The MODE pin controls the state of an internal 370uA current reference (IREF). When active (MODE pin low),the total current sourced out of CHP is IVOUT/1 000 +IREF. The primary function of the current reference is to offset the battery charger charge current for lOOmA mode. When MODE is high, the current reference is disabled. The total current out of CHP with MODE high is IVOUT/1000. The MODE controlled current offset makes it possible to con- figure the batte ry charger and the LTC4410 to support the USB specification l.0 and 2.0 requiredlOOmAand 500mA modes of operation.
The TS317L is a 3-terminal floating regulator. In operation, the TS317L develops and maintains a nominal l.25V reference (Vref) between its output and adjustment terminals. This reference voltage is converted to a programming current (lprog.) by Ri (see Figure 17), and this constant current flows through R2 to ground. The regulated output voltage is given by: Vout = Vref ( 1 + R2 / R1 ) +ladj * R2 Since the current from the adjustment terminal (ladj) represents an error term in the equation, the TS317L was designed to control ladj to less than 100uA and keep it constant. To do this, all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise. Since the TS317L is a floating regulator, it is only the voltage differential across the circuit which is important to performance, and operation at high voltages with respect to ground is possible.
