AS3691

Datasheet

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Revision 2.3

12 - 22

8

Detailed Functional Description

The AS3691 includes four high precision current sources (sinks). Each current source is set by an external

resistor. For internal power supply an internal shunt regulator is used. Optionally an additional 5V device can be

supplied as well with this shunt regulator.

The current sources are individually controlled by four ON inputs. If the inputs ON are high or left open, then the

current is set as follows:

Setting the input ON to low the current is

The current is not zero to avoid high voltage jumps on the LEDs and supplies and therefore reduce EMI.

8.1 Shunt Regulator

The supply of the AS3691 is generated from the high voltage supply. To obtain a 5V regulated supply, a series

resistor Rvdd is used together with an internal zener diode (shunt regulator principle). An external capacitor

Cvdd is used to filter the supply on the pin VREG.

The external resistor Rvdd has to be choosen according to the following formula:

possible to supply the AS3691 directly. In this case remove the resistor Rvdd and connected this supply directly

to VREG.

8.2 Overtemperature Protection

4

1

4

1

250

−

Ri

mV

ICURR

4

1

4

1

0

.

10

−

Ri

mV

ICURR

MAX

MAX

MIN

IVREG

VVREGINT

VDD

Rvdd

−

=

supply, where Rvdd is connected

4

1

4

1

4

1

4

1

0

.

0

−

−

−

−

=

+

=

I

I

Ri

mV

ICURR

for part numbers starting

with AS3691A

(see above Figure 11)