STI EVAL-RHFAD128V2 User manual

Introduction
The EVAL-RHFAD128V2 evaluation board allows evaluating the conversion performance of the RHFAD128 eight-channel
analog-to-digital converter, which is designed for 50 ksps to 1 Msps conversion.
The board can accept external signals to measure and evaluate the RHFAD128 conversion performance, based on its
successive approximation register (SAR) with an internal track-and-hold cell.
The board can be supplied in standalone mode. It can also be connected to a NUCLEO-L476RG development board hosting an
STM32 microcontroller, which enables further signal processing and PC communication.
To monitor the EVAL-RHFAD128V2 performance, when connected to the NUCLEO-L476RG, the RHFAD128_GUI can be used.
Figure 1. EVAL-RHFAD128V2 evaluation board
Getting started with the EVAL-RHFAD128V2 evaluation board for the RHFAD128
analog-to-digital converter
UM3160
User manual
UM3160 - Rev 1 - May 2023
For further information contact your local STMicroelectronics sales office. www.st.com

1Getting started
1.1 Features
• RHFAD128 (Rad-hard, 12-bit 1 MHz A-to-D converter)
• Six direct inputs to the RHFAD128 with RC filters (200 Ω / 10 nF)
• Footprint available for external reference with the RHF100 (1) (Rad-hard 1.2 V fixed Vref)
• Footprint available for single op amp RHF43B (2) for current-sensing and custom test
• 2-layer FR4 printed circuit board
• Single ground-layer that proved the best performance
• Decoupling capacitive network close to the ICs to prevent noise on power supplies
• Connectors on the power supplies and on the output for easy plug-in
• Standard SPI communication pinout
• Numerous test-points
1. The RHF100 is not mounted on the EVAL-RHFAD128V2. However, the footprint is available on the board.
2. The RHF43B is not mounted on the EVAL-RHFAD128V2. However, the footprint is available on the board.
1.2 Main components
1.2.1 RHFAD128
The RHFAD128 is a low-power, eight-channel CMOS 12-bit analog-to-digital converter for conversion from 50
ksps to 1 Msps.
The architecture is based on a successive-approximation register with an internal track-and-hold cell.
The RHFAD128 features eight single-ended multiplexed inputs. The output serial data is straight binary and is SPI
compatible.
1.2.2 RHF100
The RHF100 is an adjustable voltage reference with the following features:
• Fixed shunt: 1.2 V stable on capacitive load
• High precision ± 0.15 %
• Wide operating current: 40 μA to 12 mA
• 15 ppm/°C overtemperature range (-45 °C to 125 °C)
• 2 ppm/°C variation over 3000 hrs
• 0.02% precision stability over 3000 hrs
• 300 krad high and low dose rate
• ELDRS-free up to 300 krad
• Mounted in a Flat-10 hermetic ceramic package
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Getting started
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1.2.3 RHF43B
The RHF43B operational amplifier offers high precision functioning with low input. Rail-to-rail output.
It has the following features embedded:
• Bandwidth: 8 MHz gain at 16 V
• Low input offset voltage: 100 μV typ.
• Supply current: 2.2 mA typ.
• Operating from 3 to 16 V
• Input bias current: 30 nA typ.
• ESD internal protection ≥ 2 kV
• Latch-up immunity: 200 mA
• ELDRS free up to 300 krad
• SEL immune at 120 MEV.cm2/mg
• Mounted in a Flat-8 hermetic ceramic package
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Main components
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2How to use the board
To use the board, follow the procedure below.
Step 1. Connect the power generators to AVCC and DVCC connectors.
The allowed voltages for AVCC and DVCC are 2.7 to 3.3 V.
Two ways to power the board:
1. AVCC and DVCC are connected separately by 2 different power supplies.
In this case the resistance R03 is disconnected.
2. AVCC and DVCC are connected to the same power supplies.
In this case the resistance R03 is connected.
Figure 2. AVCC and DVCC connectors
Step 2 Connect the SPI section.
Figure 3. SPI connection pins
Step 3. When using the RHFAD128_GUI GUI, refer to the table below for the connection between the EVAL-
RHFAD128V2 SPI pins and the NUCLEO-L476RG pins.
Table 1. Pinout connection between the EVAL-RHFAD128V2 and the NUCLEO-L476RG
NUCLEO-L476RG pin EVAL-RHFAD128V2 SPI pin
PB12 Chip select
PB13 SCLK
PB14 MISO
PB15 MOSI
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How to use the board
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Step 4. Connect your inputs.
Step 4a. IN1, IN2, IN3, IN4, IN6, and IN7: direct inputs with RC filters (for example 200 Ω / 10 nF is a good
combination at FCLK = 500 KHz).
Step 4b. IN0: input connected to the reference voltage RHF100.
Step 4c. IN5: input connected to a rail-to-rail amplifier RHF43B.
Figure 4. Board section for input connection
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How to use the board
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3Communication with the RHFAD128
3.1 Option A: use the STSW-AKI GUI
The EVAL-RHFAD128V2 can be used with the STSW-AKI GUI. To use it, it is necessary to use a Nucleo-64
L476RG.
