DC1121A - Demo Manual

DEMO C IR C U IT 1 1 2 1
Q U IC K S TA R LTC3524
T G U IDE
L T C 3 5 2 4 EU F
A d ju s ta b le T F T B ia s S u p p ly w ith W L ED Driv e r
DESCRIPTION
Demonstration circuit 1121 is a bias and white LED
power converter solution for small/medium-sized TFTLCD panels. The circuit features the LT3524 adjustable
TFT bias supply with white LED driver. The LTC3524 can
operate from a single Lithium-Ion/polymer battery or any
voltage source between 2.5V and 6V, making it ideal solution for PDAs, GPS and handheld portable displays. A
synchronous boost convert provides 5V with up to
25mA. Regulated, low ripple charge pump regulators
provides 12.5V and -7.5V at 2mA. The output sequencing is internally controlled to insure proper initialization
and rapid discharge of the LCD panel in shutdown. An-
other 1.5M Hz boost converter powers two LED strings
with 4 series elements each.
The LTC3524 datasheet gives a complete description of
the part,operation and application information. The datasheet must be read in conjunction with this quick start
guide for Demo circuit 1121.
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation. ThinSOT and
PowerPath are trademarks ofLinear Technology Corporation.
Perform ance Sum m ary ( TA = 25oC )
PAR AM ETER
M inimum Input Voltage
M aximum Input Voltage
O utput Voltage V OUT
M aximum O utput Current at V OUT
Current at LED1 or LED2
Typical Switching Frequency
CO N DITIO N
R10=100kΩ
VALU E
2.5V
4.6V
5V +/- 5%
25mA
20mA +/- 10%
1.5M H z
Q U ICK STA RT PROCEDU RE
Demonstration circuit 1121 is easy to set up to evaluate
the performance of the LTC3524. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
NOTE. W hen measuring the input or output voltage ripple,care must be
taken to avoid a long ground lead on the oscilloscope probe. M easure the
input or output 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 JP1,JP2 and JP3 on the O N position.
2. W ith power off,connect the input power supply to Vin
and GND.
3. Turn on the power at the input. Observe all white LEDs
light up. W arning! Do not look directly at lighting LED.
This circuit produces light that can damage eyes.
4. Check for the proper output voltage.
NOTE. Ifthere is no output,temporarily disconnect the load to make sure
that the load is not set too high.
5. Once the proper output voltage is established, adjust
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency
and other parameters.
1
LTC3524
_
V
_
_
A
+
_
+ A +
_
+
+_
Figure 1. Proper M easurem ent Equipm ent Setup
GND
VIN
Figure 2. M easuring Input or Output R ipple
2
V
_
+
Load
V
+
+
A
+
_ A +_
Load
+
V
Load
+
_
_
_
LTC3524
3
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