CM9101 Datasheet, PDF (9/12 Pages) California Micro Devices Corp – Compact Cost-effective Fast Charger

PRELIMINARY
CM9101
Application Information (cont’d)
OTP and OCP
In addition to chip temperature regulation at 105°C, the
CM9101 provides absolute over-temperature shutdown
protection. In the case of a malfunctioning charger con­
trol, high ambient temperature or an unexpectedly high
IC thermal resistance, Rth_(JA) (for example; due to
faulty soldering of the charger IC chip). The CM9101
provides an absolute OTP shutdown at junction tem­
perature of 150°C.
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.
Charging status
CM9101 provides a charging status indicator pin: STAT.
This is an open-drain output, which can drive an LED
directly, with up to 20mA of current sinking capability.
Alternatively, the system supervisory microprocessor
can monitor the battery charging status by interfacing
with this pin, using a 100kΩ pull-up resistor. See Table
1.
CHARGE STATUS
Precharge in progress
Fast-charge in progress
Charge completed
Charge suspended (includ­
ing thermistor fault, OTP,
OCP and ENA pulled low)
STAT
Low ­
Low ­
High -
High -
Table 1: Charge Status for STAT
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 CM9101 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 CM9101 has incorporated a thermistor interface,
responsible for the temperature control of the battery-
pack through a negative temperature coefficient (NTC)
Rc(28K)
30K
Thermistor
20K
Resistance
10K
+
0
7/8*Vin
Vtherm
COLD
OK
Rh(4K)
1/2*Vin
HOT
0^oC
20^oC
40^oC
60^oC
Figure 3. 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 CM9101 stops charg­
ing. The charging resumes only when the voltage on
the THERM pin returns to within the window of 1/2 x
V_IN to 7/8 x V_IN. Figure 3 illustrates these windows.
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
V_IN, as shown in Figure 4. To determine the proper
value for Rtherm, the thermistor used in the battery-
pack should follow the 7:1 ratio on the Resistance vs.
Temperature curve (for example, Vishay Dale’s R-T
Curve 2):
-R----^C----^O----^L---^D---⁽---a----t--^φ·---0----^°---C-----⁾= 7
R_{H O T} ( a t φ 50 ° C )
© 2006 California Micro Devices Corp. All rights reserved.
06/30/06 490 N. McCarthy Blvd., Milpitas, CA 95035-5112 lTel: [phone] lFax: [phone] lwww.cmd.com
9