TC3827 Datasheet, PDF (3/10 Pages) Microchip Technology – Lithium-Ion Battery Charger

Lithium-Ion Battery Charger
TC3827
PIN DESCRIPTION
Pin No.
8-Pin MSOP
1
2
3
4
5
6
7
8
Symbol
SHDN
GND
MODE
I_MON
V_OUT
V_DRV
V_SNS
V_IN
I/O DESCRIPTION
Type
Signal Input
Power
Signal Output
Voltage Output
Voltage Input
Signal Output
Signal Input
Power
Description
Shutdown Input
System Ground
Charge Mode Indicator
Buffered Copy of Current Sense Resistor Drop
Charger DC Output Voltage Sense
Gate Drive to External MOSFET
Current Sense Voltage Input
Charger DC Input Voltage
SHDN: When SHDN is low, V_DRV is pulled high to V_IN and the charge is interrupted.
GND: Connect to the battery’s negative terminal. See Layout Guidelines for information on system grounding.
V_OUT: 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. V_OUT pin draws typically 1µA from the battery when V_IN 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.
V_DRV: Gate drive output for the external PMOS pass device.
I_MON : 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.
V_IN: Charger power supply input (+6V absolute max.). Bypass to GND with a capacitor.
V_SNS: Battery charge current sense voltage feedback. This voltage is developed across a small value precision resistor
that is in series with the battery.
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 V_OUT
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 V_OUT pin. The
charging current follows the foldback characteristic as shown
in Figure 2. The sense resistor sets the maximum charging
current, I_MAX. The voltage drop across the current sense
resistor is sensed at the V_SNS input. An amplified copy of this
sense voltage is provided as output on the current monitor
pin (I_MON). 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 V_IN and V_OUT pins
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 (V_DRV pulled
up to V_IN 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.
© 2001 Microchip Technology Inc. DS21558A
3
TC3827-2 12/12/00