Rainbow Electronics DS4412 - Manual (Page 9)

DS4412
Dual-Channel, I
2
C Adjustable
Sink/Source Current DAC
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Application Information
Example Calculation
for an Adjustable Power Supply
In this example, the Typical Operating Circuit is used
as a base to create Figure 3, a 2.0V voltage supply with
±20% margin. The adjustable power supply has a
DC-DC converter output voltage, V
OUT
, of 2.0V and a
DC-DC converter feedback voltage, V
FB
, of 0.8V. To
determine the relationship of R 0A and R 0B , we start with
the equation:
Substituting V FB = 0.8V and V OUT = 2.0V, the relation-
ship between R 0A and R 0B is determined to be:
R 0A = 1.5 x R 0B
I OUT0 is chosen to be 1mA (midrange source/sink cur-
rent for the DS4412). Summing the currents into the
feedback node, we have the following
Where:
And
To create a 20% margin in the supply voltage, the value
of V
OUT is set to 2.4V. With these values in place, R 0B is
calculated to be 267
Ω, and R
0A is calculated to be 400
Ω.
The current DAC in this configuration allows the output
voltage to be moved linearly from 1.6V to 2.4V using 15
settings. This corresponds to a resolution of 25.8mV/step.
V CC Decoupling
To achieve the best results when using the DS4412,
decouple the power supply with a 0.01µF or 0.1µF
capacitor. Use a high-quality ceramic surface-mount
capacitor if possible. Surface-mount components mini-
mize lead inductance, which improves performance,
and ceramic capacitors tend to have adequate high-
frequency response for decoupling applications.
I
V V
R
R A
OUT FB
A
0
0
=
−
I
V
R
R B
FB
B
0
0
=
I I I
OUT R B R A 0 0 0
= −
V
R
R R
V
FB
B
A B
OUT
=
+
× 0
0 0
DC-DC
CONVERTER
FB
OUT
SDA
SCL
OUT0
GND
R
FS0
= 4.612k Ω
4.7k Ω 4.7k Ω
V CC
V CC V OUT = 2.0V
FS0
R 0B = 267 Ω
R 0A = 400 Ω
V FB = 0.8V
I R0A
I
R0B
I OUT0
DS4412
Figure 3. Example Application Circuit
Package Information
For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo .