1. Current Monitor Group (1606)
Maya Dubrow
Barath Parthasarathy
Andrew Pikul
Jason Stock

2. Outline Executive Summary System Breakdown Characterization and Data
Timeline
Executive Summary: We’ve designed a ranging HIGH-SIDE current monitor, which attaches directly to their DC supply. We use a low-resistance sense resistor and amplifier to measure the sense voltage drop. We’ve begun characterization of this circuit on a mix of breadboard and PCB. Printed/No Lead board would mean better components. No one would be impressed, but we could turn in what we have and meet the bare minimum requirements.
The company wants software too.

3. System Breakdown
Sensing Circuit [Group] Built!
Ranging Circuit [Group] Built!
Signal Postprocess
(Analog) [Maya, Jason] Designed
(Digital) [AJ] Done
Microcontroller (Controls All ICs) [AJ] In Design
Power Circuits [Barath] Designed

4. Sensing Circuit Amplifier: LTC6101
Amplifies signal to be used for output.
3 separate op amps are used to reduce error caused by FET impedance. Trimmer’s will be used to correct gain variability.
Resistors from Vishay and Ohmite
Very low thermal coefficients
High power rating

5. Ranging Circuit Optoisolators: P227G Mosfet: BUK 72150 Mux: MAX 7368
Analog 2x 4:1 multiplexer
100 kHz bandwidth
Supply voltage 3.3V

6. Second Stage Gain ADG704 OPA1612 Analog 1x 4:1 multiplexer
Large bandwidth (MHz)
Supply voltage 3.3V
OPA1612
Max supply voltage 36 V
Bandwidth of 40 MHz at G=1
Low input offset voltage and current
Low common mode voltage of +/-2V

7. Aliasing & Anti-Aliasing
Aliasing is a phenomenon of sampled data filters which causes two signals to become indistinguishable from one another due to overlapping
It can occur when a signal is sampled insufficiently
Anti-Aliasing is a common practice using an anti-aliasing filter to limit, or restrict the bandwidth to that of the Nyquist limit.
I think they’ll know what aliasing is (I think), you can demonstrate your knowledge by just explaining why you chose the frequencies you did.

8. Antialiasing Filter Approached the problem in a few different manners
LTC1564
Digitally controlled antialiasing filter
Adjustable cutoff frequency from 10kHz to 150kHz in steps of 10kHz
The sampling frequency for our DAQ is 48kHz, so our cutoff frequency should be roughly 24kHz.
Using this filter would be problematic because we would have to use either 20kHz or 30kHz, so there would be some insufficient sampling rates.
MAX274
8th order continuous time filter
Can be configured in bessel, butterworth, and chebyshev models
Main drawback is that this seemed like a really unorganized design that would cause a lot of confusions during the implementation process.

9. TI’s Webench
Ended up designing a 5th-order bessel filter from scratch using TI’s Webench software.

10. LTC1065
After a bit of research, we ended up finding a 5th order Bessel filter IC.
This helps immensely, and cuts down on implementation time.
LTC1065
Antialiasing filter with linear phase response
Operates from +/ V to +/-8.0V
Closely approximates a 5th order Bessel polynomial
Maximum cutoff frequency of 50kHz (controlled by an internal or external clock)
An input RC circuit can be used to attenuate incoming signals close to the filter clock frequency
Choosing the R value according to Table 1, will keep the Bessel passband response constant
Using an input signal whose frequency is in the range of fCLK +/-6% an alias signal will be generated into the filter’s passband and stopband.
100:1 clock-to-cutoff frequency ratio

11. LTC1065 Schematic & Tables

12. Digital Potentiometer
The LTC1065 will benefit from having a digital potentiometer in place of the input resistance, Rin.
This will allow Phonon to generate different sample rates of the Bessel filter based on a table in the LTC’s datasheet
X9111 Potentiometer
1024 resistance taps
10-bit resolution
Maximum resistance of 100kΩ
V operating voltage
Wiper resistance of 40Ω typical at 5V

13. 𝝻Controller 4 GPIO for 3 multiplexers (range and gain)
4 GPIO for serial to DAQ
3 for possible auto ranging (comparator detection)
3 for SPI to Filter
1 for Clock to Filter
Total: 15 I/O… we can use a ATmega328P!
(power up/power down behavior is very important)

14. DAQ (USB → Computer) Software
Company Device
8 analog in (or 4 differential) fs = (48 kHz / #channels)
16 GPIO (Software Polled)
.NET Driver (VB Requested)
Software
Can do a voltage sweep with the DC Supply
Collects Data and Displays
Exports to Excel

15. Collected Data for 15 ohm DUT
Blue- 0.1Ω Rsense
Red- 0.25Ω Rsense
Green- 0.5Ω Rsense
Data was collected for 6 other DUTs: 49Ω, 100Ω, 200Ω, 500Ω, 1.2kΩ, 2.5kΩ.

16. Analysis

17. Analysis

18. Analysis

19. Analysis

20. Power Circuits Sense amplifier is self powered! 3.3 Volts for IC
24 Volts for 2nd Stage Gain (Post Processing)
Gate Driver

21. Ensure Stability of output voltage
Voltage Regulator
Required to power extra components to precise voltages ( Mux, Anti-aliasing, opto- isolators, amplifier etc.)
LM317 (3.3 V regulator) (2 V dropout)
UM7824 (24 V regulator) (2 V dropout)
This regulator is used specifically for the 2nd stage gain.
P(wasted)=(Vin-Vout)*Iout
The larger the power, the more we need a heat sink.
Ensure Stability of output voltage

22. Gate Driver
LTC1910
Responsible for detecting a current overload within the LTC6101.
The devices turns off in harsh environments.
This time can be adjusted by the capacitance on pin 2 (150,000*C=T(delay))
Example: .33uF resistor gives us 50ms termination