NCP5008 データシートの表示（PDF） - ON Semiconductor

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NCP5008

Backlight LED Boost Driver

ON Semiconductor 

Set Up Output Current Range

Vbat

NCP5008, NCP5009

1

Iref

Rref

30 k

GND

1

1

Vbat

Iref

+

BandGap

−

GND

Vbat

Iphoto

Vbat

+

−

1

1

BandGap

GND

11

GND GND

Vbat

1

1:746

Iout Reference

= (Iref−Iphoto)*746*(Bn+0.5)

I = (Iref−Iphoto)*(Bn+0.5)

1:Bn

2:1

GND

GND

Photo

Q1

NPN−PHOTO

GND

GND

Figure 20. Functional Diagram

The current sunk to ground on PHOTO pin is subtracted

from the current sunk to ground on Iref pin. The result is

multiplied by the programmed value (Bn) and then

multiplied by the constant factor ratio (k = 746) in the

current mirror.

The constant factor k is a ratio between the current on

Iout sense and the Iout reference internally fixed.

The output current reference is:

Ipeak = Ivalley + (Iref − Iphoto) * Bn * k.

Where k = 746, Bn represents the bit of the internal shift

register, range from 1 to 7, and Ivalley = (Iref − Iphoto)

* 0.5 * k.

We can write also Ipeak = (Iref − Iphoto) * (Bn + 0.5) * k.

Please find below the formula to quickly calculate R1

resistor (resistor on Iref pin):

Iref

+

1.24

R1

http://onsemi.com

10

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