19-1337; Rev 1; 8/05
NUAL
KIT MA
ATION
ET
EVALU
TA SHE
WS DA
FOLLO
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
____________________________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
________________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 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.
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. The MAX1639 is available in a 16-pin
narrow SOIC package.
MAX1639
________________________Applications
Local DC-DC Converters for CPUs
Workstations
Desktop Computers
LAN Servers
GTL Bus Termination
__________ Typical Operating Circuit
INPUT
+5V
V
CC
AGND
TO V
DD
V
DD
BST
MAX1639
DH
LX
PWROK
OUTPUT
1.1V TO 4.5V
_______________Ordering Information
PART
MAX1639ESE
MAX1639ESE+
TEMP RANGE
40°C to +85°C
40°C to +85°C
PIN-PACKAGE
16 Narrow SO
16 Narrow SO
REF
DL
PGND
CSH
CSL
+Denotes
lead-free packages.
FREQ
Pin Configuration appears at end of data sheet.
CC1
CC2
FB
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
MAX1639
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)
DL to PGND................................................-0.3V to (V
DD
+ 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 (T
A
= +70°C)
16-Pin Narrow SO (derate 8.70mW/°C above +70°C) ....696mW
SO
θ
JC
...........................................................................65°C/W
Operating Temperature Range
MAX1639ESE....................................................-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
= +5V, PGND = AGND = 0V, FREQ = REF,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
FB Voltage
Input Voltage Range
Input Undervoltage Lockout
CONDITIONS
Includes line and load
regulation errors
V
CC
= V
DD
V
CC
rising edge, 1% hysteresis
V
CC
= V
DD
= 5.5V
Operating
mode
Shutdown
mode
FB overdrive = 60mV
FB overdrive = 0V
V
REF
= 0V
5
3.6
10
0.1
3.465
2.7
0.5
1
0.1
-7.5
6.5
-6
8
-4.5
9.5
0.4
1
850
540
255
85
3.3
V
CC
- 0.1
1000
600
300
90
0.2
3.7
V
1150
660
345
%
kHz
3.5
3.535
10
3.0
4.0
mA
V
mV
V
mA
%
%
%
V
µA
T
A
= +25°C to +85°C
T
A
= 0°C to +85°C
MIN
1.089
1.083
4.5
4.0
TYP
MAX
1.111
1.117
5.5
4.2
2.5
mA
UNITS
V
V
V
V
CC
Supply Current (I
CC
)
V
DD
Supply Current (I
DD
)
Reference Voltage
Reference Load Regulation
Reference Undervoltage Lockout
Reference Short-Circuit Current
AC Load Regulation
DC Load Regulation
PWROK Trip Level
PWROK Output Voltage Low
PWROK Output Current High
Switching Frequency
Maximum Duty Cycle
FREQ Input Voltage
FREQ Input Voltage
V
CC
= V
DD
= 5.5V, FB forced 60mV above
regulation point, operating or standby mode
No load
0µA < I
REF
< 100µA
Rising edge, 1% hysteresis
V
REF
= 0V
CSH - CSL = 0mV to 80mV
CSH - CSL = 0mV to 80mV
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
FREQ = V
CC
GND (low)
REF (mid)
V
CC
(high)
2
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
MAX1639
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= V
CC
= +5V, PGND = AGND = 0V, FREQ = REF,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
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
Current-Limit Trip Voltage
Soft-Start Time
BST Leakage Current
FB = 1.1V
FB = 0V (foldback)
To full current limit
BST = 12V, LX = 7V, REF = GND
Minimum
Maximum
30mV overdrive
BST - LX = 4.5V
V
DD
= 4.5V
DH = DL = 2.5V
0
85
15
2.4
4
100
0.7
0.7
2
30
100
38
1536
50
115
70
2
2
10
1
3.0
V
CC
CSH = CSL = 1.1V
CONDITIONS
MIN
TYP
MAX
4
50
±0.1
UNITS
µA
µA
µA
kΩ
mmho
V
µA
Ω
Ω
A
ns
mV
1 / f
OSC
µA
ELECTRICAL CHARACTERISTICS
(V
DD
= V
CC
= +5V, PGND = AGND = 0V, FREQ = REF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Range
Input Undervoltage Range
V
DD
Supply Current
V
DD
Supply Current
Reference Voltage
