RN5VM1××C/D
OPERATION
• VD1/Over-Charge Detector
· The VD1 monitors VDD pin voltage. When the VDD voltage crosses over-charge detector threshold VDET1 from a low val-
ue to a value higher than the VDET1, the VD1 can sense over-charging and an external charge control Nch-MOS-FET
turns to “OFF” with COUT pin being at “L”.
· An output delay time for over-charge detection can be set by an external capacitor C3 connecting the Vss pin and Ct pin.
The external capacitor can make a delay time from a moment detecting over-charge to a time output a signal which
enables charge control Nch-MOS-FET for turning to “OFF”. Though the VDD voltage would be going up to a higher lev-
el than VDET1 if it is within a time period of the output delay time, VD1 would not output a signal for turning “OFF” of
charg control Nch-MOS-FET. The output delay time can be calculated as below:
(
)
C3 × VDD– 0.7
tVDET1 =
0.48 × 10–6
· A level shifter incorporated in a buffer driver for the COUT pin makes the “L” of COUT pin to the V- pin voltage and the “H”
of COUT pin is set to VDD voltage with CMOS buffer.
Reset conditions from overcharging of RN5VM1××C
· There can be two cases to reset the VD1 making the COUT pin level to “H” again after detecting over-charge. Resetting
the VD1 makes the charging system ready for resumption of charging process.
The first case is in such condition that a time when the VDD voltage is coming down to a level lower than “VDET1–VHYS1”.
While in the second case, disconnecting a charger from the battery pack can make the VD1 resetting when the VDD lev-
<
el is within hysteresis width (VDET1–VHYS1≤VDD VDET1)
· After detecting over-charge with the VDD voltage of higher than VDET1, connecting system load to the battery pack makes
load current allowable through parasitic diode of external charge control Nch-MOS-FET. The COUT level would be “H”
when the VDD level is coming down to a level below the VDET1 by continuous drawing of load current.
Reset conditions from overcharging of RN5VM1××D
· After detecting over-charge, the VD1 would not be released and COUT level would not switch to “H” again with the excep-
tion that a cell voltage reaches to a lower value than “VDET1–VHYS1” by self discharge of cell or else. After detecting over-
charge, when the VDD level stays at a value higher than “VDET1–VHYS1”, to connect battery pack to a system load makes
battery pack being disabled at for charging or discharging because of excess current detector operated being DOUT “L”.
11
RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
