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bits. When the safety timer is active, changing the safety timer duration resets the safety timer. The device also
contains a 2X_TIMER bit that enables the 2X timer function to prevent premature safety timer expiration when
the charge current is reduced by a load on PMID, SYS, LS/LDO or a NTC condition. When t
2X_TIMER
function is
enabled, the timer is allowed to run at half speed when any loop is active other than CC or CV.
9.3.16 External NTC Monitoring (TS)
The I
2
C interface allows the user to easily implement the JEITA standard for systems where the battery pack
thermistor is monitored by the host. Additionally, the device provides a flexible voltage based TS input for
monitoring the battery pack NTC thermistor. The voltage at TS is monitored to determine that the battery is at a
safe temperature during charging.
To satisfy the JEITA requirements, four temperature thresholds are monitored: the cold battery threshold, the
cool battery threshold, the warm battery threshold, and the hot battery threshold. These temperatures
correspond to the V
(COLD)
, V
(COOL)
, V
(WARM)
, and V
(HOT)
threshold in
. Charging and timers are
suspended when V
(TS)
< V
(HOT)
or > V
(COLD)
. When V
(COOL)
< V
(TS)
< V
(COLD)
, the charging current is reduced to
half of the programmed charge current. When V
(HOT)
< V
(TS)
< V
(WARM)
, the battery regulation voltage is reduced
by 140 mV (minimum V
BATREG
under this condition is 3.6V).
The TS function is voltage based for maximum flexibility. Connect a resistor divider from V
IN
to GND with TS
connected to the center tap to set the threshold. The connections are shown in
. The resistor values
are calculated using
and
. To disable the TS function, pull TS above TS
OFF
threshold.
DISABLE
TEMP
PACK+
PACK–
+
+
+
+
V
DRV
TS COLD
TS HOT
TS WARM
TS COOL
V
– 140 mV
BATREG
TS
BQ25121A
RHI
RLO
1 x Charge/
0.5 x Charge
V
DRV
Figure 9-4. TS Circuit
IN
(COLD)
(HOT)
(COLD)
(HOT)
(LO)
IN
IN
(HOT)
(COLD)
(HOT)
(COLD)
1
1
V
x R
x R
x
V
V
R
=
V
V
R
x
1
R
x
1
V
V
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(1)
SLUSDA7A – APRIL 2018 – REVISED JANUARY 2021
24
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