RT9541
Preliminary
Applications Information
(1) Operation Description
Refering to the “Function Block Diagram”, when
charging voltage crosses the detector threshold from
a low value to a value higher than VDET1, the output
of COUT pin, the output of over-charge detector/VD1,
swiches to low level,..charger’s negative pin level.
After detecting over-charge the VD1 can be reset and
the output of COUT pin becomes “H” when the VDD
voltage is coming down to a level lower than “VDET1
– VHYS1”, or when a charger is disconnected from
the battery pack.
The short circuit protection function in charging
direction was also provided. When COUT high and
the “V-“ pin voltage 5V lower than VSS pin, the
RT9541 will turn low COUT with a fixed delay. The
COUT will go high after the short circuit condition
was removed.
After detecting over-discharge, supply current will be
kept extremely low by halting some internal circuits
operation. The output delay of over-charge detectors
can be set by connecting an external capacitor.
Output type of COUT and DOUT are CMOS.
The output of DOUT pin, the output of over-discharge
detector/VD2, switches to “L” after internally fixed
delay time passed, when discharging voltage crosses
the detector threshold from a high value to a value
lower than VDET2. An excess load current can be
sensed and cut off after internally fixed delay time
passsed through the built in excess current detector,
VD3, with DOUT being enabled to low level. Once
after detecting excess current, the VD3 is released
and DOUT level switches to “H” by detaching a
battery pack from a load system.
(2) Component Selection Guide:
Referring to “Typical Application Circuit”, R1 and
C1 will stabilize a supply voltage to the RT9541. A
recommended R1 value is less than 1kΩ. A larger
value of R1 leads higher detection voltage, makes
some errors, because of shoot through current
flowed in the RT9541.
R2 and C2 will stabilize a V- pin voltage. The
resetting from over-discharge with connecting
charger possibly be disabled by larger value of R2.
Recommended value is less than 1kΩ. And
recommended C2 value is less than 1µF.
Futher, short circuit protector makes DOUT level to
“L” immediately with external short circuit current and
removing external short circuit leads DOUT level to
“H”.
R1 and R2 can operate as a current limiter against
setting cell reverse direction or for applying excess
charging voltage to the RT9541. While smaller R1
and R2 may cause an over power dissipation rating
of the RT9541 and a total of “R1+R2” should be
more than 1kΩ.
The excess charging current is also monitored, and
the charging path will be cut off (by turn low COUT)
after excess charging current was detected lasting a
internally fixed delay time. The charging path will be
re-started (by turn high COUT) after another
internally fixed delay. If the excess charging current is
still there, the same process will be repeated and
cause the charging path toggling on and off with a
12.5% on duty. Such a protection function reduces
the average charging current to 12.5% of original
value when excess charging current detected.
www.richtek-ic.com.tw
DS9541-05 August 2001
4
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