ZLED7025 datasheet(16/26 Pages) IDT

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ZSLS7025 Datasheet

April 20, 2016

OVP

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Operating Conditions

3.1

Under-Voltage Lockout

The under-voltage lockout (UVLO) function monitors the voltage on the ZSLS7025’s VDD pin. If this voltage is lower

than the UVLO threshold minus the UVLO hysteresis (VUVLO_TH - VUVLO_HYS), the ZSLS7025 is disabled.

If the voltage on the VDD pin reaches a level higher than the UVLO threshold (VUVLO_TH), the lock-out function turns

off and the ZSLS7025 is re-enabled. See parameters 1.3.2 and 1.3.3 in section 1.3 for the VUVLO_TH threshold and

VUVLO_HYS hysteresis, respectively.

3.2

Over-Voltage Protection

Open-load protection is achieved through the ZSLS7025's over-voltage protection (OVP). In boost converters, an

LED string failure can cause the feedback voltage (VFB) to always be zero. If this happens, the ZSLS7025 will keep

boosting the output voltage higher and higher. If the output voltage reaches the programmed OVP threshold, the

protection mechanism will be triggered and stop the switching action. To ensure that the circuit functions properly, the

OVP setting resistor divider, R1 and R2, must be set with appropriate values given by equation (13). The

recommended OVP voltage is either 1.25 times the normal output voltage or 5V higher than the normal output

voltage, whichever is higher.

(13)

Where

VOVP_TH = Over-voltage input threshold: 1.0V (typical; see parameter 1.3.12 in section 1.3)

VOVP = Output voltage OVP level

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