Datasheet DW01A (Fortune Semiconductor) - 9

DW01A 12. Design Guide
Selection of External Control MOSFET Suppressing the Ripple and Disturbance
from Charger
To suppress the ripple and disturbance from charger,
connecting R1 and C1 to VCC is recommended. FO
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y Because the overcurrent protection voltage is preset,
the threshold current for overcurrent detection is
determined by the turn-on resistance of the charge
and discharge control MOSFETs. The turn-on
resistance of the external control MOSFETs can be
determined by the equation: RON=VOIP/ (2 x IT) (IT
is the overcurrent threshold current). For example, if
the overcurrent threshold current IT is designed to
be 3A, the turn-on resistance of the external control
MOSFET must be 25mΩ. Be aware that turn-on
resistance of the MOSFET changes with
temperature variation due to heat dissipation. It
changes with the voltage between gate and source
as well. (Turn-on resistance of MOSFET increases
as the voltage between gate and source decreases). As the turn-on resistance of the external MOSFET
changes, the design of the overcurrent threshold
current changes accordingly. Rev. 1.1 Protection the CS pin R2 is used for latch-up protection when charger is
connected under overdischarge condition and
overstress protection at reverse connecting of a
charger. 9/14