Datasheet

LED Error Detection

To measure VF of an LED set PWM = 100% for the LED and set the desired LED current with the current slider. Disable temperature

compensation. On LED test portion tag Start conversion and Continuous measurement. Click on RD button to read the test result

from LP5523’s internal register. Try with different current settings and compare the result with the value specified by the manu-

facturer. If there is a short to ground in the LED circuit the result is ~0V and if there is an open the result is ~4,5V. This feature can

also be addressed to measure the voltage on VDD, VOUT and INT pins. Typical example usage includes monitoring battery voltage

or using INT pin as a light sensor interface (A/D converter value can be used as a variable in program control).

Charge Pump Gain Control

Charge pump gain can be forced to 1x, 1.5x, or you can let the LP5523 decide the best charge pump gain based on LED forward

voltage requirements by selecting AUTO mode (this is the most useful setting in real applications). Note that outputs D7, D8, and

D9 are powered directly from VDD and they have no effect on gain change decision-making. LP5523 charge pump has a gain

change hysteresis which prevents the mode from toggling back and forth (1x -> 1.5x -> 1x...), which would cause ripple on VIN and

LED flicker.

The hysteresis region width depends on the choice of threshold voltage. Threshold voltage is defined as follows VTHRESHOLD =

VDD - MAX(voltage on D1 to D6). If VTHRESHOLD is larger than the set value (100mV to 400mV), the charge pump is in 1x mode.

A good compromise solution between efficiency and performance is 200 mV. In addition to take the charge pump total load current

into account enable the adaptive hysteresis.

Timer enable activates forced mode change. In forced mode charge pump mode change from 1.5x to 1x is attempted at the constant

interval specified by the Timer control. With infinite setting the charge pump switches gain from 1x mode to 1.5x mode only. The

gain reset back to 1x is enabled under certain conditions, for example in the power-save mode. Forced mode and treshold pa-

rameters are used to optimize efficiency in a real design - it is desired that 1.5x gain is used only when needed.

AN-2227 - LP5523 Evaluation Kit