Linear LT1943 Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 620
HIGH CURRENT QUAD OUTPUT SWITCHING REGULATORS FOR TFT-LCD PANELS
DESCRIPTION
Demonstration circuit 620 is a quad output power
supply intended for use in large TFT-LCD panels. The
®
circuit features the LT 1943 high current quad-output
switching regulator and generates a 3.3V logic supply
along with the triple output supply required for the
TFT-LCD panels. With an input voltage range of 8V to
20V, a step down regulator provides 3.3V V
up to 2A current; a high power SEPIC converter, a
lower power boost converter and an inverting
converter provide three independent output voltages
AV , V and V required by the LCD panels. A high
DD ON OFF
side PNP provides delayed turn on of the V
and can source up to 30mA at 30V.
Table 1. Performance Summary (T
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage V
LOGIC
Maximum Output Current at V
Typical Output Ripple V
LOGIC
Typical Output Ripple AV
DD
Typical Switching Frequency
On/Off Control
Note 1: 2A maximum output current is guaranteed when V
rent at V . More output current is available at higher input voltage. Please refer to the LT1943 data sheet for output current vs. input voltage
LOGIC
curve.
QUICK START PROCEDURE
Demonstration circuit 620 is easy to set up to
evaluate the performance of the LT1943. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
LOGIC
ON
= 25°C unless otherwise noted)
A
CONDITION
-40°C to 85°C
-40°C to 85°C
V = 8V to 20V, I
IN
V = 8V to 20V (Note 1)
LOGIC IN
V = 12V, load at V
IN
V = 12V, load at AV
IN
Logic Low Voltage-Off, -40°C to 85°C
Logic High Voltage-On
is unloaded. Since V
OFF
All four switchers are synchronized to the internal
1.2MHz clock, allowing the use of low profile
inductors and ceramic capacitors. They all have soft-
start to limit start-up inrush current.
Long wires run from input sources (such as wall
adaptors) can cause large voltage spikes during initial
with
plug-in. C17 is installed on DC620 to damp the
possible voltage spikes.
applications when input source is close to the
regulator. Please refer to Application Note 88 for
details.
signal
Design files for this circuit board are available.
Call the LTC factory.
LT is a registered trademark of Linear Technology Corporation
= 0A to 2A
OUT
= 2A (20MHz BW)
LOGIC
= 500mA (20MHz BW)
DD
is supplied from V
OFF
When measuring the input or output
NOTE:
voltage ripple, care must be taken to avoid a long
ground lead on the oscilloscope probe. Measure
the input or output voltage ripple by touching the
LT1943
C17 is not required for
VALUE
8V
20V
3.3V ±3%
2A
23mV
P–P
64mV
P–P
1.2MHz
0.4V MAX
2.4V MIN
, the load at V reduces the available cur-
LOGIC OFF
1