QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 925
TRIPLE OUTPUT TFT LCD BIAS SUPPLY
1
LT3489EMS8E
DESCRIPTION
Demonstration circuit 925 features the LT3489EMS8E
in a circuit specifically designed to drive large
TFT/LCD displays. The demo circuit demonstrates
small size and low component count in a Boost Cir-
cuit. It converts a 3.3V-6V input to 8V at 600mA, 23V
at 10mA and -8V at 20mA. Since the maximum Vin of
the LT3489 is 16V, this Demo circuit will work well at
higher inputs. The only limitation is that the input has
to be lower than the Boost converter output (8V) in
order to stay in regulation.
This circuit is designed to demonstrate the capacitor
programmable Soft-Start feature, advantages of the
2MHz constant switching frequency and the internal
2.5A, 40V switch. This circuit is intended for large
TFT-LCD displays and other space-conscious applica-
tions such as Bias Supplies, GPS Receivers, DSL
Modems and Local Power Supplies.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (T
A
= 25°C)
PARAMETERS FOR 15V BOOST CIRCUIT CONDITION VALUE
Minimum Input Voltage 3.3V
Output Voltage V
OUT
V
IN
= 3.3V, I
OUT
= 0mA to 600mA 8V ±3%
Maximum Output Current for 8V Output Vin = 3.3V, 23V@10mA and -8V@20mA 600mA
Typical Output Ripple V
OUT
for 8V Output V
IN
= 3.3V , I
OUT
= 600mA 30mV
P–P
Typical Efficiency All Outputs Loaded V
IN
= 3.3V, Vout = 8V@400mA, -8V@20mA,
23V@10mA 83%
QUICK START PROCEDURE
Demonstration circuit 925 is easy to set up to evalu-
ate the performance of the LT3489EMS8E. 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 out-
put voltage ripple by touching the probe tip directly
across the Vin or Vout and GND terminals. See Figure
2 for proper scope probe technique.
1.
Place jumpers in the following positions:
On
2.
With power off, connect the input power supply to
Vin and GND.
3.
Turn on the power at the input.
4.
Check for the proper output voltages.
NOTE:
If there is no output, temporarily disconnect
the load to make sure that the load is not set too
high.
5.
Once the proper output voltages are established,
adjust the loads within the operating range and ob-
serve the output voltage regulation, ripple voltage,
efficiency and other parameters.
JP1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 925
TRIPLE OUTPUT TFT LCD BIAS SUPPLY
2
VIN
GND
Figure 1.
Proper Measurement Equipment Setup
Figure 2.
Measuring Input or Output Ripple
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 925
TRIPLE OUTPUT TFT LCD BIAS SUPPLY
3
