Linear Technology LTC3440 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B
1MHZ SYNCHRONOUS BUCK-BOOST
1
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, mak-
ing it ideal for single-cell lithium-ion or three-cell
NiCd/NiMH battery applications. This converter pro-
vides up to 95% efficiency, much higher than tradi-
tional Buck-Boost converters. For 2.5V minimum in-
put 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 be-
tween efficiency and size. The frequency can be modi-
fied by changing R6 or by synchronizing to an exter-
nal clock. In shutdown, the board draws about 2.5µA,
where 2µA goes through the 1MΩpull 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 fol-
low the procedure below:
1. Apply a voltage source to the input of the circuit
between the V
IN
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 V
OUT
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

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B
1MHZ SYNCHRONOUS BUCK-BOOST
2
PERFORMANCE SUMMARY
PARAMETER CONDITION VALUE
Input Voltage Range 2.5V to 5.5V
Maximum Load Current, Min V
OUT
= 3.3V, V
IN
= 2.5V 500mA
Typical Output Ripple V
OUT
= 3.3V, I
OUT
= 500mA 13mV
P-P
Typical Operating Frequency R6 = 62K 1MHz
TYPICAL PERFORMANCE CHARACTERISTICS
100010
100
60
EFFICIENCY (%)

LOAD CURRENT (mA)
100
80
70
90
4.2V
3.6V
3.0V
2.7V


Figure 2. Efficiency vs. Load Current (without External Schottky Diodes)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B
1MHZ SYNCHRONOUS BUCK-BOOST
3