Linear LT1943 Quick Start Manual
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 620
HIGH CURRENT QUAD OUTPUT SWITCHING REGULATORS FOR TFT-LCD PANELS
LT1943
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 VLOGIC with
up to 2A current; a high power SEPIC converter, a
lower power boost converter and an inverting
converter provide three independent output voltages
AVDD, VON and VOFF required by the LCD panels. A high
All four switchers are synchronized to the internal
1.2MHz clock, allowing the use of low profile
inductors and ceramic capacitors. They all have softstart to limit start-up inrush current.
Long wires run from input sources (such as wall
adaptors) can cause large voltage spikes during initial
plug-in. C17 is installed on DC620 to damp the
possible voltage spikes. C17 is not required for
applications when input source is close to the
regulator. Please refer to Application Note 88 for
details.
side PNP provides delayed turn on of the VON signal
and can source up to 30mA at 30V.
Design files for this circuit board are available.
Call the LTC factory.
LT is a registered trademark of Linear Technology Corporation
Table 1. Performance Summary (T
PARAMETER CONDITION VALUE
Minimum Input Voltage -40°C to 85°C 8V
Maximum Input Voltage -40°C to 85°C 20V
= 25°C unless otherwise noted)
A
Output Voltage V
Maximum Output Current at V
Typical Output Ripple V
Typical Output Ripple AVDD V
Typical Switching Frequency 1.2MHz
On/Off Control
Note 1: 2A maximum output current is guaranteed when V
rent at V
curve.
. More output current is available at higher input voltage. Please refer to the LT1943 data sheet for output current vs. input voltage
LOGIC
V
LOGIC
V
LOGIC
V
LOGIC
= 8V to 20V, I
IN
= 8V to 20V (Note 1) 2A
IN
= 12V, load at V
IN
= 12V, load at AVDD = 500mA (20MHz BW) 64mV
IN
Logic Low Voltage-Off, -40°C to 85°C 0.4V MAX
Logic High Voltage-On 2.4V MIN
is unloaded. Since V
OFF
= 0A to 2A 3.3V ±3%
OUT
= 2A (20MHz BW) 23mV
LOGIC
is supplied from V
OFF
, the load at V
LOGIC
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:
NOTE: When measuring the input or output
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
P–P
P–P
reduces the available cur-
OFF
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 620
HIGH CURRENT QUAD OUTPUT SWITCHING REGULATORS FOR TFT-LCD PANELS
probe tip directly across the VIN or V
OUT
GND terminals. See Figure 2 for proper scope
probe technique.
1.
Make sure the input voltage does not exceed 20V.
With power off, connect the input power supply to
VIN and GND.
2.
Turn on the power at the input.
and
3.
Check for the proper output voltages. If there is no
output, temporarily disconnect the load to make
sure that the load is not set too high.
4.
Once the proper output voltages are established,
adjust the loads within the operating range and observe the output voltage regulation, ripple voltage,
efficiency and other parameters.
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
VIN
GND
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 620
HIGH CURRENT QUAD OUTPUT SWITCHING REGULATORS FOR TFT-LCD PANELS
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