SI9731 Datasheet, PDF (9/10 Pages) Vishay Siliconix – UP Controlled Battery Charger For 1-Cell Li-ion or 1-Cell to 3-Cell NiCd/NiMH Batteries

DETAIL OPERATIONAL DESCRIPTION
4.1 V_TAP
The Si9731’s internal feedback resistors are set to provide
4.2 V charge termination at V_BAT+ output if the 4.1 V_TAP is left
open circuit. Connecting the 4.1 V_TAP to V_BAT+ configures
Si9731 for 4.1 V charge termination at V_BAT+. This feature
allows Si9731 to accommodate Li-ion batteries requiring 4.1
V or 4.2 V charge termination. Caution: the 4.1 V_TAP should
not be connected to ground or any other voltage source as
this will cause the Si9731 to operate open loop and can result
in over charging the battery!
Feedback Disconnect Switch
The Si9731 includes a feedback disconnect switch (Q5 in
Figure 1) connected in series with the device’s internal feed-
back resistor string. The 42 kΩ feedback resistor string is
connected to ground when both the internal "OK to Charge"
signal and the CVMODE pin are at logic high, providing feed-
back voltage to Si9731’s error amplifier. This action helps
prevent the Si9731 from discharging the battery.
CHARGERPRESENT and CHARGERPOWERON
CHARGERPRESENT and CHARGERPOWERON are open
drain outputs, each requiring an external pull-up resistor.
CHARGERPRESENT pin goes low with CHARGERPRE-
SENTIN pin goes high, signaling the processor that a
charger has been inserted. CHARGERPOWERON Pin goes
low when CHARGERPOWERONIN Pin is high, charger volt-
age is not in UVLO and the battery voltage has increased to
above 3.4 V, turning on the system power supply since the
battery has been charged up to minimum operating voltage.
Input Over-Voltage Detector
The external dc source connected to the V_CHARGER pin
should be at 12 V or less. In the unlikely event that the volt-
age at V_CHARGER pin is at or above 12.8 V (typical), Si9731’s
internal over voltage detector will turn off MOSFETs Q1, Q2,
and Q5 and disable charging.
Si9731
Vishay Siliconix
Thermal Shutdown
Si9731 also includes a thermal protection circuit that sus-
pends charging through Q1 and Q2 when die temperature
exceeds 130 °C due to overheating. Once the die tempera-
ture cools to below 120 °C, the charging will resume.
Shutdown
Si9731 can be completely turned off by applying 0.4 V or less
to the device’s ON/OFF pin. In shutdown mode, Si9731
draws less than 1 µA quiescent current with charger voltage
below UVLO, and draws 500 µA when charger voltage is
above UVLO. The device is enabled by applying 1.5 V to
12 V at the ON/OFF pin. In applications where the device will
always remain enabled, the ON/OFF pin may be connected
to the V_CHARGER pin. Si9731’s shutdown circuitry includes
hysteresis, as such the device will operate properly even if a
slow moving signal is applied to the ON/OFF pin. When the
device is enabled, the battery voltage sense circuitry draws
approximately 25 µA from V_BAT.
OK to Charge (OTC)
Si9731 also includes an internal signal that enables both
trickle charge mode and fast charge mode operations, the
"OK to Charge" (or OTC) signal. The OTC signal is at logic
high if all of the following are satisfied:
1. Battery voltage is below 5 V
2. Charger voltage is greater than 2.6 V but below 12.8 V
3. V_CHARGER > V_BAT + 40 mV when MAINCHARGEEN =
Low
V_CHARGER > V_BAT - 40 mV when MAINCHARGEEN =
High
4. ON/OFF pin is at logic high.
In order to charge the battery in any manner, the OTC signal
has to be high.
Vishay Siliconix maintains worldwide manufacturing capability. Products may be manufactured at one of several qualified locations. Reliability data for Silicon Tech-
nology and Package Reliability represent a composite of all qualified locations. For related documents such as package/tape drawings, part marking, and reliability
data, see http://www.vishay.com/ppg?71321.
Document Number: 71321
S-60869-Rev. B, 22-May-06
www.vishay.com
9