CM9101 Datasheet, PDF (10/12 Pages) California Micro Devices Corp – Compact Cost-effective Fast Charger

PRELIMINARY
CM9101
Application Information (cont’d)
A thermistor with a room temperature value of about
10kΩ, or higher, will keep the interface current drain
from V_IN low. Choose the Rtherm value equal to R_hot,
with a 0.5% tolerance. A metal film resistor is best for
temperature stability.
For example, a typically used thermistor for this appli­
cation is Vishay Dale’s NTHS0603N02N1002J. This
thermistor has a R_hot (50°C) = 4kΩ and R_cold (0°C) =
28kΩ. The thermistor interface will work properly if
Rtherm is 4.02kΩ, .5%. At 25°C the thermistor value is
10kΩ. Therefore, a value of voltage at the THERM pin
will be:
Vtherm= ^10kΩ×5V =3.57V 25^oC
14kΩ
Vtherm= ^4kΩ×5V =2.5V 50^oC
8kΩ
Vtherm= ^28kΩ×5V =4.375V 0^oC
32kΩ
When using the CM9101 with a dummy battery, without
a thermistor attached, this function can be disabled by
connecting the THERM pin to GND. In this case, the
THERM interface will never provide a fault condition to
stop charge.
If there is no need for the thermistor interface, the
THERM pin could be used as a second ENABLE pin
for charging control. If the system has an additional
control condition for stop charge, then the THERM pin
could be used as a second control input. Connecting
the THERM pin to V_IN will stop charging, while pulling
to GND will resume charging.
Charging Control by the Host System
The CM9101 allows a host-system to take active con­
trol of the charging process by providing actual charg­
ing current monitoring via the 1000:1 current mirror on
R_ISET. This is especially useful for the system’s direct
control of the Termination threshold (preset to 5% of
CC mode level).
VIN
Thermistor
Interface
CM9101
Charger
Rtherm (4k)
THERM
NTC
VOUT _Battery
Pack
BSEN
Vishay
NTHS0603N02N1002 J
Figure 4. NTC Thermistor Interface
Because the thermistor is typically located on the bat­
tery-pack, removal of the battery-pack will remove the
thermistor, and cause value of voltage at the THERM
pin to go above the window and thus stop charging.
This allows the THERM interface to function also as a
battery present detector.
Mode Summary
Precharge mode is the typical charge starting mode
for pre-conditioning a deeply discharged battery
(<3.3V). A constant current of 10% of the programmed
Fast-charge current is applied to raise the voltage
safely above 3.3V.
Fast-charge mode is the constant current charging
mode that applies most of the battery charge. A pro­
grammed constant current is applied to bring the bat­
tery voltage to 4.2V.
Termination mode is the final charging mode, where a
constant voltage of 4.2V is applied to the battery until
the charge current drops below 5% or the programmed
Fast-charge current.
Standby mode is entered after a successful Termina­
tion mode and charging is done. Charging stops. In this
mode, the battery is monitored, and when its voltage
drops below the re-charge threshold, a new charge
cycle begins.
Shutdown mode is triggered by a charging fault.
These include THERM pin voltage outside the window
(battery is too hot, too cold, or removed), Input current
that exceeds 2.4A (OCP), the IC junction temperature
© 2006 California Micro Devices Corp. All rights reserved.
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06/30/06