LM2639 5-Bit Programmable, High Frequency Multi-phase PWM Controller
February 2000
LM2639
5-Bit Programmable, High Frequency Multi-phase PWM
Controller
General Description
The LM2639 provides an attractive solution for power sup-
plies of high power microprocessors (such as Pentium II
™
,
M II
™
, K6
™
-2, K6
™
-3, etc.) exhibiting ultra fast load tran-
sients. Compared to a conventional single-phase supply, an
LM2639 based multi-phase supply distributes the thermal
and electrical loading among components in multiple phases
and greatly reduces the corresponding stress in each com-
ponent. The LM2639 can be programmed to control either a
3-phase converter or a 4-phase converter. Phase shift
among the phases is 120˚ in the case of three phase and 90˚
with four-phase. Because the power channels are out of
phase, there can be significant ripple cancellation for both
the input and output current, resulting in reduced input and
output capacitor size. Due to the nominal operating fre-
quency of 2 MHz per phase, the size of the output inductors
can be greatly reduced which results in a much faster load
transient response and a dramatically shrunk output capaci-
tor bank. Microprocessor power supplies with all surface
mount components can be easily built.
The internal high speed transconductance amplifier guaran-
tees good dynamic performance. The output drive voltages
can be adjusted through a resistor divider to control switch-
ing loss in the external FETs.
The internal master clock frequency of up to 8 MHz is set by
an external reference resistor. An external clock of 10 MHz
can also be used to drive the chip to achieve frequency con-
trol and multi-chip operation.
The LM2639 also provides input under-voltage lock-out with
hysteresis and input over-current protection.
Features
n
n
n
n
n
n
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n
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Ultra fast load transient response
Enables all surface-mount-design
Selectable 2, 3, 4 phase operation
Clock frequency from 40 kHz to 10 MHz
Precision load current sharing
5-bit programmable from 3.5V to 1.3V
VID code compatible to VRM 8.X specification
Output voltage is 2.0V for VID code 11111
Selectable internal or external clock
Digital 16-step soft start
Input under-voltage lock-out, over-current protection
Applications
n
Servers and workstations
n
High current, ultra-fast transient microprocessors
Pin Configuration
24-Pin Plastic SOIC
DS101143-1
Top View
See NS Package Number M24B
M II
™
is a trademark of Cyrix Corporation a wholly owned subsidiary of National Semiconductor Corporation.
Pentium II
™
is a trademark of Intel Corporation.
K6
™
is a trademark of Advanced Micro Devices, Inc.
© 2000 National Semiconductor Corporation
DS101143
www.national.com
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