ZHCSBB4B July 2013 – June 2017 TPS61197
PRODUCTION DATA.
Use a resistor divider to program the maximum output voltage of the boost converter. To ensure the LED string can be turned on with setting current, the maximum output voltage must be higher than the forward voltage drop of the LED string. The maximum required voltage can be calculated by multiplying the maximum LED forward voltage (VFWD(max) ) and number (n) of series LEDs , and adding extra 2 V to account for regulation and resistor tolerances and load transients.
The recommended bottom feedback resistor of the resistor divider (R4 in Figure 18) is 20 kΩ. Calculate the top feedback resistor (R3 in the Figure 18) using Equation 5, where VOUT_OVP is the output overvoltage protection threshold of the boost converter.
When the device detects that the OVP pin voltage exceeds the overvoltage protection threshold of 3.04 V, indicating that the output voltage has exceeded the over-voltage proteciton threshold, the TPS61197 clamps the output voltage to prevent it going up any more. If the OVP pin voltage does not drop below the OVP threshold for more than 640 ms, the TPS61197 is latched off until the input power or the EN pin is re-cycled.