LM3311
Step-Up PWM DC/DC Converter with Integrated LDO,
Op-Amp, and Gate Pulse Modulation Switch
General Description
The LM3311 is a step-up DC/DC converter integrated with
an LDO, an Operational Amplifier, and a gate pulse modu-
lation switch. The boost (step-up) converter is used to gen-
erate an adjustable output voltage and features a low R
DSON
internal switch for maximum efficiency. The operating fre-
quency is selectable between 660kHz and 1.28MHz allowing
for the use of small external components. An external soft-
start pin enables the user to tailor the soft-start time to a
specific application and limit the inrush current. The LDO
also has an adjustable output voltage and is stable using
ceramic output capacitors. The Op-Amp is capable of
sourcing/sinking 135mA of current (typical). The gate pulse
modulation switch can operate with a VGH voltage of 5V to
30V. The LM3311 is available in a low profile 24-lead LLP
package.
Features
n
Boost converter with a 2A, 0.18
switch
n
Boost output voltage adjustable up to 20V
n
Operating voltage range of 2.5V to 7V
n
660kHz/1.28MHz pin selectable switching frequency
n
Adjustable soft-start function
n
Input undervoltage protection
n
Over temperature protection
n
Adjustable low dropout linear regulator (LDO)
n
Integrated Op-Amp
n
Integrated gate pulse modulation (GPM) switch
n
24-Lead LLP package
Applications
n
TFT Bias Supplies
n
Portable Applications
Typical Application Circuit
20126331
September 2005
LM331
1
Step-Up
PWM
DC/DC
Converter
with
Integrated
LDO,
Op-Amp,
and
Gate
Pulse
Modulation
Switch
2005 National Semiconductor Corporation
DS201263
www.national.com
Connection Diagram
20126304
LLP-24 (Top View)
JA
=37C/W
Ordering Information
Order Number
Spec.
Package
Type
NSC Package Drawing
Supplied As
LM3311SQ
LLP-24
SQA24A
1000 units/reel
tape and reel
LM3311SQX
LLP-24
SQA24A
4500 units/reel
tape and reel
LM3311SQ
NOPB
LLP-24
SQA24A
1000 units/reel
tape and reel
LM3311SQX
NOPB
LLP-24
SQA24A
4500 units/reel
tape and reel
Pin Descriptions
Pin
Name
Function
1
NC
Not internally connected.
2
VGHM
Output of GPM circuit. This output directly drives the supply for the gate driver circuits.
3
VFLK
Determines when the TFT LCD is on or off. This is controlled by the timing controller in
the LCD module.
4
VDPM
VDPM pin is the enable signal for the GPM block. Pulling this pin high enables the GPM
while pulling this pin low disables it. VDPM is used for timing sequence control.
5
V
DD
Reference input for gate pulse modulation (GPM) circuit. The voltage at V
DD
is used to set
the lower VGHM voltage.
6
AV
IN
Op-Amp analog power input.
7
OUT
Output of the Op-Amp.
8
NEG
Negative input terminal of the Op-Amp.
9
POS
Positive input terminal of the Op-Amp.
10
AGND
Analog ground for the step-up regulator, LDO, and Op-Amp. Connect directly to DAP and
PGND beneath the device.
11
ADJ
LDO output voltage feedback input.
12
V
OUT
LDO regulator output.
LM331
1
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2
Pin Descriptions
(Continued)
Pin
Name
Function
13
LV
IN
LDO power input.
14
SS
Boost converter soft start pin.
15
V
C
Boost compensation network connection. Connected to the output of the voltage error
amplifier.
16
FREQ
Switching frequency select input. Connect this pin to V
IN
for 1.28MHz operation and
AGND for 660kHz operation.
17
V
IN
Boost converter and GPM power input.
18
SW
Boost power switch input. Switch connected between SW pin and PGND pin.
19
SHDN
Shutdown pin. Active low, pulling this pin low will disable the LM3311.
20
FB
Boost output voltage feedback input.
21
PGND
Power Ground. Source connection of the step-up regulator NMOS switch and ground for
the GPM circuit. Connect AGND and PGND directly to the DAP beneath the device.
22
CE
Connect capacitor from this pin to AGND.
23
RE
Connect a resistor between RE and PGND.
24
VGH
GPM power supply input. VGH range is 5V to 30V.
DAP
Die Attach Pad. Internally connected to GND. Connect AGND and PGND pins directly to
this pad beneath the device.
Block Diagrams
20126357
LM331
1
www.national.com
3
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