DC1137A - Demo Manual

DEMO CIRCUIT 1137
QUICK START LT3498
GUIDE
LT3498
20mA Six White LED Driver and OLED
driver with Integrated Schottky
WARNING!
DO NOT LOOK AT OPERATING LED.
This circuit produces light that can damage eyes.
DESCRIPTION
Demonstration circuit 1137 is a 20mA Six White
LED Driver and OLED driver with Integrated
Schottky featuring the LT3498. The LT3498 is a
dual output boost converter featuring a 2.3MHz
PWM LED driver and a PFM (Pulse Frequency
Modulation) OLED driver. The demo board is
designed to operate from 3V to 5V, ideal for LiIon battery powered dual display applications,
such as main and sub-displays for cell phones.
The LED driver runs at 2.3MHz fixed frequency,
results in tiny circuit size. It can drive 6 white
LEDs at 20mA from a minimum of 3V. The
demo board offers flexible LED dimming methods. Users can use DC dimming, filter PWM
dimming or direct PWM dimming. A MOSFET in
series with the LED string disconnects the output capacitor discharge path if PWM terminal
becomes low. This results in higher direct PWM
dimming ratio. The high side LED current sensing is versatile. The parts functions as a “onewire” current source from the LED string point of
view. The circuit protection clamps LED driver
output to 27V (typ) in open circuit condition.
When CTRL2 is higher than 1.5V, the demo
board OLED side output is 16V. It can deliver up
to 24mA from a 3V source. The OLED driver
features a novel PFM control technique. This
technique results in low output voltage ripple
and high efficiency over a wide load range. An
internal PMOS output disconnect switch turns
itself off in shutdown, disconnecting the output
from the input source. This disconnect function
is often required in OLED applications. This
switch also minimizes leakage current drain
from the battery.
The LT3498 datasheet gives complete description of the part, operation and application information. The datasheet must be read in conjunction with this quick start guide for working on or
modifying the demo circuit 1137.
Design files for this circuit board are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
1
LT3498
PERF ORM A NCE SU M M A RY
Specifications are at TA = 25°C
SYMBOL PARAMETER
VIN
Input Supply Range *
IOUT
Output Current
VOUT
Output Voltage
VOPEN
η
CAP1 pin Over voltage Protection
Efficiency
Fs
Switching Frequency
CONDITIONS
LED Driver
OLED Driver
LED Driver
OLED Driver
LED Driver, LED Open
LED Driver, VIN=3.6V
OLED Driver, VIN=3.6V, VOUT2=16V,
24mA
LED Driver
MIN
3
19
TYP
15.4
26
16
27
75
74
1.8
2.3
20
MAX
5
21
24
26
16.6
28
2.8
UNITS
V
mA
V
V
%
MHz
* The Input Supply Range of the demo circuit 1137 is limited by the input capacitor. The input voltage absolute maximum rating of the LT3498 is 12V.
Q U ICK STA RT PROCEDU RE
Demonstration circuit 1137 is easy to set up to
evaluate the performance of the LT3498. 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
probe tip directly across the input or output and GND terminals.
See Figure 2 for proper scope probe technique for VOUT2.
1. Place
jumper in the following positions to test
the LED driver circuit:
ON
JP1
2. Place jumper in the following positions to test
the OLED driver circuit:
ON
JP2
3. With power off, connect the input power supply to VIN and GND.
4. With
power off, connect the input power supply to PWM.
5. Turn
on the power at the input.
NOTE. Make sure that the input voltage does not exceed 5V.
6. Check
2
for the proper voltages and currents.
NOTE. If the LEDs do not light up, check all the jumper
settings.
7. Once
the proper operations are established,
adjust the input within the operating range
and observe the parameters interested.
8. For
the LED driver, to test filtered PWM dimming or direct DC dimming, remove jumper
JP1, apply a PWM or a DC signal to CTRL1
and observe the brightness of the LED output.
9. To
test direct PWM dimming, remove jumper
JP1, remove C4, short out R4, disconnect
PWM from VIN and reconnect PWM and
CTRL1 to the direct PWM source. Direct
PWM dimming is not applicable to the OLED
driver.
10. For
OLED driver, to alter VOUT2 by adjusting
CTRL2, remove jumper JP2, apply a voltage
between 0 and 1.5V to CTRL2 and observe
the VOUT2 voltage.
LT3498
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
3
LT3498
4
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