AS3691

Datasheet

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Revision 2.3

15 - 22

A typical AS3691 for single color leds can be done as follows using automatic supply regulation (feedback path

UV):

Figure

15 – Typical AS3691 system for single color leds and supply regulation loop; serveral AS3691 can be cascaded

Note: Csup (100nF) is only required, if there are long wires (>0.3m) between the DCDC converter and the

AS3691. The wire length between the Csup capacitor and the CURRx pin on AS3691 should not exceed 0.3m.

If this cannot be guaranteed, add additional capacitors of 100nF to the pins CURRx.

9.1 Design Example

So for a current of 100mA, use a resistor of 2.5

Ω; 1/8W rated resistors are suitable (even up to 400mA).

Then calculate the required voltage of the power supply. The minimum voltage on the current sink for

As this is the required minimum voltage of the power supply, add all the tolerances on top. Assumed +/-10%

supply tolerance results in a power supply with nominal 13V (to have at least 11.81V in worst case).

Using the following formula to calculate the external shunt resistor

obtains 2564

Ω. The nearest lower(!) available value is 2.4kΩ. For Cvdd use

Csup (100nF) is only required, if there are long connections between the DCDC converter and the AS3691

(>0.3m). The wire length between the Csup capacitor and the CURRx pin on AS3691 should not exceed 0.3m. If

this cannot be guaranteed, add additional capacitors of 100nF to the pins CURRx.

4

1

4

1

250

−

ICURR

mV

Ri

mA

V

VDD

IVREG

VREGINT

VDD

Rvdd

MIN

MAX

MAX

MIN

5

.

2

4

.

5

−

=

−

=

nF

Cvdd

100

=

power supply, where Rvdd is connected

UV

VDD

Voltage Feedback

input for DCDC

DCDC Converter

for VDD

Overtemp

AS3691

D1

Vc

Vc

Vc

Vc

...

...

...

Main

supply

PWM

VSS

PWM

(optional)

5V powered

system

(optional)

Overtemp

AS3691

D1

...

Csup

100nF