EUP8051A
For PTC Thermistors
5 × R
× R
TH
TH
TC
TC
R
R
=
=
---------------------- (5)
T1
3× (R
- R
)
5 × R
× R
TH
TC
------------- (6)
T2
[(2 × (R
) - (7 × R
)]
TH
TC
Where R(TC) is the cold temperature resistance and R(TH)
is the hot temperature resistance of thermistor, as
specified by the thermistor manufacturer.
RT1 or RT2 can be omitted if only one temperature (hot or
cold) setting is required. Applying a voltage between the
V(TS1) and V(TS2) thresholds to pin TS disables the
temperature-sensing feature.
R
R
FB1
FB2
V
= 2.15 × (1 +
)V
O(REG)
Charge Termination andRecharge
The EUP8051A monitors the charging current during the
voltage-regulation phase. The EUP8051A declares a done
condition and terminates charge when the current drops
to the charge termination threshold, I(TERM). A new charge
cycle begins when the battery voltage falls below the
V(RCH) threshold.
Battery TemperatureMonitoring
The EUP8051A continuously monitors temperature by
measuring the voltage between the TS and VSS pins. A
negative-or a positive-temperature coefficient thermistor
(NTC, PTC) and an external voltage divider typically
develop this voltage (See Figure9). The EUP8051A
compares this voltage against its internal V(TS1) and V(TS2)
thresholds to determine if charging is allowed. (See
Figure10). The temperature sensing circuit is immune to
any fluctuation in VCC, since both the external voltage
divider and the internal thresholds (V(TS1) and V(TS2)) are
referenced to VCC.
The resistor values of R(T1) and R(T2) are calculated by the
following equations:
For NTC Thermistors
5 × R
× R
TH
TC
TC
TH
R
R
=
----------------------- (3)
T1
3× (R
- R
)
5 × R
× R
TH
TC
=
--------------- (4)
)]
T2
[(2 × (R
) - (7 × R
TH
TC
DS8051A Ver 1.1 Nov. 2006
12
EUTECH [ EUTECH MICROELECTRONICS INC ]
