ZLED7015 datasheet(18/23 Pages) ETC2

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ZLED7015

1.0MHz Boost Converter with Internal 35V Switch

Data Sheet

December 20, 2011

— Rev. 1.00

the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice.

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OVP

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Operating Conditions

4.1

Under-Voltage Lockout

The under-voltage lockout (UVLO) monitors the

ZLED7015’s internal regulator output voltage, VP, to ensure

correct operation of the internal circuitry. When the VP voltage is lower than the UVLO threshold VUVLO, the

ZLED7015 disables the internal power switch. If the VP voltage reaches a level higher than the UVLO

threshold plus UVLO hysteresis (VUVLO+VUVLO_HYS) the UVLO turns off and the internal power switch is

re-enabled. See parameters 1.3.14 and 1.3.15 in section 1.3 for the UVLO threshold and hysteresis.

4.2

Over-Voltage Threshold and Open-Circuit Protection

If the LED string becomes open or the FB pin is shorted to ground, the ZLED7015 would normally continually

boost the output voltage to potentially damaging levels. To prevent this, the ZLED7015 includes an integrated

over-voltage protection (OVP) mechanism. If

the output voltage reaches the ZLED7015’s OVP threshold V

OVP,

the protection circuitry is triggered and the device automatically turns off the internal switch, stopping the

boost function and protecting the device. Once the output voltage falls below the OVP threshold minus OVP

threshold hysteresis (VOVP_TH-VOVP_TH_HYS), the device will enter soft-start mode.

The OVP threshold VOVP for the ZLED7015 is selectable via the R1 and R2 resistor values determined by

equation (5):

(5)

Where

VOVP = Over-voltage protection threshold

VOVP_TH = Internal over-voltage threshold reference voltage (see Table 1.3, parameter 1.3.16)

Important: Care must be taken to select proper R1 and R2 values to ensure proper functioning of the

ZLED7015. See specification 1.3.16 in Table 1.3 for the over-voltage protection threshold voltage. Set VOVP

3V higher than the normal operation output voltage.

Important: When setting VOVP, care must be taken to ensure VOUT cannot exceed 35V.

Minimize noise coupling on the OVP pin, which could interfere with proper protection, by connecting a 10nF

ceramic capacitor to GND from OVP (COVP).

4.3

Over-Temperature Protection

The ZLED7015 features on-chip over-temperature protection. If its internal temperature exceeds the over-

temperature protection (OTP) threshold, TOTP, due to high power dissipation and improper heat sinking, the

internal power switch is disabled. Once the internal temperature has fallen below the OTP threshold minus the

OTP threshold hysteresis (TOTP - TOTP_HYS), the ZLED7015 enters the soft-start mode (see section 2.1).

Refer to Table 1.1 for the maximum package power dissipation specifications for the ZLED7015

’s MSOP-10

package.

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