AD5755-1ACPZ Analog Devices Inc, AD5755-1ACPZ Datasheet - Page 43

• Manufacturer Part Number: AD5755-1ACPZ
• Description: 16Bit Quad,V/I DAC No Dynamic Power Ctrl
• Manufacturer: Analog Devices Inc
• Series: -r

Specifications of AD5755-1ACPZ

• Input Channel Type: Serial
• Data Interface: 3-Wire, Serial
• Supply Voltage Range - Digital: 2.7V To 5.5V
• Digital Ic Case Style: LFCSP
• No. Of Pins: 64
• Operating Temperature Range: -40°C To +105°C
• Rohs Compliant: Yes
• Resolution (bits): 16bit
• Supply Voltage Range - Analog: 2.7V To 5.5V
• Featured Product: AD5755 / AD5755-1 / AD5757 DACs
• Settling Time: 11µs
• Number Of Bits: 16
• Number Of Converters: 4
• Voltage Supply Source: Analog and Digital, Dual ±
• Power Dissipation (max): -
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 64-VFQFN Exposed Pad, CSP
• Number Of Outputs And Type: 4 Current, 4 Voltage
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

current and small load resistor), the dc-to-dc converter enters a
pulse-skipping mode to minimize switching power dissipation.
DC-to-DC Converter Inductor Selection
For typical 4 mA to 20 mA applications, a 10 μH inductor (such
as the XAL4040-103 from Coilcraft), combined with a switch-
ing frequency of 410 kHz, allows up to 24 mA to be driven into a
load resistance of up to 1 kΩ with an AV
5.5 V. It is important to ensure that the inductor is able to
handle the peak current without saturating, especially at the
maximum ambient temperature. If the inductor enters into
saturation mode, it results in a decrease in efficiency. The
inductance value also drops during saturation and may result in
the dc-to-dc converter circuit not being able to supply the
required output power.
DC-to-DC Converter External Schottky Selection
The AD5755-1 requires an external Schottky for correct
operation. Ensure that the Schottky is rated to handle the
maximum reverse breakdown expected in operation and that
the rectifier maximum junction temperature is not exceeded.
The diode average current is approximately equal to the I
current. Diodes with larger forward voltage drops result in a
decrease in efficiency.
DC-to-DC Converter Compensation Capacitors
As the dc-to-dc converter operates in DCM, the uncompensated
transfer function is essentially a single-pole transfer function.
The pole frequency of the transfer function is determined by
the dc-to-dc converter’s output capacitance, input and output
voltage, and output load. The AD5755-1 uses an external capacitor
in conjunction with an internal 150 kΩ resistor to compensate
the regulator loop. Alternatively, an external compensation resistor
can be used in series with the compensation capacitor, by setting
the DC-DC Comp bit in the dc-to-dc control register. In this case,
a ~50 kΩ resistor is recommended. A description of the advantages
of this can be found in the AI
section. For typical applications, a 10 nF dc-to-dc compensation
capacitor is recommended.
DC-to-DC Converter Input and Output Capacitor
Selection
The output capacitor affects ripple voltage of the dc-to-dc
converter and indirectly limits the maximum slew rate at which
the channel output current can rise. The ripple voltage is caused
by a combination of the capacitance and equivalent series
resistance (ESR) of the capacitor. For the AD5755-1, a ceramic
capacitor of 4.7 μF is recommended for typical applications.
Larger capacitors or paralleled capacitors improve the ripple at
the expense of reduced slew rate. Larger capacitors also impact
the AV
AI
at the output of the dc-to-dc converter should be >3 μF under
all operating conditions.
The input capacitor provides much of the dynamic current
required for the dc-to-dc converter and should be a low ESR
CC
Supply Requirements—Slewing section). This capacitance
CC
supplies current requirements while slewing (see the
CC
Supply Requirements—Slewing
CC
supply of 4.5 V to
LOAD
Rev. A | Page 43 of 48
component. For the AD5755-1, a low ESR tantalum or ceramic
capacitor of 10 μF is recommended for typical applications.
Ceramic capacitors must be chosen carefully because they can
exhibit a large sensitivity to dc bias voltages and temperature.
X5R or X7R dielectrics are preferred because these capacitors
remain stable over wider operating voltage and temperature
ranges. Care must be taken if selecting a tantalum capacitor to
ensure a low ESR value.
AI
The dc-to-dc converter is designed to supply a V
See Figure 53 for a plot of headroom supplied vs. output
voltage. This means that, for a fixed load and output voltage,
the dc-to-dc converter output current can be calculated by
the following formula:
where:
I
η
and Figure 56).
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 82), although the methods
described in the Reducing AI
can reduce the requirements on the AV
AI
this AV
further. This means that the voltage at AV
Equation 3) and the V
may never reach its intended value. Because this AV
common to all channels, this may also affect other channels.
OUT
V
BOOST
CC
CC
CC
is the output current from I
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
V
current can be provided, the AV
SUPPLY REQUIREMENTS—STATIC
AI
SUPPLY REQUIREMENTS—SLEWING
0
BOOST
CC
0
is the efficiency at V
CC
CC
current requirement while slewing is greater than in
drop, the AI
Figure 82. AI
=
= I
Efficiency
OUT
0.5
Power
× R
AI
I
V
Internal Compensation Resistor
OUT
BOOST
CC
BOOST_x
CC
LOAD
CC
Current vs. Time for 24 mA Slew with
×
Out
current required to slew increases
AV
1.0
+ Headroom
voltage, and thus the output voltage,
INDUCTOR = 10µH (XAL4040-103)
TIME (ms)
BOOST_x
CC
CC
=
OUT_x
Current Requirements section
η
as a fraction (see Figure 55
I
1.5
V
OUT
0mA TO 24mA RANGE
BOOST
in amps.
CC
CC
×
voltage drops. Due to
V
×
supply. If not enough
CC
f
BOOST
AV
SW
drops further (see
2.0
1kΩ LOAD
T
= 410kHz
BOOST_x
CC
A
= 25°C
AD5755-1
CC
voltage of
2.5
voltage is
30
25
20
15
10
5
0
(2)
(3)