MAX684 charge pump driving white LED circuit diagram

The MAX684 charge pump drives the white LED circuit as shown in the figure. When the MAX684 charge pump operates within the input voltage range of 2.7 to 4.21/, it can produce a 5V/50mA (max) output, and only requires one additional resistor and three capacitors, eliminating the need for an inductor. If more than 3 white LEDs are needed in actual applications, MAX683 and MAX682 can be used, which can provide 100mA and 250mA output currents respectively. Among them, MAX682 can drive up to 16 parallel white LEDs.

To control the brightness of the white LED, you can add a PWM signal with a frequency range of 200 to 300Hz to the SHDN pin. After selecting the switching frequency of MAX*, the value of the external resistor REXT can be calculated according to the following formula.

Figure MAX684 charge pump driving white LED circuit