AD5755-1ACPZ Analog Devices Inc, AD5755-1ACPZ Datasheet - Page 42

• 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

AD5755-1
POWER DISSIPATION CONTROL
The AD5755-1 contains integrated dynamic power control
using a dc-to-dc boost converter circuit, allowing reductions in
power consumption from standard designs when using the part
in current output mode.
In standard current input module designs, the load resistor
values can range from typically 50 Ω to 750 Ω. Output module
systems must source enough voltage to meet the compliance
voltage requirement across the full range of load resistor values.
For example, in a 4 mA to 20 mA loop when driving 20 mA, a
compliance voltage of >15 V is required. When driving 20 mA
into a 50 Ω load, only 1 V compliance is required.
The AD5755-1 circuitry senses the output voltage and regulates
this voltage to meet compliance requirements plus a small
headroom voltage. The AD5755-1 is capable of driving up to
24 mA through a 1 kΩ load.
DC-TO-DC CONVERTERS
The AD5755-1 contains four independent dc-to-dc converters.
These are used to provide dynamic control of the V
voltage for each channel (see Figure 73). Figure 80 shows the
discreet components needed for the dc-to-dc circuitry, and the
following sections describe component selection and operation
of this circuitry.
Table 34. Recommended DC-to-DC Components
Symbol
L
C
D
It is recommended to place a 10 Ω, 100 nF low-pass RC filter
after C
reduces the amount of ripple on the V
DC-to-DC Converter Operation
The on-board dc-to-dc converters use a constant frequency,
peak current mode control scheme to step up an AV
4.5 V to 5.5 V to drive the AD5755-1 output channel. These are
designed to operate in discontinuous conduction mode (DCM)
with a duty cycle of <90% typical. Discontinuous conduction
mode refers to a mode of operation where the inductor current
goes to zero for an appreciable percentage of the switching
cycle. The dc-to-dc converters are nonsynchronous; that is, they
require an external Schottky diode.
DC-to-DC Converter Output Voltage
When a channel current output is enabled, the converter regulates
the V
whichever is greater (see Figure 53 for a plot of headroom
supplied vs. output current). In voltage output mode with the
DCDC
DCDC
DCDC
BOOST_x
AV
DCDC
CC
≥10µF
Component
XAL4040-103
GRM32ER71H475KA88L
PMEG3010BEA
. This consumes a small amount of power but
C
supply to 7.4 V (±5%) or (I
IN
L
10µH
DCDC
Figure 80. DC-to-DC Circuit
SWx
D
C
4.7µF
DCDC
DCDC
R
OUT
FILTER
BOOST_x
Value
10 μH
4.7 μF
0.38 V
10Ω
× R
LOAD
F
supply.
C
0.1µF
FILTER
+ Headroom),
V
Manufacturer
Coilcraft®
Murata
NXP
BOOST_X
BOOST
CC
input of
supply
Rev. A | Page 42 of 48
output disabled, the converter regulates the V
+15 V (±5%). In current output mode with the output disabled,
the converter regulates the V
Within a channel, the V
V
can be tied together.
DC-to-DC Converter Settling Time
When in current output mode, the settling time for a step greater
than ~1 V (I
dc-to-dc converter. The exception to this is when the required
voltage at the I
7.4 V (±5%). A typical plot of the output settling time can be
found in Figure 49. This plot is for a 1 kΩ load. The settling time
for smaller loads is faster. The settling time for current steps less
than 24 mA is also faster.
DC-to-DC Converter V
The maximum V
register (23 V, 24.5 V, 27 V, or 29.5 V; see Table 25). On reaching
this maximum voltage, the dc-to-dc converter is disabled, and
the V
V
is reenabled, and the voltage ramps up again to V
required. This operation is shown in Figure 81.
As can be seen in Figure 81, the DC-DCx bit in the status register
asserts when the AD5755-1 is ramping to the V
deasserts when the voltage is decaying to V
DC-to-DC Converter On-Board Switch
The AD5755-1 contains a 0.425 Ω internal switch. The switch
current is monitored on a pulse by pulse basis and is limited to
0.8 A peak current.
DC-to-DC Converter Switching Frequency and Phase
The AD5755-1 dc-to-dc converter switching frequency can be
selected from the dc-to-dc control register. The phasing of the
channels can also be adjusted so that the dc-to-dc converter can
clock on different edges (see Table 25). For typical applications,
a 410 kHz frequency is recommended. At light loads (low output
BOOST_x
BOOST_x
BOOST_x
29.6
29.5
29.4
29.3
29.2
29.1
29.0
28.9
28.8
28.7
28.6
supply so that the outputs of the I
voltage has decayed by ~0.4 V, the dc-to-dc converter
0
OUT
voltage is allowed to decay by ~0.4 V. After the
V
DC_DC BIT
DC-DCx BIT = 1
DC-DCx BIT = 0
OUT_x
MAX
× R
0.5
Figure 81. Operation on Reaching V
BOOST_x
LOAD
pin plus the compliance voltage is below
1.0
) is dominated by the settling time of the
OUT_x
voltage is set in the dc-to-dc control
MAX
1.5
Functionality
BOOST_x
and I
TIME (ms)
0mA TO 24mA RANGE, 24mA OUTPUT
OUTPUT UNLOADED
DC-DCMaxV = 11 (29.5V)
f
T
2.0
OUT_x
SW
A
supply to 7.4 V (±5%).
= 25°C
= 410kHz
stages share a common
2.5
OUT_x
MAX
BOOST_x
3.0
MAX
and V
− ~0.4 V.
MAX
MAX
value but
3.5
supply to
, if still
OUT_x
4.0
stages