ZHCSBB4B July 2013 – June 2017 TPS61197
PRODUCTION DATA.
The TPS61197 regulates the output voltage with peak current mode PWM control. The control circuitry turns on an external switch FET at the beginning of each switching cycle. The input voltage is applied across the inductor and stores the energy as the inductor current ramps up. During this portion of the switching cycle, the load current is provided by the output capacitor. When the inductor current rises to the threshold set by the error amplifier (EA) output, the switch FET is turned off and the external Schottky diode is forward biased. The inductor transfers stored energy to replenish the output capacitor and supply the load current. This operation repeats each switching cycle. The switching frequency is programmed by an external resistor.
A ramp signal from the oscillator is added to the current ramp to provide slope compensation, shown in the Functional Block Diagram. The duty cycle of the converter is then determined by the PWM logic block which compares the EA output and the slope compensated current ramp. The feedback loop regulates the OVP pin to a reference voltage generated by the current regulation control circuit which senses the LED current at the IFB pin. The output of the EA is connected to the COMP pin. An external RC compensation network must be connected to the COMP pin to optimize the feedback loop for stability and transient response.
The TPS61197 consistently adjusts the boost output voltage to account for any changes in LED forward voltages. In the event that the boost controller is not able to regulate the output voltage due to the minimum pulse width (ton(min), in the Electrical Characteristics table), the TPS61197 enters pulse skip mode. In this mode, the device keeps the power switch off for several switching cycles to prevent the output voltage from rising above the regulated voltage. This operation typically occurs in light load condition or when the input voltage is higher than the output voltage.