AD5737 Analog Devices, AD5737 Datasheet - Page 37

• Manufacturer Part Number: AD5737
• Description: Quad Channel, 12-Bit, Serial Input, 4-20mA Output DAC with Dynamic Power Control and HART Connectivity
• Manufacturer: Analog Devices

Specifications of AD5737

• Resolution (bits): 12bit
• Dac Settling Time: 15µs
• Max Pos Supply (v): +33V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: Ser,SPI

Data Sheet
AI
The AI
static operation because the output power increases to charge
the output capacitance of the dc-to-dc converter. This transient
current can be quite large (see Figure 57), although the methods
described in the Reducing AI
can reduce the requirements on the AV
If not enough AI
drops. Due to this AV
slewing increases further, causing the voltage at AV
further (see Equation 3). In this case, the V
therefore, the output voltage, may never reach their intended
values. Because the AV
this voltage drop may also affect other channels.
Reducing AI
Two main methods can be used to reduce the AI
requirements. One method is to add an external compensation
resistor, and the other is to use slew rate control. These methods
can be used together.
CC
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Figure 57. AI
0
SUPPLY REQUIREMENTS—SLEWING
0
CC
current requirement while slewing is greater than in
CC
CC
0.5
Current Requirements
CC
Current vs. Time for 24 mA Step Through 1 kΩ Load
with Internal Compensation Resistor
AI
I
V
OUT
BOOST
current can be provided, the AV
CC
CC
CC
drop, the AI
1.0
voltage is common to all channels,
INDUCTOR = 10µH (XAL4040-103)
TIME (ms)
CC
Current Requirements section
1.5
0mA TO 24mA RANGE
CC
current required for
CC
supply.
f
SW
BOOST_x
2.0
1kΩ LOAD
T
= 410kHz
A
= 25°C
CC
voltage and,
current
CC
CC
2.5
to drop
voltage
30
25
20
15
10
5
0
Rev. A | Page 37 of 44
Adding an External Compensation Resistor
A compensation resistor can be placed at the COMP
in series with the 10 nF compensation capacitor. A 51 kΩ exter-
nal compensation resistor is recommended. This compensation
increases the slew time of the current output but reduces the AI
transient current requirements. Figure 58 shows a plot of AI
current for a 24 mA step through a 1 kΩ load when using a 51 kΩ
compensation resistor. The compensation resistor reduces the
current requirements through smaller loads even further, as
shown in Figure 59.
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Figure 59. AI
Figure 58. AI
0
0
0
0
0mA TO 24mA RANGE
1kΩ LOAD
f
INDUCTOR = 10µH (XAL4040-103)
T
SW
A
= 25°C
= 410kHz
with External 51 kΩ Compensation Resistor
with External 51 kΩ Compensation Resistor
AI
I
V
CC
OUT
CC
0.5
0.5
BOOST
CC
Current vs. Time for 24 mA Step Through 500 Ω Load
Current vs. Time for 24 mA Step Through 1 kΩ Load
1.0
1.0
TIME (ms)
TIME (ms)
AI
I
V
INDUCTOR = 10µH (XAL4040-103)
OUT
BOOST
CC
1.5
1.5
0mA TO 24mA RANGE
f
SW
2.0
2.0
500Ω LOAD
T
= 410kHz
A
= 25°C
AD5737
DCDC_x
2.5
2.5
32
28
24
20
16
12
8
32
28
24
20
16
12
8
4
0
4
0
pin
CC
CC