NCP1850
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level or 400mA. The initial charge current will be
re−established when the die temperature falls below the
TWARN again.
If bit TJ_WARN_OPT = 0 (register CTRL1), the charge
current is not automatically reduced, no current changes
actions are taken by the chip until TSD.
Battery Temperature Management
For battery safety, charging is not allowed for too cold or
too hot batteries. The battery temperature is monitored
through a negative temperature coefficient (NTC)
thermistor mounted in the battery pack or on the phone PCB
close to the battery pack. In some cases the NTC is handled
by the platform and will not be connected to the charger IC.
NCP1850 provides a NTC pin for monitoring an external
NTC thermistor. NTC pin is connected to an internal voltage
VREG through pull−up resistor (RNTCPU). By connecting a
NTC thermistor between NTC pin and GND, internal
comparators can monitors voltage variation and provides
temperature information to the state machine.
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NTC
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NCP1850
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Figure 9. NTC Monitoring Circuit
RNTCPU
VREG
VRMOVED
VCOLD
VCHILLY
VWARM
VHOT
VNTCDIS
Two thresholds ‘cold’ and ‘hot’ are provided those are
programmable. The corresponding voltage levels of these
thresholds are respectively VCOLD and VHOT. Interrupts
(describe in section Charge status reporting) are generated
when crossing either threshold. The charge is halted outside
the cold−hot window. In addition to the above, comparators
monitor the NTC presence. When the NTC is removed
(VNTC > VNTCRMV) , no more charge current is supplied to
the battery and an interrupt is generated (describe in section
Charge status reporting). This functionality can be disabled
through programming (bit NTC_EN in register CTRL1).
When the NTC is not used in the application the NTC pin can
be tied to ground (VNTC < VNTCDIS) which will disable the
battery temperature monitoring function.
Regulated Power Supply (Trans pin)
NCP1850 has embedded a linear voltage regulator
(VTRANS) able to supply up to ITRMAX to external loads.
This output can be used to power USB transceiver. Trans pin
is enabled if a VBUS valid is connected on input pin
(VBUSUV < VIN < VBUSOV) and can be disabled through I2C
(bit TRANS_EN_REG register CTRL2). A current limiter
protects the IC in case of short circuit on TRANS pin.
Charge Status Reporting
Charge Status on FLAG Pin
FLAG pin is used to report charge status to the system
processor and also for interruption request.
During charger active states and wait state, the pin FLAG
is low in order to indicate that the charge of the battery is in
progress. When charge is completed or disabled or a fault
occurs, the FLAG pin is high as the charge is halted.
Interruption on FLAG pin
Upon any state or status change, the system controller can
be informed by sensing FLAG pin. A TFLAGON pulse is
generated on this pin in order to signalize all events listed in
the STAT_INT, CH1_INT, CH2_INT, BST_INT registers.
All these bits are read to clear. The register map indicated the
active transition of each bits (column “TYPE” Register Map
section).
If more than 1 interrupt appears, only 1 pulse is generated
while interrupt registers (STAT_INT, CH1_INT, CH2_INT,
BST_INT) will not fully clear.
The level of this pulse depends on the state of the charger
(see Charging process section):
−When charger in is charger active states and wait state
the FLAG is low and consequently the pulse level on
FLAG pin is high.
−In the others states, the pulse level is low as the FLAG
stable level is high.
This Pulse can be globally masked due to the
INT_FLG_MASK bit (Register CTRL1).
Interruption on INTB Pin
Upon any state or status change, the system controller can
be informed by sensing INTB pin. This pin is tied low in
order to signalize all events listed in the STAT_INT,
CH1_INT, CH2_INT, BST_INT registers and can be
individually masked with the corresponding mask bits in
registers STAT_MSK, CH1_MSK, CH2_MSK and
BST_MSK. All interrupt signals on INTB pin can be
masked with the global interrupt mask bit (bit INT_MASK
register CTRL1). All these bits are read to clear. The register
indicated the active transition of each bits (column “TYPE”
Register Map section).