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DS2770 Datasheet(PDF) 8 Page - Dallas Semiconductor |
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DS2770 Datasheet(HTML) 8 Page - Dallas Semiconductor |
8 / 27 page DS2770 8 of 27 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 I2R 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 |
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