SM6781BV Datasheet, PDF (7/10 Pages) Nippon Precision Circuits Inc – Ni-MH/Ni-Cd Battery Charger IC

SM6781BV
–∆V Detection Function
A –∆V condition is detected when the BATT voltage (V_BATT) falls 4mV (typ) or more below the peak battery
voltage, at which point the battery is deemed to be fully charged and quick charge finishes (valid for 1V <
V_BATT < 2V).
Vpeak
4mV
Quick charge time
− ∆V detect
Figure 3. Battery voltage change
–∆V Detection A/D Converter
The A/D converter employs double integration A/D conversion, and converts samples taken approximately
every 1.17 seconds.
–∆V Detection Timing
The –∆V detection and peak voltage detection are determined by the average value of 16 A/D converted sam-
ples. Consequently, –∆V detection timing occurs approximately every 18 seconds (16-sample length).
16
A/D convert
490ms max
1
2
3
1.17sec
15
16
Operation
Stop
− ∆V detect
Peak hold
and compare
Averaging
18.7sec
Peak hold
and compare
Figure 4. –∆V detection and A/D convert
Standby Mode
When the BATT input voltage exceeds the standby voltage V_STB, the device enters standby mode.
In this mode, the maximum charging time timer, –∆V detection prohibit timer, and peak voltage data are all
reset to zero. At this time, the CHGN and LEDN outputs both become high impedance.
Charge Inhibit (INH)
When INH goes HIGH, charge mode operation stops. While INH is HIGH, the internal timer stops, CHGN
goes LOW and LEDN outputs 1Hz pulse (LEDN flashes). When INH goes LOW, the SM6781BV is restored to
the previous state and the internal timer restarts. If INH is connected to temperature switch (NPC SM6611), it
realizes simple temperature control.
NIPPON PRECISION CIRCUITS—7