The RHFAD128_GUI runs on an STM32 Nucleo-64 development board. It communicates with the RHFAD128 of
the EVAL-RHFAD128V2 through the SPI protocol at 125 ksps.
The RHFAD128_GUI allows the user to monitor each channel and plot data on a graph. It is also a tool to save
values measured by the RHFAD128 in a .csv file.
For more information on the RHFAD128_GUI GUI, go to the relevant STMicroelectronics web page.
Figure 5. RHFAD128_GUI: GUI for RHFAD128
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Communication with the RHFAD128
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3.2 Option B: use the EVAL-RHFAD128V2 directly with your test solution
The EVAL-RHFAD128V2 can be plugged directly to your solution.
The SPI communication to access the RHFAD128 registers giving access to the measured values of each
channel is shown in the following tables.
Table 2. Control register bits
Bit # 7 (MSB) 6 5 4 3 2 1 0
Symbol DONTC DONTC ADD2 ADD1 ADD0 DONTC DONTC DONTC
Table 3. Control register bit description
Bit # Symbol Description
7, 6, 2, 1, 0 DONTC Don't care
5 ADD2
These bits determine which input channel is converted, as per4 ADD1
3 ADD0
Table 4. Input channel description
ADD2 ADD1 ADD0 Address value (h) Input channel
0 0 0 00 IN0
0 0 1 08 IN1
0 1 0 10 IN2
0 1 1 18 IN3
1 0 0 20 IN4
1 0 1 28 IN5
1 1 0 30 IN6
1 1 1 38 IN7
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Option B: use the EVAL-RHFAD128V2 directly with your test solution
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4The use of RHF43B and RHF100
4.1 1.2 V reference voltage on channel 0
The RHF100 is not mounted on board.
The RHF100 reference voltage can be measured on the channel IN0.
By default, the R42 value can be 0 Ω. However, R42 = 200 Ω and C42 = 10 nF can be a good combination for
low-pass filter at FCLK = 500 KHz.
The measured output voltage is 1.2 V.
Figure 6. Reference voltage
4.2 Current sensing
The RHF43B is not mounted on board.
The RHF43B op amp can be used for current sensing or for voltage amplification. It is connected to the
RHFAD128 input channel 5 (IN5).
The op amp output voltage Vout must be within the range [0 V, AVCC].
By default, the R27 value can be 0 Ω. However, R27 = 200 Ω and C23=10 nF can be a good combination for
low-pass filter at FCLK = 500 KHz.
Figure 7 is an extract of the power supply management schematic.
There are different ways to power the op amp and to measure the current or the voltage:
1. Power supply @ 5 V
• The reference voltage RHF100 * is powered by Vcc = 5 V
• Vcc+ = 5 V → J33 = 5 V → J35 jumper upper side connected
• Vcc- = GND → J37 jumper lower side connected
• REF floating → J38 not connected → R28, R29, R30 not connected
2. Power supply @ custom Vcc- / Vcc+
• Vcc+ = V+ → J34 = custom → J35 jumper lower side connected
• Vcc- = V- → J34 = custom → J37 jumper upper side connected
• REF custom → J38 = custom → R28, R29 connected
• In practice, REF = AVCC
• R28 = R29 = 2 * R26
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The use of RHF43B and RHF100
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Figure 7. RHF100 and RHF43B power supply setup
Figure 8 is an extract of the board schematic. It shows the different modes to measure the amplifier output
voltage.
4.2.1 Mode 1: Low-side current sensing
An external load could be connected to the connector J22. The current through this load is measured by the
following setup:
• J21 = +5 V if the external load is powered by 5 V
• J21 = is open if the external load is powered by external supply
• J22 = LOAD
• J23 = GND
• J24 = REX
• R25 = R23
• R26 = R24
The RHF43B gain is:
• G = R26 / R25
The measured current through the shunt resistance R21 is:
Case 1: REF voltage is not used:
• R24 = R26
• Vout = I * R21 * Gain
• I = Vout / (Gain * R21)
Case 2: REF voltage is used:
• R24 is not connected
• Vout = REF / 2 + I * R21 * Gain
• I = (Vout - REF/2) / (Gain * R21)
4.2.2 Mode 2: High-side current sensing
The setup is the following:
• J21 = GND
• J22 = LOAD
• J23 = REX
• J24 = +5 V if the external load is powered by 5 V
• J24 = is open if the external load is powered by external supply
• R25 = R23
The RHF43B gain is:
• G = R26 / R25
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Current sensing
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The measured current through the shunt resistance R21 is:
Case 1: REF voltage is not used:
• R24 = R26
• Vout = I * R21 * Gain
• I = Vout / (Gain * R21)
Case 2: REF voltage is used:
• R24 is not connected
• Vout = REF/2 + I * R21 * Gain
• I = (Vout - REF/2) / (Gain * R21)
4.2.3 Mode 3: Custom input voltage
The setup is:
• J21 = GND
• J22 = External VIN
• J23 = REX
• J24 = No use
• R21 = Not connected
• R25 = R23
• R26 = R24
• Gain = R26/R25
• Vout = REF/2 + VIN * Gain
Figure 8. RHF43B current sensing
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Current sensing
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