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LTC4007-1 Datasheet(PDF) 11 Page - Linear Technology |
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LTC4007-1 Datasheet(HTML) 11 Page - Linear Technology |
11 / 24 page 11 LTC4007-1 40071f gate of the input FET is driven to a voltage sufficient to keep 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 LTC4007-1 charger controller uses a constant off- time, current mode step-down architecture. During nor- mal operation, 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 com- parator 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. The peak inductor current, at which ICMP resets the SR latch, is controlled by the voltage on ITH. ITH is in turn controlled by several loops, depending upon the situation at hand. The average current control loop converts the voltage between CSP and BAT to a representative current. Error amp CA2 compares this current against the desired current programmed by RPROG at the PROG pin and TGATE OFF ON BGATE INDUCTOR CURRENT tOFF TRIP POINT SET BY ITH VOLTAGE ON OFF 40071 F01 Figure 1 OPERATIO LTC4007-1: State Diagram 40071 TBL01 MASTER SHUTDOWN SHUTDOWN ANY 1 2 4 11 12, 13, 14, 15, 16 3, 17, 18, 19, 20, 21 3, 8, 9, 10 5, 6, 7 CONDITION CHARGE |
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Similar Description - LTC4007-1 |
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