
NCP5008, NCP5009
Set Up Output Current Range
V bat
1
V bat
1
+
BandGap
I ref
?
V bat
GND
I ref
R ref
30 k
V bat
Iphoto
1
1:746
Iout Reference
= (I ref ?Iphoto)*746*(Bn+0.5)
GND
1
V bat
1
I = (I ref ?Iphoto)*(Bn+0.5)
1
1
1
1:Bn
2:1
+
BandGap
?
GND
GND GND
GND
GND
GND
Photo
Q1
NPN?PHOTO
GND
Figure 20. Functional Diagram
Iref + 1.24
The current sunk to ground on PHOTO pin is subtracted
from the current sunk to ground on I ref 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:
Where k = 746, Bn represents the bit of the internal shift
register, range from 1 to 7, and Ivalley = (I ref ? Iphoto)
* 0.5 * k.
We can write also Ipeak = (I ref ? Iphoto) * (Bn + 0.5) * k.
Please find below the formula to quickly calculate R1
resistor (resistor on I ref pin):
R1
Ipeak = Ivalley + (I ref ? Iphoto) * Bn * k.
http://onsemi.com
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