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Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

48102.002

LED Drivers

LC5200 Series

Functional Description

Regulator

The LC5200 series provides 12 V output voltage, generated

from the supply voltage on the VBB pin, which is used to power

internal circuits and external components. When the gate capaci-

tance charging of the MOSFET occurs, it generates a current

surge, which results in ripple voltage. This could affect operation,

therefore, connect a 0.1 μF ceramic capacitor at the REG pin to

stabilize operation.

Current Control

Current control is done by a fixed off-time PWM topology. The

output current level can be set by the input voltage on the REF

pin, and voltage across the current sense resistor at the SENSE

pin. In addition, the fixed off-time can be adjusted by the values

selected for the external capacitor and resistor at the TOFF pin.

UVLO (Undervoltage Lock Out)

This prevents the device from malfunctioning by shutting down

the output circuit when the internal supply voltage becomes lower

circuit is used for the power-on reset function of overcurrent

protection (OCP).

TSD (Thermal Shutdown)

When the main control chip (MIC) temperature exceeds the TSD

tem logic continues to operate), in order to avoid abnormal tem-

perature increase. When the temperature drops by the hysteresis

returns to normal operation. Note: The primary source of heating

is the MOSFET, and there is a delay while the heat spreads to the

MIC and is sensed. Therefore, a rapid temperature increase of the

MOSFET may damage the device.

OCP (Overcurrent Protection)

When the SENSE pin input voltage reaches the OCP threshold,

to release from latch mode, cycle the device power supply.

Note: OCP is for protecting the device from excess current. OCP

may not work at an LED-short condition because the coil may

suppress current increase.

Internal Switching Logic

The device turns the MOSFET gate driver circuit on or off based

on the status of the current control sensing circuit and the protec-

tion circuits.

Gate-Driver Operation

This comprises the MOSFET gate driver circuit.

The two device versions in the LC5200 series are distinguished

from each other by the MOSFET current rating. Select the current

rating that best matches the application circuit.