AS3833 Datasheet, PDF (11/21 Pages) ams AG – 6 channel high-precision LED cont rol ler for 3D-LCD backl ight with integrated step-up cont rol ler

AS3833
Datasheet - Detailed Description
8 Detailed Description
8.1 Precision current output
Figure 9. Current output stage
AG ^{t still valid} _{The LED-current is derived from either Rset using the following equation}
ms ^{ten ILED = RATIO × Iset}
=
RATIO × ^V----^s---^e--^t
R_set
=
500 × -1---.-2---V---
R_SET
(EQ 1)
a _{on Iset is protected against a short to ground. In the case of a ground short the current Iset is limited to 660uA and the LED-current to 330mA.}
I_set has a lower limit of 6uA with a 1uA hysteresis.This sets the lower limit of the LED-current to 3mA with R_set=200kΩ. If R_set is large than
c _{200kΩ, the LED-current is set to 0mA.}
l _{8.1.1 Phase shift}
a ^{The outputs are controlled by the PWM-input and a built in phase shift generator. All outputs are phase shifted by 1/6 of the PWM-period. In}
order to calculate the phase shift timing, two PWM-periods are needed. This means that after changing the PWM-frequency, the phase shift is
ic ^{updated after the second period. The PWM-frequency must be in the range from 60Hz to 1kHz.}
Techn ^{Figure 10. Phase shift}
Revision 1.8
10 - 20