Datasheet LTC4008 (Analog Devices) - 9

LTC4008
TEST CIRCUIT
VFB 7 LTC4008 + VREF + – EA – BATMON CSP BAT ITH 13 11 12 9 90.325k + LT1055 9.675k – 0.6V 4008 TC
OPERATION OVERVIEW
As the battery approaches the final float voltage, the The LTC4008 is a synchronous current mode PWM step charge current will begin to decrease. When the current down (buck) switcher battery charger controller. The drops to 10% of the full-scale charge current, an internal charge current is programmed by the combination of a C/10 comparator will indicate this condition by latching program resistor (R the FLAG pin low. If this condition is caused by an input PROG) from the PROG pin to ground and a sense resistor (R current limit condition, described below, then the FLAG SENSE) between the CSP and BAT pins. The final float voltage is programmed with an exter- indicator will be inhibited. When the input voltage is not nal resistor divider and the internal 1.19V reference volt- present, the charger goes into a sleep mode, dropping age. Charging begins when the potential at the DCIN pin battery current drain to 15µA. This greatly reduces the rises above the voltage at BAT (and the UVLO voltage) current drain on the battery and increases the standby and the ACP/SHDN pin is high. An external thermistor time. The charger can be inhibited at any time by forcing network is sampled at regular intervals. If the thermistor the ACP/SHDN pin to a low voltage. Forcing ACP/SHDN value exceeds design limits, charging is suspended and low, or removing the voltage from DCIN, will also clear the FAULT pin is set low. If the thermistor value returns the FLAG pin if it is low. to an acceptable value, charging resumes and the FAULT pin is set high. An external resistor on the RT pin sets the sampling interval for the thermistor.
Table 1. Truth Table For Indicator States MODE DCIN ACP/SHDN FLAG** FAULT** ICL
Shutdown by low adapter voltage (Disabled on LTC4008-1) <BAT LOW HIGH HIGH LOW Normal charging >BAT HIGH HIGH HIGH* HIGH* Input current limited charging >BAT HIGH HIGH* HIGH* LOW Charger shut down due to thermistor out of range >BAT HIGH X LOW HIGH Shut down by ACP/SHDN pin (USER) X Forced LOW HIGH HIGH LOW Shut down by undervoltage lockout >BAT + <UVL HIGH HIGH HIGH* LOW *Most probable condition, **Open-drain output, HIGH = Open with pull-up, X = Don’t care Rev C For more information www.analog.com 9 Document Outline Description Typical Application Absolute Maximum Ratings Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Typical Application Related Parts Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Test Circuit Operation Applications Information Package Description Revision History Related Parts