Linear Technology LTC3440 User 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, 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:

Apply a voltage source to the input of the circuit

between the V

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.

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.

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

PERFORMANCE SUMMARY

PARAMETER CONDITION VALUE

Input Voltage Range 2.5V to 5.5V

Maximum Load Current, Min V

OUT

= 3.3V, V

= 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

EFFICIENCY (%)



LOAD CURRENT (mA)

100

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

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