DC1293A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1293A
MONOLITHIC STEP-DOWN SWITCHING REGULATOR WITH LDO
LT1939
Demo circuit 1293A is a monolithic step-down switching regulator with LDO featuring LT1939. The demo
circuit is designed for 5.0V and 3.3V outputs from a 7V
to 25V input. The LDO output is configured as a postregulator of the switching regulator output. The total
current capability is up to 2A.
The switching regulator can be synchronized to an external clock input or be resistor-programmed to a
250kHz to 2.2MHz internal oscillator. Programmable
frequency allows for optimization between efficiency
and external component size. Cycle-by-cycle current
limit, frequency foldback and thermal shutdown provide
protections against a shorted output. The soft-start feature controls the ramp rate of the output voltage, elimi-
Performance Summary ( TA = 25oC )
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage VOUT1
Output Voltage VOUT2
Switching Frequency
Maximum Total Output Current (I OUT1 +I OUT2)
Voltage Ripple VOUT1
Voltage Ripple VOUT2
nates input current surge during startup, and also provides output tracking.
The LT1939’s low current shutdown mode (<12uA)
enables easy power management in battery-powered
systems.
The LT1939 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 1293A.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
CONDITION
VIN=12V, IOUT1=1.5A
VIN=12V, IOUT2=0.5A
VALUE
7V
25V
5.0V ±4%
3.3V ±4%
800kHz
2.0A
10mV
5mV
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1293A
MONOLITHIC STEP-DOWN SWITCHING REGULATOR WITH LDO
Demo circuit 1293A is easy to set up to evaluate the
performance of the LT1939. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 25V.
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.
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
VIN or VOUT and GND terminals. See Figure 2 for proper scope probe
technique.
5. Once
the proper output voltages are established, adjust the load within the operating range and observe
the output voltage regulation, ripple voltage, efficiency and other parameters.
1. Place JP1 on the RUN position.
2. With
power off, connect the input power supply to
VIN and GND.
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1293A
MONOLITHIC STEP-DOWN SWITCHING REGULATOR WITH LDO
Install a 20K resistor at R16 to enable SYNC function.
Install both R1 and R3 for the UVLO function, otherwise, let SHDN pin float for normal operation. See datasheet
“Shutdown and Undervoltage Lockout” for resistor calculation.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1293A
MONOLITHIC STEP-DOWN SWITCHING REGULATOR WITH LDO
4
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