Components Review

Here I give a review of electronic components that I used, particular on their quirks.

Atmega644A
Atmega644A has the same peripherals as Atmega644P, but Atmega644A has the same device signature (1E 96 09) as Atmega644, which is different from Atmega644P (1E 96 0A).  Atmega644 has to be used for device programming with avrdude.  There seems very little difference between Atmega644A and Atmega644PA.

The bootloader based on Atmel app note AVR109 works with avrdude.  Sometimes, the first invocation of avrdude does not work, but the 2nd invocation should work.

By default the clock source is the calibrated internal 8MHz RC clock, and the divide-by-8 bit is enabled, so the system clock is effectively 1MHz.  The JTAGEN is programmed by default, so the side effect is that PORTC2-5 are not I/O ports, DDRC has no control over them.  They have pullups on them.  The JTAGEN fuse should be unprogrammed to enable I/O port for these pins.  The BOOTRST should be programmed to point to the bootloader if used.  The default bootloader size is 4K 16-bit words.  The AVR109 bootloader fits in 1K words.  The 1K bootloader starts at 0xF800.

The I/O port pullup strength is about 38.5K.  The bandgap voltage has some spread, one measured 1.07V and another 1.16V.

The UARTs work at 38400 baud with the internal 8MHz RC clock.  But for reliability the crystal oscillator is still preferred.

The brown-out detection function turns out to be very useful to eliminate bizarre, inexplicable and intermittent behaviors at power on and off.  When the BODLEVEL set to 100, the brownout voltage is 4.3V as specified.

When switching between the ADC channel, ample settling time should be given.

MAX3232
Dual Channel RS232 transceivers output +/-5.4V with 5V supply.

MAX488
RS422 transceiver.

SN74LVC1G86
The single XOR logic gate is in the small SOT23-5 package.  VOL is 0.1V when sinking 12mA with 5V supply.

ADG706
The 16:1 analog mux.

AD8602A
The OpAmp.

LMC6484
This is a general purpose quad CMOS opamp with rail-to-rail I/O.  The maximum voltage is 16V.  The gain-bandwidth product is 1.5MHz.  

AD8210
A current shunt monitor works with common-mode input -2V to 65V at a supply voltage of 5V.  To work below the supply voltage, it uses a pull up on the input, so the common-mode input impedance is only 1.5KOhms.  The side effect is that it injects voltage into the input, which might not desirable.

LMP8602
It is superior to AD8210 in many ways. The bias current is smaller, the quiescent current is lower, the common-mode input range is wider, the specified supply voltage range is wider.  The 50x gain reduces the power dissipation on the sense resistor.  It has a more flexible output structure with accessible node between the two gain stages.  The dynamic response is slower than AD8210.

INA282
This current monitor has switched capacitor input with offset cancellation.  But the performance is not as good as advertised.

ACS713
This is a Hall-effect current sensor.  The main advantage is the very low resistance 1.2mOhms.  But the gain and offset are not as good.  The gain has some more nonlinearity and temperature dependency than the shunt current monitor type.   After running high current through it for a while, the offset would change especially noticeable when the current is reduced back to near zero.  I'm not sure if it is just a temperature effect or some sort of magnetic remanence.

LTC4357
The oring controllers can replace oring diodes.  It tries to servo the FET drop to 30mV; the actual drop will depend on the power FET.  It enables loading sharing.  But unlike diodes, it does consume current, about 2mA, and when two are used to form diode OR, they will consume 4mA which could be significant.

LT1910
The N-FET driver includes a charge pump to generate the gate voltage.  It has over-current protection with a external current sensing resistor.  When it is off, it draws about 2mA current which could be significant for low power operations.

LM317
A classic voltage regulator designed by the legendary Bob Widlar can take a maximum input voltage of 40V and output the maximum current of 1.5A.

The LM317DCYR is the TI clone in SOT-223 with top marking L3, retailed for $0.71 a piece.  The reference voltage is measured at 1.251V.  With two 1% resistors (with good tracking), the output can be set to within 0.5%.  Because the adjust pin sources a small current, the voltage setting resistors should not be too large.  

V7809-500
This switching regulator is a drop in replacement for the popular fixed-voltage regulator LM7809.  The specified maximum input voltage is only 32V.  I took it up to 36V and it still regulated and no damage was done it.  The output contains switching noise at the frequency of 312KHz 30-40mVp-p, which can be reduced by the post linear regulator and ferrite beads.  It can also be configured as an inverting regulator (buck-boost), generating -9V.  It has built-in short protection; I accidentally shorted the output, no harm was done to it.

VYB15W-Q24-S5
The isolated DC/DC converter module outputs 5V/3A.  It has low quiescent current.

UHE-15/2000-Q12-C
The isolated DC/DC converter module outputs 15V/2A.  The no load current seems high and it gets hot without loading.

PS710B
A solid-state relay can handle 5A nicely when the two photo-FETs are paralleled.

IRFR1018
The N-Channel power FET has 8mOhms Rds-on.

SUD50P06-15
The P-Channel power FET has 15mOhms Rds-on.

SUM110P06-07
The P-Channel power FET in the D2PAK(TO-263) package has specified 6.9mOhms Rds-on.  At 12A load, the Vds drop is less than 70mV with Vgs at -13V.  It maintains low Rds even with Vgs at -4V.  The Vgs has maximum range of +/-20V.

BSS138
A N-Channel FET in SOT-23 package has low threshold and low Rds-on.

CPC1117N
This is a solid-state relay that is normally closed with resistance of 5Ohms.  It turns off when 0.23mA current is applied with voltage around 1.13V.  I use it to turn on/off a P-channel power FET; it would have the fast turn-off and slow turn-on feature.

LVK24
The 1W 4-terminal current sense resistor comes in 1% and 0.5% tolerance.  I accidentally pulsed it with a large current (by shorting the output); the resistance is off a little since.

DS2E-ML2-DC24V
This two-coil latching relay has the coil resistances of 1.59K and 1.55K Ohms.  Rated at 24V, one coil actuates at minimum 11V and the other coil at minimum 13V.  It can be used as one-bit nonvolatile memory.

SSL-LX5093BYD
This is a blinking yellow LED.  At about 3V, it draws about 6mA when it is on.  It is sometimes convenient to have a blinking LED without having to add an oscillator, but the blinking frequency is fixed about 1-2Hz and is voltage dependent.

Observations

"An engineer has probably about 8 productive hours in a week. So why do we work 40 hours? Because we don't know when the 8 productive hours kick in."

"You might think it is great to have your hobby as your job, but you would end up hating both your hobby and your job."

"Simulation is like masturbation; it is not good for you if you do too much of it."

"National research laboratories are like welfare for engineers and scientists; without them a lot of engineers and scientists will be out on the streets."

"Why do engineers procrastinate?

1. There are fewer criticisms to the design when the time is short.  A design done earlier draws unnecessary criticisms and suggestions for modifications.
2. A design completed earlier makes the task look too easy.
3. The engineer may be rewarded with another task when he finishes early. "

"Be wary of engineers who talk a great deal.  They usually do very little.  In their mind, talking is equivalent to doing."

"I judge people's competency in electronics by looking at their copies of The Art of Electronics. If the book is well-worn, I can trust this person to do electronics; but if the book looks new, I'd conclude that the person is well versed in electronics. If a person does not have this book on his book shelf within arm's reach, he is not into electronics at all."