DC1089B - Demo Manual

DEMO CIRCUIT 1089
LT3502A
QUICK START
GUIDE
LT3502A
2.2MHz, 500mA, Step-down Regulator in
2mm × 2mm DFN
DESCRIPTION
Demonstration circuit 1089 is a monolithic step-down
DC/DC switching regulator featuring the LT3502A. The
demo circuit is designed for 5V output from a 7V to 40V
input. The wide input range of the LT3502A allows a variety of input sources including automotive batteries and
24V industrial supplies. The high switching frequency
allows the use of tiny, low cost external components.
Constant switching frequency above the AM band avoids
interfering with radio reception. The current mode control scheme creates fast transient response and good
loop stability. The boost diode is internal to reduce
component count. The SHDN pin can also be used to
program soft start. In this mode, the SHDN pin is driven
through an external RC filter to create a voltage ramp on
this pin. The soft start function reduces the input current
surge during start-up. Cycle by cycle current limit and
frequency foldback provide the protection against
shorted outputs. DA pin can further protect the silicon
under fault conditions by sensing the diode current.
The LT3502A 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 1089.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Performance Summary (TA = 25oC)
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage VOUT
Switching Frequency
Maximum Output Current
Efficiency
Voltage Ripple
CONDITION
VIN = 12V, IOUT = 500mA
VIN = 12V, IOUT = 500mA
VALUE
7V
40V
4.98V ±3%
2.25MHz
500mA
84%
10mV
QUICK START PROCEDURE
Demonstration circuit 1089 is easy to set up to evaluate
the performance of the LT3502A. 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
VIN or VOUT and GND terminals. See Figure 2 for proper scope probe
technique.
1. Place JP1 on the ON position.
2. With power off, connect the input power supply to
Vin and GND.
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 40V.
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 voltage is established, adjust
the load within the operating range and observe the
1
LT3502A
output voltage regulation, ripple voltage, efficiency
and other parameters.
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
2
LT3502A
TRANSIENT RESPONSE
The demo board 1089 is optimized for size. A feedforward capacitor is used to ensure the good transient
performance. Figure 3 shows the transient response of
the demo board. The input voltage is 12V. The output
voltage is 5V and the load current is stepped from
150mA to 400mA.
IL
200mA/DIV
Vout
100mV/DIV
AC coupled
10μs/DIV
Figure 3. Transient Response
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LT3502A
4
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