8.4.2 Mode Detection

The magnitude of the PWM signal is used to determine which dimming mode the device enters. The internal peak detector at the PWM pin holds the magnitude of the PWM signal. Once the device is enabled, after 300-µs delay, the output of the peak detector is compared with two voltage thresholds, V_ADIM and V_PDIM, which are 1 V and 2.07 V, respectively. If the output of the peak detector is higher than 2.07 V, analog dimming mode is chosen and locked. If the output is between 1 V and 2.07 V, PWM dimming mode is chosen and locked. If the output is less than 1 V, the device waits another 300 µs and compares again, and this process repeats until at least one mode is chosen and locked. See Figure 17 and Table 1 for reference. After the mode is detected and locked, soft start begins, the output voltage ramps up, and the LED current is regulated at the target value. The dimming mode cannot be changed unless VIN or PWM is cycled. section

Figure 17. Mode Detection Circuit