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 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.
Three temperature thresholds are monitored: the cold battery threshold, the cool battery threshold, and the hot
battery threshold. These temperatures correspond to the V
(COLD)
, V
(COOL)
, 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.
The BQ25120F3A has the warm region disabled for applications that need charging to suspend beyond 45°C by
adjusting the Rhi and Rlo resistors. Refer to the setup guide tool
and equation below for calculating
the hot trip point.
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
BQ2512x
RHI
RLO
1 x Charge/
0.5 x Charge
V
DRV
Figure 9-4. TS Circuit
SLUSDI4A – OCTOBER 2018 – REVISED APRIL 2021
24
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