DC425B - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B
1MHZ SYNCHRONOUS BUCK-BOOST
LTC3440
DESCRIPTION
Demonstration Circuit 425B is a constant-frequency
synchronous Buck-Boost converter using the
LTC3440. The input range is from 2.5V to 5.5V, making it ideal for single-cell lithium-ion or three-cell
NiCd/NiMH battery applications. This converter provides up to 95% efficiency, much higher than traditional Buck-Boost converters. For 2.5V minimum input voltage, this converter can provide up to 500mA
load current.
The output voltage is set at 3.3V. A different output
voltage in the range of 2.5V to 5.5V can be obtained
by changing one of the feedback resistors. The fre-
quency is set at 1MHz, which is a good trade-off between efficiency and size. The frequency can be modified by changing R6 or by synchronizing to an external clock. In shutdown, the board draws about 2.5µA,
where 2µA goes through the 1MΩ pull up resistor
(R4) and the IC itself draws less than 1µA.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
QUICK START GUIDE
Refer to Figure 1 for the connection diagram and follow the procedure below:
1. Apply a voltage source to the input of the circuit
between the VIN and GND terminals. The circuit will
start up at input voltage higher than 2.5V.
NOTE
Do not apply more than 5.5V to the input.
2. Attach a voltmeter or oscilloscope probe between
the VOUT and GND terminals of the circuit to monitor
the output. To start the circuit, the shunt at JP1
needs to be put in RUN position.
3. Attach a load to the output. The available output
current depends on the input voltage.
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B
1MHZ SYNCHRONOUS BUCK-BOOST
PERFORMANCE SUMMARY
PARAMETER
CONDITION
VALUE
Input Voltage Range
2.5V to 5.5V
Maximum Load Current, Min
VOUT = 3.3V, VIN = 2.5V
500mA
Typical Output Ripple
VOUT = 3.3V, IOUT = 500mA
13mVP-P
Typical Operating Frequency
R6 = 62K
1MHz
TYPICAL PERFORMANCE CHARACTERISTICS
100
4.2V
EFFICIENCY (%)
90
3.6V
80
3.0V
70
2.7V
60
10
100
LOAD CURRENT (mA)
1000
Figure 2. Efficiency vs. Load Current (without External Schottky Diodes)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B
1MHZ SYNCHRONOUS BUCK-BOOST
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