TC3827 datasheet(3/10 Pages) MICROCHIP

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Lithium-Ion Battery Charger

TC3827

TC3827-2 12/12/00

DS21558A

Pin No.

8-Pin MSOP

Symbol

Type

Description

SHDN

Signal Input

Shutdown Input

GND

Power

System Ground

MODE

Signal Output

Charge Mode Indicator

4IMON

Voltage Output

Buffered Copy of Current Sense Resistor Drop

5VOUT

Voltage Input

Charger DC Output Voltage Sense

6VDRV

Signal Output

Gate Drive to External MOSFET

7VSNS

Signal Input

Current Sense Voltage Input

8VIN

Power

Charger DC Input Voltage

PIN DESCRIPTION

FUNCTIONAL DESCRIPTION

The TC3827 controller only requires a P-channel power

MOSFET and two small capacitors to perform as an inex-

pensive Li-Ion battery charger. The TC3827 controller drives

an external PMOS to provide a regulated output current to

charge the battery. Initially, current limited charging occurs

until a pre-specified battery voltage is measured at the VOUT

pin. It then switches to constant-voltage mode. During

constant-voltage mode the TC3827 works like a linear

regulator, holding the output voltage within the specified

accuracy. The charger output is sensed at the VOUT pin. The

charging current follows the foldback characteristic as shown

in Figure 2. The sense resistor sets the maximum charging

current, IMAX. The voltage drop across the current sense

resistor is sensed at the VSNS input. An amplified copy of this

sense voltage is provided as output on the current monitor

pin (IMON). When the battery is deeply discharged to a

minimum voltage level, or if the battery is shorted, the

current sense circuit folds back the charge current to limit the

power dissipation of the PMOS. Both the VIN and VOUT pins

I/O DESCRIPTION

SHDN: When SHDN is low, VDRV is pulled high to VIN and the charge is interrupted.

GND:

Connect to the battery’s negative terminal. See Layout Guidelines for information on system grounding.

VOUT:

Battery positive terminal and charger regulated output voltage.This pin is connected to the external PMOS drain

and directly to the load for optimal regulation. VOUT pin draws typically 1µA from the battery when VIN power

is removed. Requires a Bypass capacitor.

MODE: Charge Status Indicator. Mode is an open-drain, N-channel MOSFET capable of sinking

20mA for an LED status indication of charger in current limited mode. LED is off in current-voltage mode.

VDRV:

Gate drive output for the external PMOS pass device.

IMON :

Battery Charge current profile. This output is an amplified copy of the voltage drop across the current sense resistor.

It can be used as input to an A/D converter to provide the controller with information about the charge current

profile.

VIN:

Charger power supply input (+6V absolute max.). Bypass to GND with a capacitor.

VSNS:

Battery charge current sense voltage feedback. This voltage is developed across a small value precision resistor

that is in series with the battery.

of the IC need a suitable bypass capacitor. The TC3827 also

has a logic-level shutdown input, SHDN, which may be

connected to the input voltage to enable the IC. Pulling it

“low” or to ground will disable the PMOS drive (VDRV pulled

up to VIN voltage). Also, a charger mode pin (MODE) is

provided to drive an optional LED for a visual indication of

current limited mode operation. LED will be turned off in

constant voltage mode operation.

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