ Input Voltage
Logic Input Voltage Low
Logic Input Voltage High
D0–D4 Source Current
LG, FREQ Input Current
CSH, CSL Input Current
FB Input Current
CC1 Output Resistance
CC2 Transconductance
CC2 Clamp Voltage
CC2 Source/Sink Current
DH On-Resistance
DL On-Resistance
DH, DL Source/Sink Current
DH, DL Dead Time
PDRV Trip Level
NDRV Trip Level
PDRV, NDRV Response Time
PDRV, NDRV On-Resistance
PDRV, NDRV Source/Sink Current
PDRV, NDRV Minimum On-Time
Current-Limit Trip Voltage
Soft-Start Time
BST Leakage Current
FB = 3.5V
FB = 0V (Foldback)
To full current limit
BST = 12V, LX = 7V, REF = GND
85
15
With respect to V
REF
,
FB going low
With respect to V
REF
,
FB going high
FB overdrive = 5%
V
DD
= 4.5V
PDRV = NDRV = 2.5V
T
A
= +25°C
T
A
= 0°C to +85°C
T
A
= +25°C
T
A
= 0°C to +85°C
Minimum
Maximum
100mV overdrive
BST - LX = 4.5V
V
DD
= 4.5V
DH = DL = 2.5V
0
-2.75
-3
1.25
1
75
2
0.5
100
100
38
1536
50
115
70
5
2
2.4
4
100
0.7
0.7
2
30
-2
-1.25
-1
2.75
3
2
2
10
1
3.0
V
CC
CSH = CSL = 1.3V, D0–D3 = 5V, D4 = 0V
FREQ = V
CC
GND (low)
REF (mid)
V
CC
(high)
D0–D4, V
CC
= 4.5V
D0–D4, V
CC
= 5.5V
D0–D4 = 0V
2.0
2
5
10
4
50
±0.1
3.3
V
CC
- 0.1
0.8
V
V
µA
µA
µA
µA
kΩ
mmho
V
µA
Ω
Ω
A
ns
%
%
ns
Ω
A
ns
mV
1 / f
OSC
µA
CONDITIONS
MIN
85
TYP
90
0.2
3.7
V
MAX
UNITS
%
MAX1638
3
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
MAX1638
ELECTRICAL CHARACTERISTICS
(V
DD
= V
CC
= D4 = +5V, PGND = AGND = D0–D3= 0V, FREQ = REF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
Input Voltage Range
Input Undervoltage Lockout
V
CC
Supply Current
V
CC
= V
DD
V
CC
rising edge, 1% hysteresis
V
CC
= V
DD
= 5.5V,
FB overdrive =
200mV
Operating mode
Shutdown
mode
DAC code = 11111
V
REF
= 0V
CONDITIONS
MIN
4.5
3.9
TYP
MAX
5.5
4.3
3
0.4
12
0.2
3.448
-8
6
800
510
240
84
3.5
-6
8
1000
600
300
90
0.7
0.7
70
100
2
2
130
3.553
±2.5
-4
10
1200
690
360
%
Ω
Ω
mV
kHz
mA
V
%
%
UNITS
V
V
V
mA
V
DD
Supply Current
Reference Voltage
Output Voltage (FB) Accuracy
PWROK Trip Level
V
CC
= V
DD
= 5.5V, FB forced 200mV above
regulation point, operating or shutdown mode
No load
Over line and load (Note 1)
Rising FB, 1% hysteresis with respect to V
REF
Falling FB, 1% hysteresis with respect to V
REF
FREQ = V
CC
FREQ = REF
FREQ = AGND
FREQ = V
CC
BST - LX = 4.5V
V
DD
= 4.5V
FB = 3.5V
Switching Frequency
Maximum Duty Cycle
DH On-Resistance
DL On-Resistance
Current-Limit Trip Voltage
Note 1:
FB accuracy is 100% tested at FB = 3.5V (code 10000) with V
CC
= V
DD
= 4.5V to 5.5V and CSH - CSL = 0mV to 80mV. The
other DAC codes are tested with V
CC
= V
DD
= 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.
4
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, using the MAX1638 evaluation kit, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
WITHOUT GLITCHCATCHER (C
OUT
= 880μF)
MAX1638-01
MAX1638
LOAD-TRANSIENT RESPONSE
WITHOUT GLITCHCATCHER (C
OUT
= 440μF)
MAX1638-02
LOAD-TRANSIENT RESPONSE
WITH GLITCHCATCHER
MAX1638-03
A
A
A
B
C
B
10μs/div
V
IN
= 5V, V
OUT
= 2.0V, LOAD = 14A, 3A/μs
A: V
OUT
, 50mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
B
10μs/div
V
IN
= 5V, V
OUT
= 2.0V, LOAD = 14A, 3A/μs
A: V
OUT
, 100mV/div, AC COUPLED
B: INDUCTOR CURRENT, 10A/div
D
10μs/div
C
OUT
= 440μF, V
IN
= 5V, V
OUT
= 2.0V, LOAD = 14A, 30A/μs
C: NDRV, 5V/div
A: V
OUT
, 100mV/div,
AC COUPLED
D: INDUCTOR CURRENT,
B: PDRV, 5V/div
10A/div
FOLDBACK CURRENT LIMIT
MAX1638-04
STARTUP WAVEFORMS
MAX1638-05
SWITCHING WAVEFORMS
MAX1638-06
A
A
B
A
C
B
10μs/div
V
O
= 2.0V NOMINAL
A: V
OUT
= 0.5V/div
B: INDUCTOR CURRENT, 5A/div
B
400μs/div
A: V
OUT
= 0.5V/div
B: INDUCTOR CURRENT, 5A/div
0
1μs/div
V
IN
= 5V, V
OUT
= 2.5V, LOAD = 5A
A: LX, 5V/div
C: INDUCTOR CURRENT,
5A/div
B: V
OUT
, 20mV/div, AC COUPLED
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.5V
MAX1638-07
REFERENCE VOLTAGE
vs. OUTPUT CURRENT
MAX1638-08
MAXIMUM DUTY CYCLE
vs. SWITCHING FREQUENCY
95
MAXIMUM DUTY CYCLE (%)
90
85
80
75
70
65
60
55
50
MAX1638-09
100
90
80
EFFICIENCY (%)
70
60
50
40
30
0.1
1
V
OUT
= 2.0V
5.094
4.594
REFERENCE VOLTAGE (V)
4.094
3.594
3.094
2.594
2.094
1.594
1.094
0.001
SOURCING
CURRENT
SINKING
CURRENT
100
V
OUT
= 1.3V
10
100
0.01
0.1
1
10
0
200
400
600
800
1000
1200
OUTPUT CURRENT (A)
OUTPUT CURRENT (mA)
SWITCHING FREQUENCY (kHz)
_______________________________________________________________________________________
5
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