LED7706

Operation description - boost section

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6.4

Over voltage protection

An adjustable Over-Voltage Protection is available. It can be set feeding the OVSEL pin with

a partition of the output voltage. The voltage of the central tap of the divider is thus

compared to a fixed 1.234 V threshold. When the voltage on the OVSEL pin exceeds the OV

threshold, the FAULT pin is tied low (see Section 8 on page 25) and the device is turned off;

this condition is latched and the LED7706 is restarted

performing a Power-On Reset (the POR occurs when the LDO output falls below the lower

UVLO threshold and subsequently crosses the upper UVLO threshold during the rising

phase of the input voltage). Normally, the value of the high-side resistors of the divider must

be chosen as high as possible (but lower than 1 M

discharge when the boost converter is off (during the off phase of the dimming cycle). The

R2/R1 ratio is calculated to trigger the OVP circuitry as soon as the output voltage is 2 V

higher than the maximum value for a given LED string (see equation 3). Two additional

Equation 3

Equation 4

Figure 7.

OVP threshold setting

)

V

234

.

1

V

2

V

(

V

234

.

1

R

R

OVP

,

OUT

1

2

−

+

⋅

=

1

2

10

13

R

R

C

2

C

⋅

=

LX

OVSEL

SGND

LED7706