EVAL-AD5821AEBZ Analog Devices Inc, EVAL-AD5821AEBZ Datasheet - Page 13

• Manufacturer Part Number: EVAL-AD5821AEBZ
• Description: Evaluation Board I.c.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5821AEBZ

• Number Of Dac's: 1
• Number Of Bits: 10
• Outputs And Type: 1, Single Ended
• Sampling Rate (per Second): 400k
• Data Interface: I²C
• Settling Time: 250µs
• Dac Type: Current
• Voltage Supply Source: Single
• Operating Temperature: -30°C ~ 80°C
• Utilized Ic / Part: AD5821A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

When sinking the maximum current of 120 mA, the maximum
voltage drop allowed across R
drain to source voltage of Q1 is 200 mV. This means that the
AD5821A output has a compliance voltage of 600 mV. If V
falls below 600 mV, the output transistor, Q1, can no longer
operate properly and I
When sinking 90 mA, the maximum voltage drop allowed across
R
Q1 is 180 mV. This means that the AD5821A output has a
compliance voltage of 480 mV. If V
output transistor, Q1, can no longer operate properly and I
may not be maintained as a constant. As I
voltage required across the transistor, Q1, also decreases and,
therefore, lower supplies can be used with the voice coil motor.
As the current increases to 120 mA through the voice coil,
V
minimum specified compliance voltage of 600 mV (or 480 mV,
if I
components R
coil and the AD5821A is modeled as R
L
maintained as a constant, it is not as critical as the purely resistive
component of the ground return path. When the maximum sink
current is flowing through the motor, the resistive elements, R
R
could, in turn, limit the maximum value of R
voltage compliance.
For example, if
Then the largest value of resistance of the voice coil, R
G
SENSE
G
COIL
, may have an impact on the voltage headroom of Q1 and
SINK
influence R
V
R
R
I
V
R
3.6
SINK
increases. V
is 300 mV, and the minimum drain to source voltage of
G
T
BAT
DROP
= 90 mA). The ground return path is modeled by the
C
= 0.5 Ω
= 0.5 Ω
=
V
= 120 mA
= 3.6 V
V
= 600 mV (compliance voltage)
−
BAT
[600
G
SENSE
and L
−
DROP
[
mV
V
and R
DROP
120
G
decreases and eventually approaches the
SINK
+
. The trace resistance between the voice
2
+
C
mA
×
may not be maintained as a constant.
equally, and because the current is
(
(120
I
SINK
I
SENSE
SINK
mA
×
is 400 mV, and the minimum
R
DROP
T
×
)
0.5
+
T
falls below 480 mV, the
. The inductive effects of
(
I
SINK
Ω)]
SINK
C
decreases, the
×
=
because of
R
24
G
)]
Ω
=
C
, is
DROP
SINK
T
and
Rev. 0 | Page 13 of 16
Using another example, if
Then the largest value of resistance of the voice coil, R
For this reason, it is important to minimize any series impedance
on both the ground return path and interconnect between the
AD5821A and the motor. It is also important to note that for
lower values of I
also decreases. This decrease allows the user to either use voice
coil motors with high resistance values or decrease the power
supply voltage on the voice coil motor. The compliance voltage
decreases as the I
The power supply of the AD5821A, or the regulator used to supply
the AD5821A, should be decoupled. Best practice power supply
decoupling recommends that the power supply be decoupled
with a 10 μF capacitor. Ideally, this 10 μF capacitor should be of
a tantalum bead type. However, if the power supply or regulator
supply is well regulated and clean, such decoupling may not be
required. The AD5821A should be decoupled locally with a
0.1 μF ceramic capacitor, and this 0.1 μF capacitor should be
located as close as possible to the V
should be ceramic with a low effective series resistance and
effective series inductance. The 0.1 μF capacitor provides a low
impedance path to ground for high transient currents.
The power supply line should have as large a trace as possible to
provide a low impedance path and reduce glitch effects on the
supply line. Clocks and other fast switching digital signals should
be shielded from other parts of the board by digital ground.
Avoid crossover of digital and analog signals, if possible. When
traces cross on opposite sides of the board, they should run at
right angles to each other to reduce feedthrough effects through
the board. The best technique is to use a multilayer board with
ground and power planes, where the component side of the
board is dedicated to the ground plane only and the signal
traces are placed on the solder side. However, this is not always
possible with a 2-layer board.
V
R
R
I
V
R
3.6
SINK
G
T
BAT
DROP
C
= 0.5 Ω
= 0.5 Ω
=
V
= 90 mA
= 3.6 V
= 480 mV (compliance voltage specification at 90 mA)
V
−
BAT
[480
−
SINK
SINK
[
mV
V
DROP
the compliance voltage of the output stage
current decreases.
90
+
2
+
mA
×
(
I
SINK
(90
I
SINK
×
mA
R
DD
T
)
×
pin. The 0.1 μF capacitor
+
0.5
(
I
SINK
Ω)]
×
=
33.66
R
G
AD5821A
)]
=
Ω
C
, is