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LTC4007EGN Datasheet(PDF) 10 Page - Linear Technology |
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LTC4007EGN Datasheet(HTML) 10 Page - Linear Technology |
10 / 24 page 10 LTC4007 4007fa a low forward voltage drop from drain to source. If the voltage between DCIN and CLN drops to less than 25mV, the input FET is turned off slowly. If the voltage between DCIN and CLN is ever less than – 25mV, then the input FET is turned off in less than 10 µs to prevent significant reverse current from flowing in the input FET. In this condition, the ACP pin is driven low and the charger is disabled. Battery Charger Controller The LTC4007 charger controller uses a constant off-time, current mode step-down architecture. During normal op- eration, the top MOSFET is turned on each cycle when the oscillator sets the SR latch and turned off when the main current comparator ICMP resets the SR latch. While the top MOSFET is off, the bottom MOSFET is turned on until either the inductor current trips the current comparator IREV or the beginning of the next cycle. The oscillator uses the equation: t VV Vf OFF DCIN BAT DCIN OSC = – • to set the bottom MOSFET on time. The result is a nearly constant switching frequency over a wide input/output voltage range. This activity is diagrammed in Figure 1. TGATE OFF ON BGATE INDUCTOR CURRENT tOFF TRIP POINT SET BY ITH VOLTAGE ON OFF 4006 F01 Figure 1 OPERATIO Table 1. Truth Table For Indicator States TIMER MODE DCIN SHDN ACP** LOBAT FLAG** FAULT** ICL STATE CHG** Shut down by low adapter voltage <BAT LOW LOW LOW HIGH HIGH LOW Reset HIGH Charging a low bat >BAT LOW HIGH LOW HIGH* HIGH* HIGH* Running LOW Normal charging >BAT LOW HIGH HIGH HIGH HIGH* HIGH* Running LOW Input current limited charging >BAT LOW HIGH HIGH HIGH* HIGH* LOW Running LOW Charger paused due to thermistor out of range >BAT LOW HIGH X X LOW HIGH Paused LOW (from NTC) Shut down by SHDN pin X HIGH X X HIGH HIGH LOW Reset HIGH Terminated by low-battery fault (Note 1) >BAT LOW HIGH LOW HIGH* LOW LOW >T/4 HIGH (Faulted) Timer is reset when FLAG goes low, then >BAT LOW HIGH HIGH LOW HIGH LOW >T/4 HIGH terminates after 1/4 T after (Waiting FLAG = for Restart) LOW Terminated by expired timer >BAT LOW HIGH HIGH HIGH HIGH LOW >T HIGH (Waiting for Restart Timer defeated XXXXX XX X Forced LOW Shut down by undervoltage lockout >BAT LOW HIGH HIGH HIGH HIGH* LOW Reset HIGH* + <UVL *Most probable condition X = Don’t care, ** Open-drain output HIGH = OPEN with pull-up Note 1: If a depleted battery is inserted while the charger is in this state, the charger must be reset to initiate charging. |
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