The precise reverse current limit of the device enables the LM5177 to charge a storage element on the input of the power stage. Once the integrated average current limitation circuit of the LM5177 is enabled on the input, the third regulation loop maintains a constant current operation to charge the storage on the input, for example, a battery or super-capacitor array. The end of charge voltage for the input is regulated by a simple hysteric regulation approach or by using a linear approach, with an external operational amplifier as well as an equivalent digital regulation scheme.

Once the system power supply is interrupted or has a malfunction the LM5177 immediately supplies the connected system load as soon the selected backup voltage threshold triggers. The seamless transition is maintained by the buck-boost voltage control loop, which stays in regulation during charging and allows for a minimum voltage drop for the connected system during backup.

Benefits:

• Seamless and automatic transition from main system supply to the power backup.
• Combination of energy storage charging control and backup regulator with a single chip application.
• Single inductor application, that is one power stage for charging and backup operation.
• Constant current and constant voltage operation is possible.
• Adjustable on-the-fly transition voltage using the output feedback divider.
• Scalable application for multiple systems. Power levels are adjusted with the BOM. Topologies and architecture qualification maintains the same.

Below details for the control loop interacting in the DC/DC backup application. The central point for the interaction is the COMP pin which defines the peak current target for the underlying bi-directional peak current control loop

1. Internal peak current loop - the control input signal from the COMP pin sets the bi-directional (positive and negative pack current) for the PWM logic.
2. The internal output voltage loop is controlling the V_o, when the system supply voltage drops below the selected voltage by the FB-PIN.
3. The internal constant current loop limits and regulates the peak current in the selected direction. For most power backup cases the negative (charging) current is selected. By activating the constant current limit, the peak current is clamped and does not reach the full value, enabling a lower charging current. The forward direction of the peak current is not limited if the negative direction of the constant current loop is selected.
4. The input voltage (V_BAT) constant voltage regulation is added externally with a linear regulator in the COMP-pin. Once the battery voltage reaches the desired target voltage, the regulator pulls up the peak current set-point and the charging operation stops.