Space
Shrinking communication satellite subsystems
There are more than 20,000 satellites in orbit, serving both military and commercial customers. Their missions span a wide range of functions including reconnaissance, surveillance, meteorology, navigation, television, and voice communications. With every new mission, customers increasingly want more functionality, which requires larger satellite payloads, forcing manufacturers to increase the size, weight and power of their satellite subsystems. Allan Robinson, a lead applications engineer in Renesas’ Intersil Space/Hi-Rel Division, Renesas Electronics discusses how teaming the ISL72813SEH 32-channel driver IC with a 32-channel multiplexer can overcome satellite payload challenges by shrinking the size of command and telemetry subsystems by up to 50 per cent. He will also discuss the basic operation of the command output circuit, and its role in the overall telemetry system
F
igure 1 shows a block diagram for a next-generation satellite command and telemetry subsystem that typically has hundreds of telemetry inputs and command outputs. The 32-channel driver array controls the relays and solenoids used to turn on and off the propulsion system thrusters, to change orbital altitude, configure payload waveguide and coax switches, or turn on a motor to tilt the solar panels.
The ISL72813SEH 32-channel driver circuit IC drives the coils of relays,
Figure 2: Block diagram of command output circuit
Figure 1: Block diagram of next- generation command and telemetry subsystems
waveguide and coaxial switches that can require up to 500mA of current and -28V across their coils. The logic inputs to the ISL72813SEH are TTL/CMOS compatible allowing easy interface to CPUs, FPGAs, or µProcessors.
Operation of the control command output circuit The circuit in Figure 2 consists of six ISL72813SEH driver ICs that allows for 192 command outputs. Each output goes to the coil of either a relay or a solenoid in a waveguide or coaxial switch that require -28Vdc across their coils to activate their main circuit. A relay coil draws <100mA of current while a waveguide/coaxial solenoid can draw up to 500mA current. The commands from these devices are used
www.cieonline.co.uk
to control the communications payload and other subsystems in the spacecraft. Power for the relay and switch coils is provided by a -30V dc power source connected at the common-emitter (VEE) of the six drivers. The -30V dc source provides up to 500mA to power the ISL72813SEH outputs. An ISL72813SEH device has five logic inputs (A0 – A4) to select one of the 32 driver channels and an enable pin used to disable all of the 32 channels when driven low. Each of the (A0 – A4) logic pins of the six ISL72813SEH drivers are connected in parallel and connected to five of the FPGAs logic outputs. Each enable pin of the six drivers goes to a separate FPGA output logic pin. Only one of 32 channels is activated at a time. However, it is possible to turn on up to six channels simultaneously by driving all six of the enable pins high. When the flight computer
commands a specific driver channel to be activated, the FPGA will apply the appropriate logic signals to select and enable the channel. It then holds the enable pin high for a specific time, which generates a -28V at the output of the selected channel to drive the channel’s load.
The application only requires 12 logic outputs from the FPGA to control the 192 command outputs. The logic inputs of the six ISL72813SEH devices responds to TTL logic levels and the FPGA drives them directly with 3.3V or 5V logic.
Advantages of the 32-channel driver Older designs use discrete current driver arrays to build the command output subsystem. One ISL72813SEH part replaces four discrete current driver array ICs, 32 blocking diodes and 16 level shifting circuits consisting of 48 resistors, 16 transistors, and a pair of decoder ICs that are used to select one of the 16 level shifting circuits. On a circuit card with 192
command outputs, six ISL72813SEH parts would replace 24 discrete driver
Figure 3: ISL72813SEH functional block diagram
array parts, 192 blocking diodes, two 3-to-8 decoders, and 16 level shifting circuits, including 48 resistors and 16 transistors. The new output design offers better than a 2:1 footprint reduction over the old design. Figure 3 shows the ISL72813SEH functional block diagram. It is a radiation hardened 32-channel high- voltage, high current driver circuit with integrated level shifter and 5-bit to 32-bit logic decoder. The decoder selects one of the 32 available driver channels, and its enable pin can disable all 32 channels. The device integrates 32 high current
complementary Darlington drivers that feature high-voltage, common emitter, and open-collector outputs with a 42V breakdown voltage and peak current rating of 600mA.
www.renesas.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
