Texas Instruments BQ25123, Manual, Page: 23 / 72

using the TMR 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.
In addition to the safety timer, the device contains a 50-second watchdog timer that monitors the host through
the I
2
C interface. Only after an I
2
C transaction is performed on the I
2
C interface, will the watchdog timer start.
In the case where the device is set to operate in High Impedance Mode, the watchdog timer is automatically
disabled and can only be re-started after the device exits the High Impedance Mode and a subsequent I
2
C
transaction is performed. The watchdog timer is reset by any transaction by the host using the I
2
C interface.
If the watchdog timer expires without a reset from the I
2
C interface, all registers except MRRESET_VIN and
MRREC are reset to the default values.
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 the Section 8.5 . 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 3.6 V).
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 Figure 9-4 . The resistor values
are calculated using Equation 1 and Equation 2 . 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
BATREG
– 140 mV
TS
BQ25123
RHI
RLO
1 x Charge/
0.5 x Charge
V
DRV
Figure 9-4. TS Circuit
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BQ25123
SLUSCZ6A – JANUARY 2018 – REVISED MAY 2021
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