National P/N LM2636 - 5-Bit Programmable Synchronous Buck Regulator Controller
LM2636MTC
Full
production
N/A
1K+
$1.6000
rail
of
73
[logo]UZ2T
LM2636
MTC
LM2636MTCX
Full
production
N/A
1K+
$1.6000
reel
of
2500
[logo]UZ2T
LM2636
MTC
LM2636 MDC
Full
production
N/A
tray
of
N/A
-
LM2636 MWC
Full
production
N/A
wafer
jar
of
N/A
-
General Description
The LM2636 is a high speed controller designed specifically for use in synchronous DC/DC buck converters
for advance d microprocessors. A 5-bit DAC accepts the VID code directly from the CPU and adjusts the
output voltage from 1.3V to 3.5V. It provides the power good, over-voltage protection, and output enable
features as required by Intel VRM specifications. Current limiting is achieved by monitoring the voltage drop
across the rDS_ON of the high side MOSFET, which eliminates an expensive current sense resistor.
The LM2636 employs a fixed-frequency voltage mode PWM architecture. To provide a faster response to a
large and fast load transient, two ultra-fast comparators are built in to monitor the output voltage and
override the primary control loop when necessary. The PWM frequency is adjustable from 50 kHz to 1 MHz
through an external resistor. The wide range of PWM frequency gives the power supply designer the
flexibility to make trade-offs between load transient response performance, MOSFET cost and the overall
efficiency. The adaptive non-overlapping MOSFET gate drivers help avoid any potential shoot-through
problem while maintaining high efficiency. BiCMOS gate drivers with rail-to-rail swing ensure that no
spurious turn-on occur. When only 5V is available, a bootstrap structure can be employed to accommodate
an NMOS high side switch. The precision reference trimmed to 2.5% over temperature is available externally
for use by other regulators. Dynamic positioning of load voltage, which helps cut the number of output
capacitors, can also be implemented easily.
Features
q
1.3V to 3.5V 5-bit programmable output voltage
q
Synchronous rectification
q
Power Good flag and output enable
q
Over-voltage protection
q
Initial Output Accuracy: 1.5% over temperature
q
Current limit without external sense resistor
q
Adaptive non-overlapping MOSFET gate drives
q
Adjustable switching frequency: 50 kHz to 1 MHz
q
Dynamic output voltage positioning
q
1.256V reference voltage available externally
q
Plastic SO-20 package and TSSOP-20 package
Applications
q
Motherboard power supply/VRM for Cyrix Gxm, Cyrix Gxi, Cyrix MII, Pentium II, Pentium Pro, 6x86
and K6 processors
q
5V to 1.3V-3.5V high current power supplies
file:///H|/imaging/BITTING/cpl/20020808_1/08062002_10/NATL/08062002_HTML/LM2636.html (2 of 3) [Aug-09-2002 2:37:51 PM]