LTC4007 TYPICAL APPLICATIO U APPLICATIO S U DESCRIPTIO ...

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<strong>LTC4007</strong> OPERATIO U Table 1. Truth Table For Indicator States MODE DCIN SHDN ACP** LOBAT FLAG** FAULT** ICL TIMER STATE CHG** Shut down by low adapter voltage 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 (from NTC) HIGH Paused LOW 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 = LOW for Restart) Terminated by expired timer >BAT LOW HIGH HIGH HIGH HIGH LOW >T HIGH (Waiting for Restart Timer defeated X X X X X X X X Forced LOW Shut down by undervoltage lockout >BAT +
OPERATIO U 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 adjusts ITH until: VREF VCSP – VBAT + 11. 67μA• 3. 01kΩ = R 301 . kΩ PROG therefore, I CHARGE MAX ⎛ VREF ⎞ 301 . kΩ ( ) = ⎜ – 11. 67μA⎟ • ⎝R⎠ R PROG SENSE The voltage at BAT is divided down by an internal resistor divider and is used by error amp EA to decrease ITH if the divider voltage is above the 1.19V reference. When the charging current begins to decrease, the voltage at PROG will decrease in direct proportion. The voltage at PROG is then given by: RPROG VPROG = ( ICHARGE • RSENSE + 11. 67μA• 3. 01kΩ) • 301 . kΩ VPROG is plotted in Figure 2. The amplifier CL1 monitors and limits the input current, normally from the AC adapter to a preset level (100mV/ RCL). At input current limit, CL1 will decrease the ITH VPROG (V) 1.2 1.19V 1.0 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 ICHARGE (% OF MAXIMUM CURRENT) Figure 2. V PROG vs I CHARGE 4007 F02 0.309V <strong>LTC4007</strong> voltage, thereby reducing charging current. The ICL indicator output will go low when this condition is detected and the FLAG indicator will be inhibited if it is not already LOW. If the charging current decreases below 10% to 15% of programmed current while engaged in input current limiting, BGATE will be forced low to prevent the charger from discharging the battery. Audible noise can occur in this mode of operation. An overvoltage comparator guards against voltage transient overshoots (>7% of programmed value). In this case, both MOSFETs are turned off until the overvoltage condition is cleared. This feature is useful for batteries which “load dump” themselves by opening their protection switch to perform functions such as calibration or pulse mode charging. PWM Watchdog Timer There is a watchdog timer that observes the activity on the BGATE and TGATE pins. If TGATE stops switching for more than 40μs, the watchdog activates and turns off the top MOSFET for about 400ns. The watchdog engages to prevent very low frequency operation in dropout—a potential source of audible noise when using ceramic input and output capacitors. Charger Start-Up When the charger is enabled, it will not begin switching until the ITH voltage exceeds a threshold that assures initial current will be positive. This threshold is 5% to 15% of the maximum programmed current. After the charger begins switching, the various loops will control the current at a level that is higher or lower than the initial current. The duration of this transient condition depends upon the loop compensation, but is typically less than 100μs. Thermistor Detection The thermistor detection circuit is shown in Figure 3. It requires an external resistor and capacitor in order to function properly. The thermistor detector performs a sample-and-hold function. An internal clock, whose frequency is determined by 4007f 11
Page 1 and 2: FEATURES ■ Complete Charger Contr
Page 3 and 4: ELECTRICAL CHARACTERISTICS The ●
Page 5 and 6: TYPICAL PERFOR A CE CHARACTERISTICS
Page 7 and 8: PI FU CTIO S U U U ITH (Pin 10): Co
Page 9: TEST CIRCUIT OPERATIO U CHEM 16 7 3
Page 13 and 14: APPLICATIO S I FOR ATIO U W U U Bat
Page 15 and 16: APPLICATIO S I FOR ATIO used when t
Page 17 and 18: APPLICATIO S I FOR ATIO U W U U Ada
Page 19 and 20: APPLICATIO S I FOR ATIO U W U U Dis
Page 21 and 22: APPLICATIO S I FOR ATIO LOBAT ICL A
Page 23 and 24: PACKAGE DESCRIPTION U .254 MIN .016

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