MAX1910 White LED Charge Pumps – Maxim IC

Drives LEDs with a regulated output voltage or current (up to 120mA) from an unregulated input supply (2.7V to 5.3V). These are complete DC-DC converters requiring only four small ceramic capacitors and no inductors. 200mV Current-Sense Threshold Reduces Power Loss.

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MAX1910 White LED Charge Pumps – Maxim IC

The MAX1910/MAX1912 are complete charge-pump boost converters requiring only four small ceramic capacitors. They employ a 750kHz fixed-frequency 50% duty-cycle clock.

Figure 4’s circuit improves LED current matching by raising the ballast resistance while maintaining a 200mV VSET. The increased ballast resistance tolerates wider LED mismatch, but reduces efficiency and raises the minimum input voltage required for regulation.

Yet another method of biasing LEDs is shown in Figure 5. In this case, the current through the complete parallel combination of LEDs is set by R5. R1–R4 are only used to compensate for LED variations. This method of biasing is useful for parallel LED arrays that do not allow connection to individual LEDs.