LTC4069EDC-TRPBF View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC4069EDC-TRPBF

Standalone 750mA Li-Ion Battery Charger in 2 × 2 DFN with NTC Thermistor Input

Linear Technology 

LTC4069

Applications Information

with low impedance leads. Excessive lead length, however,

may add enough series inductance to require a bypass

capacitor of at least 1µF from BAT to GND. Furthermore,

a 4.7µF capacitor with a 0.2Ω to 1Ω series resistor from

BAT to GND is required to keep ripple voltage low when

the battery is disconnected.

High value capacitors with very low ESR (especially ceram-

ic) may reduce the constant-voltage loop phase margin.

Ceramic capacitors up to 22µF may be used in parallel

with a battery, but larger ceramics should be decoupled

with 0.2Ω to 1Ω of series resistance.

In constant-current mode, the PROG pin is in the feedback

loop, not the battery. Because of the additional pole created

by the PROG pin capacitance, capacitance on this pin must

be kept to a minimum. With no additional capacitance on

the PROG pin, the charger is stable with program resistor

values as high as 25k. However, additional capacitance on

this node reduces the maximum allowed program resis-

tor. The pole frequency at the PROG pin should be kept

above 100kHz. Therefore, if the PROG pin is loaded with

a capacitance, CPROG, the following equation should be

used to calculate the maximum resistance value for R­PROG:

RPROG

≤

2π

•

1

105 •

CPROG

Average, rather than instantaneous, battery current may be

of interest to the user. For example, if a switching power

supply operating in low current mode is connected in

parallel with the battery, the average current being pulled

out of the BAT pin is typically of more interest than the

instantaneous current pulses. In such a case, a simple RC

filter can be used on the PROG pin to measure the average

battery current as shown in Figure 5. A 10k resistor has

been added between the PROG pin and the filter capacitor

to ensure stability.

5V WALL

ADAPTER

750mA

ICHG

USB

POWER

500mA

ICHG

ICHG

BAT

D1 LTC4069

SYSTEM

LOAD

VCC

MP1

PROG

+ Li-Ion

BATTERY

MN1 4.02k

1k

2k

4069 F04

Figure 4. Combining Wall Adapter and USB Power

LTC4069

PROG

GND

10k

RPROG

CFILTER

CHARGE

CURRENT

MONITOR

CIRCUITRY

4069 F05

Figure 5. Isolating Capacitive Load on the PROG Pin and Filtering

Power Dissipation

The conditions that cause the LTC4069 to reduce charge

current through thermal feedback can be approximated

by considering the power dissipated in the IC. For high

charge currents, the LTC4069 power dissipation is ap-

proximately:

PD = (VCC – VBAT) • IBAT

where PD is the power dissipated, VCC is the input supply

voltage, VBAT is the battery voltage and IBAT is the charge

current. It is not necessary to perform any worst-case

power dissipation scenarios because the LTC4069 will

automatically reduce the charge current to maintain the

die temperature at approximately 115°C. However, the

For more information www.linear.com/LTC4069

4069fc

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