Transcript design_review - ECE Senior Design

Current Monitor
Group (1606)
Maya Dubrow
Barath Parthasarathy
Andrew Pikul
Jason Stock
Outline
Executive Summary
System Breakdown
Characterization and Data
Executive Summary:
Timeline
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.
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
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
Ranging Circuit
Optoisolators: P227G
Mosfet: BUK 72150
Mux: MAX 7368
Analog 2x 4:1 multiplexer
100 kHz bandwidth
Supply voltage 3.3V
Second Stage Gain
ADG704
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
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.
Antialiasing Filter
●
Approached the problem in a few different manners
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LTC1564
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Digitally controlled antialiasing filter
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Adjustable cutoff frequency from 10kHz to 150kHz in steps of 10kHz
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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.
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MAX274
○
8th order continuous time filter
○
Can be configured in bessel, butterworth, and chebyshev models
TI’s Webench
Ended up designing a 5th-order bessel filter from scratch using TI’s Webench
software.
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 +/- 2.375V 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
LTC1065 Schematic & Tables
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
2.5-5.5V operating voltage
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)
DAQ (USB → Computer)
Company Device
8 analog in (or 4 differential) fs = (48 kHz / #channels)
16 GPIO (Software Polled)
Software
.NET Driver (VB Requested)
Can do a voltage sweep with the DC Supply
Collects Data and Displays
Exports to Excel
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.
Analysis
Analysis
Analysis
Analysis
Power Circuits
Sense amplifier is self powered!
3.3 Volts for IC
24 Volts for 2nd Stage Gain (Post Processing)
Gate Driver
Voltage Regulator
Required to power extra components to precise voltages ( Mux, Anti-aliasing, optoisolators, 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
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