Rainbow Electronics DS2770 - Manual (Page 8)

DS2770
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RECHARGEABLE LITHIUM PULSE CHARGING Figure 3
NiMH CHARGER OPERATION
During NiMH charging, charge current from a constant current or current-limited supply is gated to the
battery under control of UV and CC pins. Since the transition from trickle charge to fast charge occurs
when the battery reaches 3.0V, a three-cell NiMH battery will begin fast charge at 1.0V per cell. A
voltage divider can be used to adjust the transition point to a higher per cell voltage, though values in the
Voltage Measurement Register would be affected by the divider ratio.
At the start of fast charge, the DS2770 uses the most recent temperature measurement to determine the
appropriate dT/dt termination rate for the ambient conditions from Table 2 below. During the first 5
minutes, temperature rate termination is blanked to avoid false dT/dt detection due to I
2 R heating. After
the blanking period, dT/dt detection begins using one of the initial rates from Table 2 and requires that the
rate of temperature rise continue at or above the selected rate for 2.8 minutes. Internally, values from the
Temperature Measurement Register are averaged in determining the sustained rate of temperature rise.
The effective rate shown in Table 2 is based on NiMH charge data and represents the predicted
instantaneous dT/dt rate at termination.
NiMH CHARGE TERMINATION THRESHOLDS Table 2
dT/dt THRESHOLD AMBIENT
TEMPERATURE ( °C) INITIAL
( °C/MIN)
EFFECTIVE
( °C/MIN)
0 to +5 0.30 1.0
+5 to +15 0.45 1.0
+15 to +40 0.60 1.0
t
CD
Complete
Charge
Pulse Charge
Charge
Trickle
VIN
t
VCV
CC
UV
LB
CV
V
V
Pulse
Region
Bulk
Region