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LT3652IDD-PBF

Power Tracking 2A Battery Charger for Solar Power

Linear Technology 

LT3652

APPLICATIONS INFORMATION

ripple current in the charger, so it must have an adequate

ripple current rating. RMS ripple current (ICVIN(RMS)) is:

ICVIN(RMS) ≅ ICHG(MAX) • (VBAT / VIN)•([VIN / VBAT] – 1)1/2,

BOOST Supply

The BOOST bootstrapped supply rail drives the internal

switch and facilitates saturation of the switch transistor.

Operating range of the BOOST pin is 0V to 8.5V, as refer-

where ICHG(MAX) is the maximum average charge current

(100mV/RSENSE). The above relation has a maximum at

VIN = 2 • VBAT, where:

ICVIN(RMS) = ICHG(MAX)/2.

The simple worst-case of ½ • ICHG(MAX) is commonly

used for design.

Bulk capacitance is a function of desired input ripple volt-

age (ΔVIN), and follows the relation:

SW

LT3652

BOOST

SENSE

BAT

3652 F01

RSENSE

Figure 1. Programming Maximum Charge

Current Using RSENSE

CIN(BULK) = ICHG(MAX) • (VBAT/VIN) / ΔVIN (μF)

Input ripple voltages above 0.1V are not recommended.

10μF is typically adequate for most charger applica-

tions.

Charge Current Programming

The LT3652 charger is configurable to charge at average

currents as high as 2A. Maximum charge current is set by

choosing an inductor sense resistor (RSENSE) such that

the desired maximum average current through that sense

resistor creates a 100mV drop, or:

enced to the SW pin. Connect a 1μF or greater capacitor

from the BOOST pin to the SW pin.

The voltage on the decoupling capacitor is refreshed

through a diode, with the anode connected to either the

battery output voltage or an external source, and the

cathode connected to the BOOST pin. Rate the diode

average current greater than 0.1A, and reverse voltage

greater than VIN(MAX).

To refresh the decoupling capacitor with a rectifying diode

from the battery with battery float voltages higher than

8.4V, a >100mA Zener diode can be put in series with

the rectifying diode to prevent exceeding the BOOST pin

operating voltage range.

RSENSE = 0.1 / ICHG(MAX)

where ICHG(MAX) is the maximum average charge current.

A 2A charger, for example, would use a 0.05Ω sense

resistor.

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