lm2637mx National Semiconductor Corporation, lm2637mx Datasheet - Page 8

• Manufacturer Part Number: lm2637mx
• Description: Motherboard Power Supply Solution With A 5-bit Programmable Switching Controller And Two Linear Regulator Controllers
• Manufacturer: National Semiconductor Corporation

www.national.com
Pin Description
Preferred Startup Timing
Note: See Start Up section in Application Information.
Applications Information
OVERVIEW
The LM2637 provides control and protection for three volt-
age regulators. Namely, a synchronous buck switching con-
troller and two linear regulator controllers that drive an ex-
ternal N-FET or NPN transistor.
Pin
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1
2
3
4
5
6
7
8
9
LG
PGND
V
SNS2
G2
SGND
V
SNS1
CS+
CS−
OVP
FREQ
EAO
FB
PWGD
VID4
VID3
VID2
VID1
VID0
G3
SNS3
EN
HG
DD
CC
Pin Name
Low side N-FET gate driver output.
Ground for the two FET drivers of the switching section.
Supply for the FET gate drivers. Usually tied to +12V.
Feedback pin for the 1.5V linear regulator.
Gate drive output for the external N-MOS of the fast 1.5V linear regulator.
Ground for internal signal circuitry and system ground reference.
Supply voltage. Usually +5V.
Output voltage monitor input for the switching regulator.
Switching regulator current sense input, positive node.
Switching regulator current sense input, negative node.
Over-voltage protection output for the switching regulator. Can be used to fire an external
SCR.
Switching frequency adjustment pin. An external resistor is needed to set the desired
frequency.
Output of the error amplifier. Used for compensating the switching regulator.
Inverting input of the error amplifier. Used for compensating the switching regulator.
Open collector Power Good signal.
5-Bit DAC input, MSB.
5-Bit DAC input.
5-Bit DAC input.
5-Bit DAC input.
5-Bit DAC input, LSB.
Gate drive pin for the external N-MOS of the 2.5V linear regulator.
Feedback pin for the 2.5V linear regulator.
Output Enable. A logic low shuts the whole chip down.
High side N-FET gate driver output.
8
Switching Section — The switching controller features a
VRM-compatible, 5-bit programmable output voltage, over-
current and over-voltage protection, under-voltage latch-off,
a power good signal, and an output enable. The 5-bit DAC
has a typical tolerance of 1%. There are two user-selectable
over-current protection methods. One provides accurate
over-current protection with the use of an external sense
resistor. The other saves cost by taking advantage of the
r
DS_ON
Pin Function
of the high-side FET. The over-voltage protection
10084831