MIC79050 datasheet(10/28 Pages) MICROCHIP

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MIC79050

DS20005771B-page 10

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2017 - 2022 Microchip Technology Inc. and its subsidiaries.

4.0

FUNCTIONAL DESCRIPTION

The MIC79050 is a high-accuracy, linear battery

charging

circuit

designed

for

the

simplest

implementation of a single lithium-ion (Li-ion) battery

charger. The part can operate from a regulated or

unregulated power source, making it ideal for various

applications. The MIC79050 can take an unregulated

voltage source and provide an extremely accurate

termination voltage. The output voltage varies only

0.75% from nominal over the standard temperature

range for Li-ion battery charging (–5°C to +60°C). With

a minimum of external components, an accurate

constant-current charger can be designed to provide

constant-current, constant-voltage charging for Li-ion

cells.

4.1

Input Voltage

The MIC79050 can operate with an input voltage up to

16V (20V absolute maximum), ideal for applications

where the input voltage can float high, such as an

unregulated wall adapter that obeys a load-line. Higher

voltages can be sustained without any performance

degradation to the output voltage. The line regulation of

the device is typically 0.009%/V; that is, a 10V change

on the input voltage corresponds to a 0.09% change in

output voltage.

4.2

Enable

The MIC79050 has an enable pin that allows the

charger to be disabled when the battery is fully charged

and the current drawn by the battery has approached a

minimum and/or the maximum charging time has timed

out. When disabled, the regulator output sinks a

minimum of current with the battery voltage applied

directly onto the output. This current is typically 12 μA

or less.

4.3

Feedback

The feedback pin allows for external manipulation of

the control loop. This node is connected to an external

resistive divider network, which is connected to the

internal error amplifier. This amplifier compares the

voltage at the feedback pin to an internal voltage

reference. The loop then corrects for changes in load

current or input voltage by monitoring the output

voltage and linearly controlling the drive to the large,

PNP pass element. By externally controlling the

voltage at the feedback pin the output can be disabled

or forced to the input voltage. Pulling and holding the

feedback pin low forces the output low. Holding the

feedback pin high forces the pass element into

saturation, where the output will be the input minus the

saturation (dropout) voltage.

4.4

Battery Output

The BAT pin is the output of the MIC79050 and

connects directly to the cell to provide charging current

and voltage. When the input is left floating or grounded,

the BAT pin limits reverse current to <12 μA to minimize

battery drain.

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