EVAL-CN0188-SDPZ Analog Devices Inc, EVAL-CN0188-SDPZ Datasheet - Page 2

• Manufacturer Part Number: EVAL-CN0188-SDPZ
• Description: BOARD, EVAL, FOR CN0188
• Manufacturer: Analog Devices Inc
• Series: -r

Specifications of EVAL-CN0188-SDPZ

• Rohs Compliant: YES
• Svhc: No SVHC (15-Dec-2010)
• Main Purpose: Power Management, Current Monitor
• Embedded: No
• Utilized Ic / Part: ADA4051-2, ADR381, ADUM5402, AD7171
• Primary Attributes: -
• Secondary Attributes: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The measurement result from the
digital code utilizing a simple 2-wire, SPI-compatible serial
interface. The entire circuit operates on a single +3.3 V supply.
Optional galvanic isolation is provided by the
channel isolator. In addition to isolating the output data, the
ADuM5402
the circuit. The
operation unless galvanic isolation is needed.
This combination of parts provides a accurate high voltage
negative rail current sense solution with a small component
count, low cost, and low power. The accuracy of the measure-
ment is primarily determined by resistor tolerances and the
accuracy of the band gap reference, and is typically better than 1%.
CIRCUIT DESCRIPTION
The circuit is designed for a full-scale shunt voltage of 50 mV at
maximum load current I
resistor is R
The "ground" for the op amp stage is connected to the
common–mode source voltage (−48 V). The voltage for the op
amp stage is supplied by the "floating" 5.6 V zener diode, which
is biased at a current of approximately 2 mA. This eliminates
the need for a separate power supply. The circuit will operate
with a source voltage from −60 V to −10 V with no
modifications.
The shunt voltage is amplified by a factor of 49.7 using U1A,
where G = 1 + R3/R2. The zero-drift
offset voltage (15 µV maximum) and does not contribute
significant error to the measurement. A full-scale shunt voltage
of 50 mV produces a full-scale output voltage from U1A of
2.485 V (referenced to the common-mode source voltage).
An N-channel MOSFET transistor with a large V
(70 V) inside the feedback loop of U1B applies the output
voltage of U1A across resistor R5, and the resulting current
flows through R6 and R7. The full-scale voltage from U1A of
2.485 V produces a full-scale current of 0.498 mA, which
generates a full-scale voltage of 2.485 V across resistor R7. The
voltage across R7 is applied to AIN− of the ADC. Resistor R6
and the Schottky diode D2 provide input protection for the
AD7171
Notice that the power supply voltage for the ADR381, the
AD7171, and the floating zener diode is supplied by the isolated
power output (+3.3 V
The reference voltage for the
ADR381
initial accuracy of ±0.24% and a typical temperature coefficient
of 5 ppm/°C.
Although it is possible to operate both the
REFIN(+) from the 3.3 V power supply, using a separate
CN-0188
in the event the MOSFET shorts out.
precision band gap reference. The
SHUNT
digital isolator can also supply isolated +3.3 V for
ADuM5402
= (50 mV)/(I
ISO
) of the
MAX
. Therefore, the value of the shunt
is not required for normal circuit
AD7171
MAX
ADuM5402
).
AD7171
ADA4051-2
is supplied by the
AD7171
is provided as a
ADR381
quad isolator.
ADuM5402
DS
has a low
breakdown
VDD and
has an
quad
Rev. A | Page 2 of 5
reference provides better accuracy. A 2.5 V reference is chosen
to provide sufficient headroom.
The input voltage to the
offset binary code at the output of the ADC. The ADuM5402
provides the isolation for the DOUT data output, the SCLK
input, and the PDRST input.
The code is processed in the PC by using the SDP hardware
board and LabVIEW software.
The graph in Figure 2 shows how the circuit tested achieves an
error of 0.3% over the entire input voltage range (0 mV to 50 mV).
A comparison is made between the code seen at the output of
the ADC, recorded by LabVIEW, and an ideal code calculated
based on a perfect system.
In order to calculate this ideal code, there are several
assumptions which must be made about the performance of the
system. First, the op amp gain stage must multiply the input
signal by exactly 49.7. Depending on resistor tolerances (1%),
this value will vary by 2% worst case. Secondly, the current sink
resistor (R5) and the ADC input resistor (R7) are assumed to be
identical. In the circuit, these particular resistors have a
tolerance of 1%. Since they are the same value, the matching
will probably be better than 1%. Resistors with tighter
tolerances can be used, which will increase the accuracy and
the cost of the circuit.
Several items have been implemented on the PCB, which are
not crucial to the function or performance of the circuit but are
required to ensure user and hardware safety. As an example, if
Q1 breaks down or shorts out, the ADC, SDP board, user, and
user’s PC are all at risk due to the large negative voltage
potential. The safety items included are passive elements R6,
D2, which protect the AD7171, and the
channel digital isolator, which protects the circuits on the SDP
board, as well as the user's PC.
65536
62768
57768
52768
47768
42768
37768
32768
0
Figure 2. Plot of Output and Error vs. Shunt Voltage
5
ADC CODE
10
15
SHUNT VOLTAGE (mV)
AD7171
20
25
ADC is converted into an
30
INPUT OUTPUT
35
ADuM5402
ERROR (%)
40
Circuit Note
45
quad-
50
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0