an30888b Panasonic Corporation of North America, an30888b Datasheet - Page 26

• Manufacturer Part Number: an30888b
• Description: High Brightness Led Driver Ic
• Manufacturer: Panasonic Corporation of North America

AN30888B
Technical Data (continued)
Functions and properties descriptions (continued)
(8) Soft start
Soft start circuit is incorporated into this IC to avoid high in-rush current during start-up.
After the device is enabled (ENB = High), the output inductor current and output voltage will rise slowly from initial condition. This
slow start-up time ensure smooth start-up as well as minimize in-rush current.
(9) Over Voltage Protection (OVP)
When operating in Boost mode or Buck-Boost mode, over voltage protection is needed to prevent damages to IC or external component
damages in cases of open LED condition.
OVP switches off external power MOSFET to prevent output from rising over a designed OVP voltage. Output voltage should be
limited to the rating of external component used. (for example Drain Source voltage rating of the external MOSFET or the output
capacitor)
OVP compares the internal reference voltage of 1.26 V with output voltage through resistor network.
OVP threshold is set using the following equation:
1.262 V × (R1 ＋R2)
V
= —————————— ……………………
Eq[11]
(Boost mode，Buck-Boost mode)
OVP
R2
If R1 = 470 kΩ, R2 = 30 kΩ, OVP threshold will be designed at around 21 V.
When OVP is triggered, output voltage will be clamped at this threshold voltage (with hysteresis of around 1 V to 2 V) until the fault
(e.g open LED condition) has been removed.
When operating in buck mode, the OVP pin must be short to ground to disable this function as OVP function is not necessary in this
mode.
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