參數(shù)資料
型號(hào)： AD5821D-WAFER
廠商： ANALOG DEVICES INC
元件分類： DAC
英文描述： 120 mA, Current Sinking, 10-Bit, I2C DAC
中文描述： SERIAL INPUT LOADING, 250 us SETTLING TIME, 10-BIT DAC, UUC8
封裝： DIE-8
文件頁(yè)數(shù)： 13/16頁(yè)
文件大?。?/td> 386K
代理商： AD5821D-WAFER
AD5821
When sinking the maximum current of 120 mA, the maximum
voltage drop allowed across R
SENSE
is 400 mV, and the minimum
drain to source voltage of Q1 is 200 mV. This means that the
AD5821 output has a compliance voltage of 600 mV. If V
DROP
falls below 600 mV, the output transistor, Q1, can no longer
operate properly and I
SINK
may not be maintained as a constant.
When sinking 90 mA, the maximum voltage drop allowed
across R
SENSE
is 300 mV, and the minimum drain to source
voltage of Q1 is 180 mV. This means that the AD5821 output
has a compliance voltage of 480 mV If V
DROP
falls below 480 mV
the output transistor, Q1, can no longer operate properly and
I
SINK
may not be maintained as a constant. As I
SINK
decreases, the
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
C
increases. V
DROP
decreases and eventually approaches the
minimum specified compliance voltage of 600 mV (or 480 mV,
if I
SINK
= 90 mA). The ground return path is modeled by the
components R
G
and L
G
. The track resistance between the voice
coil and the AD5821 is modeled as R
T
. The inductive effects of
L
G
influence R
SENSE
and R
C
equally, and because the current is
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
T
and
R
G
, may have an impact on the voltage headroom of Q1 and
could, in turn, limit the maximum value of R
C
because of
voltage compliance.
For example, if
V
BATTERY
= 3.6 V
R
G
= 0.5 Ω
R
T
= 0.5 Ω
I
SINK
= 120 mA
V
DROP
= 600 mV (the compliance voltage)
Rev. 0 | Page 13 of 16
Then the largest value of resistance of the voice coil, R
C
, is
+
=
C
R
=
×
+
×
SINK
G
SINK
T
SINK
I
DROP
V
[
BAT
R
I
R
I
V
)]
(
)
(
Ω
24
mA
120
Ω)]
0.5
mA
(120
2
mV
[600
V
3.6
=
×
×
+
Using another example, if
V
BATTERY
= 3.6 V
R
G
= 0.5 Ω
R
T
= 0.5 Ω
I
SINK
= 90 mA
V
DROP
= 480 mV (the compliance voltage specification at 90 mA)
Then the largest value of resistance of the voice coil, R
C
, is
+
=
C
R
=
×
+
×
SINK
G
SINK
T
SINK
I
DROP
V
[
BAT
R
I
R
I
V
)]
(
)
(
Ω
33.66
mA
90
Ω)]
0.5
mA
(90
2
mV
[480
V
3.6
=
×
×
+
For this reason, it is important to minimize any series impedance
on both the ground return path and interconnect between the
AD5821 and the motor. It is also important to note that for
lower values of I
SINK
, the compliance voltage of the output stage
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
SINK
current decreases.
The power supply of the AD5821, or the regulator used to supply
the AD5821, 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 AD5821 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
DD
pin. The 0.1 μF capacitor 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.
相關(guān)PDF資料
PDF描述
AD5821-WAFER 120 mA, Current Sinking, 10-Bit, I2C DAC
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AD584T Pin Programmable Precision Voltage Reference
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
AD5821-WAFER 制造商:AD 制造商全稱:Analog Devices 功能描述:120 mA, Current Sinking, 10-Bit, I2C DAC
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