fs312f-p Fortune Semiconductor Corporation, fs312f-p Datasheet - Page 9

• Manufacturer Part Number: fs312f-p
• Description: One Cell Lithium-ion/polymer Battery Protection Ic
• Manufacturer: Fortune Semiconductor Corporation

FS312F-P
12. Design Guide
12.1 Selection of External Control MOSFET
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.
12.2 Suppressing the Ripple and Disturbance from Charger
To suppress the ripple and disturbance from charger, connecting R1 and C1 to VCC is recommended.
12.3 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.
Rev. 2.2
9/14