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LTC4052-42

Lithium-Ion Battery Pulse Charger with Overcurrent Protection

Linear Integrated System 

LTC4052-4.2

APPLICATIO S I FOR ATIO

VIN

GATE

VOLTAGE

10µA/C

50µA/C

10µA/C

10µA/C

50µA/C

50µA/C

4052 TA02

Figure 2. Slew Rate at GATE and VIN Pins

with the RC Network from GATE to VIN

Thermal Considerations

The power handling capability is limited by the maximum

rated junction temperature (125°C) and the amount of PC

board copper used as a heat sink. The power dissipated by

the device consists of two components:

1. Input supply current multiplied by the input voltage

2. The voltage drop across the switch (SENSE pin to BAT

pin) multiplied by the charge current

The LTC4052 has internal thermal shutdown designed to

protect the IC from overtemperature conditions. For con-

tinuous charging in the fast charge mode, the maximum

junction temperature must not be exceeded. It is important

to give careful consideration to all sources of thermal

resistance from junction to ambient. Additional heat sources

mounted nearby must also be considered.

Surface mount packages rely primarily on the PC board

copper to dissipate the heat generated by the package to the

surrounding air. Since the PC board copper is the heat sink,

generous amounts of copper surrounding the package are

recommended to increase the effectiveness of the heat sink.

In addition, feedthrough vias or plated through holes (lo-

cated directly beneath the package and elsewhere) connect-

ing internal copper and backside copper layers help transfer

and spread the heat generated by the package.

Calculating Junction Temperature

Example: Find the maximum junction temperature for a

battery voltage of 4V (VIN will collapse to around VBAT in the

fast charge mode), charge current of 1A and a maximum

ambient temperature of 75°C.

The power dissipated by the IC is:

P = (IBAT • IBAT • RDS(ON)) + (VIN • IIN)

= (1A • 1A • 0.35Ω) + (4V • 1mA)

= 0.35 + 0.004

= 0.354W

The LTC4052 is available in an enhanced 8-pin MSOP

package which features an exposed copper pad on the

bottom of the package allowing it to be soldered directly to

the PC board copper for maximum heat transfer. This

greatly reduces the thermal resistance and increases the

power handling capability when compared to a standard

MSOP package. The junction to aimbient thermal resis-

tance of this package is approximately 35°C/W depending

on the copper area. The junction temperature rise above

ambient will be approximately:

(0.354W)(35°C/W) = 12.39°C

The maximum junction temperature will be equal to the

maximum junction temperature rise above ambient plus

the maximum ambient temperature or:

TJMAX = 85°C + 12.39°C = 97.39°C

ACPR Output Pin

When the input voltage is 45mV higher than the voltage at

the BAT pin, the ACPR pin is pulled to ground to indicate

that the input supply (wall adapter) is applied. After the

input supply is removed, this pin will become high imped-

ance. An internal 100ms filter prevents the LTC4052 from

turning off if the voltage at the VIN pin rings and gets too

close to VBAT due to parasitic inductance.

Stop Charging

The charger is off when the voltage at the VIN pin is less

than 45mV above VBAT (sleep mode). The charge pump

and the internal pass transistor are turned off, and the

internal resistor divider is disconnected to reduce the

current drain on the battery in the sleep mode.

405242i

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