Preliminary
Constant Voltage Regulation and Charge
Termination Mode
When the battery voltage reaches the regulation voltage
V
O(REG)
, the constant voltage feedback control starts, and
then the charge current begins to decrease as the typical
charge profile shown. As the charge current decreases
to lower than charge terminated current threshold, the
RT9501 will terminate the charge cycle.
Recharge Mode
After the charge termination mode, if the battery voltage
falls to lower than the recharge threshold voltage V
O(RCH)
,
the RT9501 will begin a new charge cycle according to
the battery voltage.
Battery Temperature Detection
The RT9501 continuously detects the battery temperature
by measuring the TS pin voltage. A NTC or PTC
thermistor can parallel with R
T2
to deviate the TS pin
voltage. (As shown in Figure 5) The TS pin voltage must
be within normal temperature voltage range that is shown
in Figure 6 and electrical characteristics, and then RT9501
can start working normally.
The R
T1
and R
T2
can be derived from following equations.
For NTC Thermistors:
R
T1
FB/CE
CS
VDD
R
T2
STAT
CC
BATT
TS
GND
V
IN
R
CS
R4
Q1
RT9501A/B
Battery
Pack
+
C2
Thermistor
Figure 5
VDD
Temperature Fault Range
V
TS2
Normal Temperature Range
V
TS1
Temperature Fault Range
GND
Figure 6
FB/CE Pin Functions
This pin has two functions, one is to enable/disable the
charge function, and the other is to finely adjust battery
regulation voltage. Connect this pin to VDD to enable
RT9501, and connect to ground to disable it (Figure 7). If
this pin is connected to a voltage divider as shown in
Figure 8, it can be a 2.1V reference voltage to adjust the
output regulation voltage as desired.
R
CS
R4
R
CE
CE
GPIO
CS
VDD
STAT
CC
BATT
TS
GND
R
T1
=
R
T2
=
5
×
R
TH
×
R
TL
3
×
(R
TL
- R
TH
)
5
×
R
TH
×
R
TL
[(2
×
R
TL
) - (7
×
R
TH
)]
V
IN
Q1
Battery
For PTC Thermistors:
R
T1
=
R
T2
=
5
×
R
TH
×
R
TL
3(R
TH
- R
TL
)
5
×
R
TH
×
R
TL
[(2
×
R
TH
) - (7
×
R
TL
)]
Where R
TL
is the resistance value in lowest desired
operation temperature and R
TH
is the resistance value in
highest desired operation temperature. The resistances
of thermistors are specified by the thermistor
manufacturer. If the temperature monitoring function is
not desired, there's an easy method to set R
T1
and R
T2
at
the same value and disconnect the thermistor to disable
this function.
Figure 7. For CE pin Function
DS9501A/B-07 March 2007
www.richtek.com
7
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
