Datasheet LTC4007 (Analog Devices) - 10

link to page 10 LTC4007
OPERATION 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 for FLAG = Restart LOW Terminated by expired timer >BAT LOW HIGH HIGH HIGH HIGH LOW >T HIGH (Waiting for Restart Charge termination defeated X X X X X X X 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. to keep a low forward voltage drop from drain to source. current comparator IREV or the beginning of the next If the voltage between DCIN and CLN drops to less than cycle. The oscillator uses the equation: 25mV, the input FET is turned off slowly. If the voltage V between DCIN and CLN is ever less than –25mV, then the t DCIN – VBAT OFF = input FET is turned off in less than 10µs to prevent sig- VDCIN • fOSC nificant reverse current from flowing in the input FET. In to set the bottom MOSFET on time. The result is a nearly this condition, the ACP pin is driven low and the charger constant switching frequency over a wide input/output is disabled. voltage range. This activity is diagrammed in Figure 1.
Battery Charger Controller
OFF TGATE The LTC4007 charger controller uses a constant off- ON time, current mode step-down architecture. During nor- ON mal operation, the top MOSFET is turned on each cycle BGATE tOFF when the oscillator sets the SR latch and turned off OFF when the main current comparator I TRIP POINT SET BY ITH VOLTAGE CMP resets the SR latch. While the top MOSFET is off, the bottom MOSFET INDUCTOR CURRENT is turned on until either the inductor current trips the 4006 F01
Figure 1.
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