MCP1643 datasheet(11/28 Pages) MICROCHIP

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DS20005208B-page 11

MCP1643

4.2.6

INTERNAL COMPENSATION

The error amplifier, with its associated compensation

network, completes the closed loop system by

comparing the voltage from the sense resistor to a

120 mV reference at the input of the error amplifier and

feeding the amplified and inverted signal to the control

input of the inner current loop. The compensation net-

work provides phase leads and lags at appropriate fre-

quencies to cancel excessive phase lags and leads of

the power circuit. All necessary compensation compo-

nents and slope compensation are integrated.

4.2.7

SHORT CIRCUIT PROTECTION

Unlike most boost converters, the MCP1643 LED Con-

stant Current Driver allows its output to be shorted

during normal operation. The internal current limit and

overtemperature protection limit excessive stress and

protect the device during periods of short circuit, over-

current and overtemperature.

4.2.8

OUTPUT OVERVOLTAGE

PROTECTION

Overvoltage Protection is designed to protect the

MCP1643 if the output voltage (VOUT) becomes higher

than 5.0V. Because the device is a step-up converter

that runs as a constant current generator, if the load is

disconnected, the output increases up to dangerous

voltages. This happens when the LED fails. The device

stops switching and the VOUT value is verified periodi-

cally if it is higher than 5.0V (see Figure 2-18).

This feature does not protect the LED. An optional

Zener diode is added between VOUT and VFB pins to

clamp the output voltage and protects the LED against

excessive voltage and current.

4.2.9

OVERTEMPERATURE

PROTECTION

Overtemperature protection circuitry is integrated in the

MCP1643 LED Constant Current Driver. This circuitry

monitors the device junction temperature and shuts the

device off if the junction temperature exceeds the typi-

cal +150°C threshold. If this threshold is exceeded, the

device will automatically restart once the junction tem-

perature drops by 25°C.

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