pt6112 China Resources Powtech (Shanghai) Co., Ltd, pt6112 Datasheet - Page 8

• Manufacturer Part Number: pt6112
• Description: Standalone Linear Li-ion Battery Charger With Thermal Regulation
• Manufacturer: China Resources Powtech (Shanghai) Co., Ltd

APPLICATION INFORMATION
Adjusting Charging Current
The charging current is programmed using 1%
precision resistor from PROG pin to ground. The
charging current and the programming resistor are
calculated using the following equations:
R
Charge status indicator
The charging status indicator pin has three different
states: strong pull down(about 10mA current sink),
weak pull down(about 6µA current sink), and high
impedance. The strong pull down mode indicates the
PT6112 is in a charging cycle. A weak pull down mode
indicates the Vcc reaches the UVLO and the charger is
ready to charge. The high impedance indicates the
PT6112 is in Under Voltage Lock Out (UVLO) mode:
either VCC is less than 100mV above the BAT pin
voltage or insufficient voltage is applied to the VCC
pin. A microprocessor can distinguish the three states.
Thermal limiting
An internal thermal feedback loop reduces the
programmed charge current if the die temperature
attempts to rise above a preset value of approximately
120℃. This feature protects the PT6112 from excessive
temperature and allows the user to push the limits of the
power handling capability of a given circuit board
China Resources Powtech (Shanghai) Limited
PT6112_DS Rev EN_1.0
PROG
=1000V/I
CHG
,
I
CHG
=1000V/R
600
500
400
300
200
100
0
PROG
Charge current VS battery voltage
VCC=5V Rprog=2K TA=25℃ SOT23-5
WWW.CRPOWTECH.COM
Battery voltage(V)
Charger with Thermal Regulation
Standalone Linear Li-Ion Battery
without risk of damaging the PT6112.
The conditions that cause the PT6112 to reduce charge
current through thermal feedback can be approximated
by considering the power dissipated in the IC. Nearly
all of this power dissipation is generated by the internal
MOSFET—this is calculated to be approximately:
PD = (V
Where PD is the power dissipated
The approximate ambient temperature at which the
thermal feedback begins to protect the IC is:
Reducing the voltage drop across the internal MOSFET
can significantly decrease the power dissipation in the
IC. This has the effect of increasing the current
delivered to the battery during thermal regulation. One
method is by dissipating some of the power through an
external component, such as a resistor or diode. By
dropping voltage across a resistor in series with a 5V
wall adapter, the on-chip power dissipation can be
decreased, thus increasing the thermally regulated
charge current.
T
T
A
A
= 120℃ – PD•θ
= 120℃ – (V
V
V
I
BAT
CC
CC
BAT
– V
is the input supply voltage
is the charge current.
is the battery voltage
BAT
) • I
CC
JA
BAT
– V
BAT
) • I
BAT
PT6112
•θ
JA
Page 8