ZXLD1374

ZXLD1374

Document number: DS35032 Rev. 1 - 2

Page 29 of 35

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October 2010

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Over-voltage Protection

The ZXLD1374 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 only an over-voltage FLAG but no internal open-circuit protection mechanism for the internal MOSFET. In this case an

Over-Voltage-Protection (OVP) network should be provided to the MOSFET to avoid damage due to open circuit conditions.

This is shown in Figure 37 below, highlighted in the dotted blue box.

Figure 50. OVP Circuit

The zener voltage

MOSFET Q2 will start to turn on causing the PWM pin to be brought low. This will disable to LX output until the voltage on

the LX falls below Vz. If the fault exists for longer than 20ms then the ZXLD1374 will enter into a shutdown state.

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

Alternatively, to perform the OVP function, it can be used the diagnostic section of the ZXLD1374. In particular a

microcontroller can read the FLAG and the status pins, and if they signal an over-voltage, the microcontroller can switch the

device off by pulling the PWM signal low.