ZXLD1370EST16TC datasheet(32/40 Pages) DIODES

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ZXLD1370

Document number: DS32165 Rev. 6 - 2

32 of 40

www.diodes.com

December 2016

ZXLD1370

Application Information (Cont.)

Overvoltage Protection

The ZXLD1370 is inherently protected against open-circuit load when used in Buck configuration. However, care has to be taken with open-

circuit load conditions in Buck-Boost or Boost configurations. This is because in these configurations there is no internal open-circuit protection

mechanism for the external MOSFET. In this case an Overvoltage Protection (OVP) network should be provided externally to the MOSFET to

avoid damage due to open circuit conditions. This is shown in Figure 38 below, highlighted in the dotted blue box.

Figure 38 OVP circuit

The zener voltage is determined according to: VZ = VLEDMAX +10% where VLEDMAX is maximum LED chain voltage.

If the LEDA voltage exceeds VZ the gate of MOSFET Q2 will rise turning Q2 on. This will pull the PWM pin low and switch off Q1 until the voltage

on the drain of Q1 falls below VZ. If the voltage at LEDA remains above VZ for longer than 20ms then the ZXLD1370 will enter into a shutdown

state.

Care should be taken such that the maximum gate voltage of the Q2 MOSFET is not exceeded.

Take care of the max voltage drop on the Q2 MOSFET gate.

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