AS3820 datasheet(11/52 Pages) DIALOG

11 / 52 page

AS3820

16-Channel White LED Controller for LCD Backlight

Rev. 1.1

Datasheet

www.dialog-semiconductor.com

11 of 52

05-Feb-2019

8 Detailed Description

This section provides a detailed description of the device related components.

8.1 Current Outputs

Figure 8.1 : Detailed Block Diagram of Precision Current Sink

8.1.1 Precision Current Sink

All current sinks are built with an internal error amplifier A1 and an external power transistor. The external transistor

can either be a NMOS or a NPN bipolar transistor. For low EMI radiation the slew rate of the amplifier output voltage

can be adjusted.

8.1.2 Power Supply Feedback

The gate driving voltage for the external transistor is monitored to adjust the power supply output. If this voltage gets

to high a comparator enables counting up of the “idac_fbX_counter” with 256μs clock speed. This increases the output

current of the FB-IDAC and so the output voltage of the external power supply can be increased via pin FB1 or pin

FB2. The feedback function of each output can be assigned to either FB1 or FB2. The power supply feedback can be

turned OFF for every current channel separately.

8.1.3 Manual Control of the External Power Supply Voltage

The counter value “idac_fbX_counter” can also be preset by software if “fbcounter_man_fx” =1. This enables software

control of the external power supply output voltage.

AS3820 데이터시트(PDF) 11 Page - Dialog Semiconductor