FB Voltage
PWROK Trip Level
V
CC
= V
DD
V
CC
rising edge, 1% hysteresis
V
CC
= V
DD
=
5.5V
Operating mode
Shutdown mode
FB overdrive = 60mV
VREF = 0V
CONDITIONS
MIN
4.5
3.9
TYP
MAX
5.5
4.3
3
12
0.2
3.448
1.072
-8
6
800
510
240
84
2
2
70
130
3.553
1.128
-4
10
1200
690
360
%
Ω
Ω
mV
kHz
UNITS
V
V
mA
mA
V
V
%
V
CC
= V
DD
= 5.5V, FB forced 60mV above
regulation point, operating or shutdown mode
No load
Includes line and load regulation errors
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 = 1.1V
Switching Frequency
Maximum Duty Cycle
DH On-Resistance
DL On-Resistance
Current-Limit Trip Voltage
Note 1:
Specifications from 0°C to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
MAX1639
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, using the MAX1639 evaluation kit, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
(V
OUT
= 2.5V)
MAX1639-01
FOLDBACK CURRENT LIMIT
(V
OUT
= 2.5V, NOMINAL)
MAX1639-02
STARTUP WAVEFORMS
MAX1639-03
A
A
A
B
B
10µs/div
V
IN
= 5V, V
OUT
= 2.5V, LOAD = 8A
A: V
OUT
, 100mV/div, AC COUPLED
B: INDUCTOR CURRENT, 5A/div
10µs/div
A: V
OUT
= 0.5V/div
B: INDUCTOR CURRENT, 5A/div
B
400µs/div
A: INDUCTOR CURRENT, 2A/div
B: V
OUT
= 1V/div
SWITCHING WAVEFORMS
MAX1639-04
EFFICIENCY vs. OUTPUT CURRENT
MAX1639-05
MAXIMUM DUTY CYCLE
vs. SWITCHING FREQUENCY
95
MAXIMUM DUTY CYCLE (%)
90
85
80
75
70
65
60
55
MAX1639-06
100
3.5V
90
EFFICIENCY (%)
2.5V
80
1.8V
70
100
A
B
C
0
60
50
1µs/div
V
IN
= 5V, V
OUT
= 2.5V, LOAD = 0A
A: V
OUT
, 20mV/div
B: INDUCTOR CURRENT, 2A/div
C: LX, 5V/div
0.1
1
OUTPUT CURRENT (A)
10
50
0
200
400
600
800
1000
1200
SWITCHING FREQUENCY (kHz)
4
_______________________________________________________________________________________
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
______________________________________________________________Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
NAME
BST
PWROK
CSL
CSH
V
CC
REF
AGND
FB
CC1
CC2
FUNCTION
Boost-Capacitor Bypass for High-Side MOSFET Gate Drive. Connect a 0.1µF capacitor and low-leak-
age Schottky diode as a bootstrapped charge-pump circuit to derive a 5V gate drive from V
DD
for DH.
Open-Drain Logic Output. PWROK is high when the voltage on FB is within +8% and -6% of its set-
point.
Current-Sense Amplifier’s Inverting Input. Place the current-sense resistor very close to the controller IC,
and use a Kelvin connection.
Current-Sense Amplifier’s Noninverting Input
Analog Supply Input, 5V. Use an RC filter network, as shown in Figure 1.
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.
Analog Ground
Voltage-Feedback Input. The voltage at this input is regulated to 1.100V.
Fast-Loop Compensation Capacitor Input. Connect a ceramic capacitor and resistor in series from
CC1 to AGND. See the section
Compensating the Feedback Loop.
Slow-Loop Compensation Capacitor Input. Connect a ceramic capacitor from CC2 to AGND. See the
section
Compensating the Feedback Loop.
Frequency-Select Input. FREQ = V
CC
: 1MHz
FREQ = REF: 600kHz
FREQ = AGND: 300kHz
Power Input for MOSFET Drivers, 5V. Bypass V
DD
to PGND within 0.2 in. (5mm) of the V
DD
pin using a
0.1µF capacitor and 4.7µF capacitor connected in parallel.
Low-Side Synchronous Rectifier Gate-Drive Output. DL swings between PGND and V
DD
. See the
section
BST High-Side Gate-Driver Supply and MOSFET Drivers.
Power Ground
Switching Node. Connect LX to the high-side MOSFET source and inductor.
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.
MAX1639
11
FREQ
12
13
14
15
16
V
DD
DL
PGND
LX
DH
_______________________________________________________________________________________
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