CM9112 Datasheet, PDF (12/18 Pages) California Micro Devices Corp – Dual Inputs Dual Outputs High Accurate Fast Charger

PRELIMINARY
CM9112
Application Information (cont’d)
Q1 Gate
Drive
Vdc
Figure 4. Q1 Response to Undamped
Ringing at the Input
Charging status
CM9112 provides two charging status indicator pins:
STAT1 and STAT2. These are open-drain outputs,
which can drive LEDs directly, with up to 20mA of cur­
rent sinking capability. Alternatively, the system super­
visory microprocessor can monitor the battery charging
status by interfacing with these two pins, using a
100kΩ pull-up resistor for each pin. See Table 1.
CHARGE STATUS
Precharge in progress
Fast-charge in progress
Charge completed
Charge suspended
(including thermistor fault,
Precharge or Termination
timeout, OTP, OCP and
ENA pulled low)
STAT1
Low -
Low -
High -
STAT2
Low -
High -
Low -
High -
High -
Table 1: Charge Status for STAT1, STAT2
Thermistor Interface
Li-ion batteries are prone to overheating when exposed
to excess current or voltage. High heat, combined with
the volatile chemical properties of lithium, can cause
fire in some cases. The CM9112 provides a thermal
interface for over-temperature protection, allowing safe
charging of Li-ion cells.
For safety, manufacturers suggest suspending any
charging above 45°C and below 10°C until the battery
reaches the normal operating temperature range.
Charging below freezing must be avoided because
plating of lithium metal could occur. Battery capacity
will be reduced if charged between 0°C and +10°C due
to the inefficient charging process at low temperatures.
The CM9112 has incorporated a thermistor interface,
responsible for the temperature control of the battery-
pack through a negative temperature coefficient (NTC)
thermistor attached near the battery-pack. The inter­
face surveys the voltage on the THERM pin, which an
input to a window comparator with thresholds associ­
ated with two battery-pack fault conditions:
Vtherm<1/2 x V_IN for Battery Hot
Vtherm>7/8 x V_IN for Battery Cold
To avoid oscillation near the Vtherm thresholds, both
windows have an associated hysteresis of 200mV.
30K
20K
10K
0
COLD
Rc(28K)
Thermistor
Resistance
7/8*Vin
+
Vtherm
OK
Rh(4K)
1/2*Vin
HOT
0^oC
20^oC
40^oC
60^oC
Figure 5. Vtherm Windows
If the voltage on the THERM pin either exceeds 7/8 x
V_IN, or goes below 1/2 x V_IN, the CM9112 stops charg­
ing and STAT1, STAT2 signal a fault condition (both go
high). LDO1 remains fully functional and continues to
provide the necessarily current to VSYS (the Base­
band load). The charging resumes only when the volt­
age on the THERM pin returns to within the window of
1/2 x V_IN to 7/8 x V_IN. Figure 5 illustrates these win­
dows.
The thermistor interface consists of a thermistor con­
nected between THERM pin and ground, and a resis­
tor, Rtherm, connected between the THERM pin and
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07/06/06