SDAA108 October 2025 LM5171
6 Constant Current Operation with ISETx Clamping
CC/CV charging is a popular method of charging batteries. The average current mode control provides a simple way to achieve constant current operation: clamping the ISETx voltage.
Clamping ISETx with TLV431 is shown in Figure 6-1. The resistor divider sets the ISETx clamping voltage Vclamp to,
Figure 6-1 ISETx Clamping with TLV431The charging current, battery voltage, ERRLV voltage and ISETx voltage are shown in Figure 6-2. In CC mode, the ISETx voltage is clamped to Vclamp. When the battery voltage reaches the target voltage, the converter enters CV mode. The output of the error amplifier drops and the ISETx voltage drops to less than Vclamp, the charging current is determined by the CV loop.
Figure 6-2 CCCV with ISETx ClampingWhen an adjustable constant current is desired, clamp ISETx with an op amp as shown in Figure 6-3. The ISETx clamping voltage Vclamp follows ISETinput,
Figure 6-3 ISET Clamping with Op Amp