Broad Reach I/O BoardI don't know much about this board's function besides that it's made by Broad Reach, and the latest date codes I can see are from 2009 (with some going back to 2002). Broad Reach,
now part of Moog (no, not the synthesizer company), seems to make general-purpose spacecraft & satellite electronics.
This looks like an I/O board, judging by what's on it - the blue connector at one end looks like it goes to a common backplane, while the small D-sub connector at the other end seems like external I/O.
The board isn't conformal coated, but with a lot of tightly-packed components and most of the traces being internal, there's a limit to how much I was willing to figure out with continuity checks alone. So sticking to a sanity-retaining number of strategically-placed continuity checking and applying a lot of educated guessing, this is my best guess at how things are connected.
Unlabeled ICs are all
Linear Technology RH1014 quad op-amps, except the gold package which is an
Intersil OP470 quad op-amp.
1. Power Supply: An isolated power supply, based on the classic UCx845 PWM controller series, creates the logic & analog supply voltages. Input is probably from a 28VDC bus. The metal box on the bottom side is the primary-side power MOSFET. The vertical cylinder is the bobbin & core of a flyback inductor. An
ST RHFL4913 LDO on the bottom side probably provides a low FPGA core voltage or something like that.
2. Analog Outputs: 2x identical channels, each with an NPN Darlington & PNP Darlington pair for some class-B analog-output action; all in metal cans. NPNs are 2N5667, PNPs are 2N5416. Diodes on the bottom offset the NPN & PNP bases (with a substantial voltage gap for no idle current), and the 5th metal-can transistor per channel creates a current source for biasing. Because of the inherent inaccuracy of a straight class-B emitter-follower, esp. with the large NPN/PNP conduction gap, I assume some of the op-amps wrap feedback loops around these. There's current limiting and common biasing involving some smaller SMT transistors.
3. Push-Pull Digital Outputs: 3x identical channels, each with an IRHNM57110 N-MOSFET & IRHNM597110 P-MOSFET with their drains connected to each other, and to an output pin. Outputs are clamped to ground & supply by diodes on the bottom and top. Gate drive & level-shifting seems to be done by small transistors on top side. The last un-paired P-MOSFET at one end gates the positive supply voltage to all the channels' P-FETs, as a global power enable.
4. Open-Drain Digital Outputs: 2x identical channels, each with an IRHNM57110 N-MOSFET on the bottom side (with its drain connected to an I/O pin) and gate drive circuitry on the top side.
5. Current Sense: 6x separate current sense channels, with Kelvin-connected current sense resistors & op-amps to differential-amplify the current sense voltages; these seem to measure the current draw on various supply voltages, probably ones that get used for driving outputs to monitor total output current. These connect to analog mux inputs (discussed next) and so these current draw readings are probably read by the ADCs along with all the other analog input values.
6 & 7. Mystery: I have no idea what these do. #6 has 2 NPN power transistors on the bottom, with 7 smaller transistors on the top. #7 has a single NPN power transistor & 2 optoisolators, the
Mii 66183. The top-side 2N5339 only has connections to the input-power bus and has a zener to its base, so may be for something like fast discharge on power-down, or crowbarring the power supply's input voltage.
The FPGA, an Actel part, likely provides an interface between a processor bus from a controller card elsewhere, and all the peripherals here.
Besides the digital outputs and various controls, the main peripherals here are 3 DACs (the 12-bit
Analog Devices AD667S) and 3 ADCs (the 16-bit Maxwell, now DDC,
7809LP).
DACs: 2 of these likely create the setpoints for the analog output drivers (#2 in the list above). The 3rd may drive a general-purpose low-power analog output.
ADCs: 3x
Analog Devices MUX-16 16:1 muxes seem to feed up to 48 analog channels to the ADCs, such as this one on the bottom side with a thermistor attached to it:
Some of the muxed ADC channels are definitely used for power-supply current sensing (#5 in the list above), and the rest are probably for general-purpose analog inputs from the outside world.
Reference voltage: The "pattern-breaking" metal can near the analog outputs is a
Linear Technology LT1021 5V voltage reference; I'm guessing this creates a common reference voltage for the ADCs & DACs.
The ADCs themselves are the ones in the interesting extra-thick packages:
From reading the 7809LP datasheet, it looks like the radiation-induced latchup protection is implemented by using a commercial ADC die, with a rad-hard power control circuit wrapped around it to detect fault conditions and cycle its power. I considered opening one of the packages to see this hybrid construction inside, but decided to read up on the Rad-Pak packaging first,
covered by US Patent # 6455864, and realized it would probably be full of goop and therefore not worth it. The core of the Rad-Pak shielding method, if I'm reading the patent correctly, is a conformal coating consisting of tungsten particles held together by an adhesive binder. The high density of tungsten helps block ionizing radiation, similar to lead shielding used with nuclear reactors, medical X-rays, etc.
Here's some better close-up views of...
The power supply:
...including the stack of ceramic caps, given a lead frame to trade vertical space for horizontal space, and to avoid some cracking issues created by mismatched thermal expansion between the ceramic & the PCB material. The ADCs have some pretty large SMT ceramic caps too, but not quite as large (horizontally) as these.
The external-I/O connector:
...with a metal-can LM117 adjustable regulator next to it (I haven't figured out where the LM117's output voltage goes to: not to the I/O connector)
Current-sense circuitry, where you can see the Kelvin-sense terminals on the series resistors:
The LDO:
Misc. things on the bottom side:
You can see the impressive amount and quality of reworks applied, in some of these photos, which makes me wonder if this was a prototype of some kind. There was also an impressive amount of polyimide tape applied to every single wire and "floating" component, to hold them all securely in place - I removed most of the tape though to see the board (& reworks) better.
Anyways, hope this was interesting - wish I could provide a schematic for this one.