LTC4007 TYPICAL APPLICATIO U APPLICATIO S U DESCRIPTIO ...

More documents

Recommendations

Info

LTC4007 BLOCK DIAGRA Q3 R CL Q1 Q2 L1 V IN 8 5k 15nF 0.1µF 20µF DCIN FLAG 17 GND 3C4C 6 7 CHEM 16 LOBAT 1 INFET 23 ACP 3 SHDN 24 FAULT 5 8 CLP 18 100mV CLN 19 ICL 13 TGATE 20 BGATE 22 PGND 21 – CLN 5.8V CL1 W 708mV 1.19V g m = 1.4m Ω MUX 1.105V + – + – EA gm = 1m Ω RESTART TIMER/CONTROLLER +– OSCILLATOR WATCHDOG DETECT tOFF + – DCIN PWM LOGIC 1.28V S Q R CHARGE CLN OV – + gm = 1m Ω ÷5 I CMP I REV 35mV CA2 BUFFERED ITH TBAD – + CA1 + – + – + – + C/10 OSCILLATOR THERMISTOR 11.67µA 1.19V – + – + 17mV 9k 397mV 2 CHG 4 RT RRT 9 NTC BAT 15 CSP 14 ITH 10 PROG 11 32.4k 0.47µF 0.0047µF 3k 3k 6K 0.12µF RSENSE R PROG 26.7k 10k NTC 4007 BD 20µF 4007f
TEST CIRCUIT OPERATIO U CHEM 16 7 3C4C CSP 14 DIVIDER/ MUX BAT 15 Overview The LTC4007 is a synchronous current mode PWM stepdown (buck) switcher battery charger controller. The charge current is programmed by the combination of a program resistor (RPROG) from the PROG pin to ground and a sense resistor (RSENSE) between the CSP and BAT pins. The final float voltage is programmed to one of four values (12.3V, 12.6V, 16.4V, 16.8V) with ±1% maximum accuracy using pins 3C4C and CHEM. Charging begins when the potential at the DCIN pin rises above the voltage at BAT (and the UVLO voltage) and the SHDN pin is low; the CHG pin is set low. At the beginning of the charge cycle, if the cell voltage is below 2.5V (2.44V if CHEM is low), the LOBAT pin will be low. The LOBAT indicator can be used to reduce the charging current to a low value, typically 10% of full scale. If the cell voltage stays below 2.5V for 25% of the total charge time, the charge sequence will be terminated immediately and the FAULT pin will be set low. An external thermistor network is sampled at regular intervals. If the thermistor value exceeds design limits, charging is suspended and the FAULT pin is set low. If the thermistor value returns to an acceptable value, charging resumes and the FAULT pin is set high. An external resistor on the RT pin sets the total charge time. The timer can be defeated by forcing the CHG pin to a low voltage. As the battery approaches the final float voltage, the charge current will begin to decrease. When the current drops to 10% of the full-scale charge current, an internal VREF + – EA LT1055 + – LTC4007 ITH 10 4007 TC 0.6V LTC4007 C/10 comparator will indicate this condition by latching the FLAG pin low. The charge timer is also reset to 1/4 of the total charge time when FLAG goes low. If this condition is caused by an input current limit condition, described below, then the FLAG indicator will be inhibited. When a time-out occurs, charging is terminated immediately and the CHG pin is forced to a high impedance state. The charger will automatically restart if the cell voltage is below 3.9V (or 3.81V if CHEM is low). To restart the charge cycle manually, simply remove the input voltage and reapply it, or set the SHDN pin high momentarily. When the input voltage is not present, the charger goes into a sleep mode, dropping battery current drain to 15μA. This greatly reduces the current drain on the battery and increases the standby time. The charger is inhibited any time the SHDN pin is high. Input FET The input FET circuit performs two functions. It enables the charger if the input voltage is higher than the CLN pin and provides the logic indicator of AC present on the ACP pin. It controls the gate of the input FET to keep a low forward voltage drop when charging and also prevents reverse current flow through the input FET. If the input voltage is less than VCLN, it must go at least 170mV higher than VCLN to activate the charger. When this occurs the ACP pin is released and pulled up with an external load to indicate that the adapter is present. The 4007f 9
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: PI FU CTIO S U U U ITH (Pin 10): Co
Page 11 and 12: OPERATIO U The peak inductor curren
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

LTC4007 TYPICAL APPLICATIO U APPLICATIO S U DESCRIPTIO ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?