Device Sensors

The ECM1900 has 4 LTC2991 device sensors onboard that reports various voltage, current, and temperature readings. These sensors communicate through an I2C line connected to the processing system (PS) on the ZYNQ MPSoC. The I2C line is connected to MIO pins 16-17 on the PS and can be controlled from the provided Linux image. You can do so by either using the I2C-Tools package installed on the image or by opening the device file at “/dev/i2c-0”.

You’ll need to read the LTC2991’s datasheet to learn more about the device. A brief description of the important information you’ll find within the datasheet is provided below:

  • Information about the V1-8 pin’s operating modes: Voltage, current, and temperature.
  • Configuration registers to setup the modes for the V1-8 pins.
  • Register map to retrieve the sensor readings.
  • Conversion equations to perform on the RAW sensor readings.

The 7 bit address (not including the R/W bit) for these devices are shown below:

  • First LTC2991 = 0x48
  • Second LTC2991 = 0x49
  • Third LTC2991 = 0x4A
  • Fourth LTC2991 = 0x4B

Below are how the 4 LTC2991 device sensors are connected onboard the ECM1900. Please note that the Rsense resistor we use between the Current Diff Pairs is .005 ohm. You can read about the Rsense resistor’s purpose in current calculations at the LTC2991’s datasheet.

pINnETType
V1+1.8V_SRCCurrent Diff Pair V1-V2
V2+1.8VCurrent Diff Pair V1-V2
V3+1.8VVoltage
V4No ConnectN/A
V5+0.9V_VCCINT_VCUVoltage
V6+0.9V_MGTAVCCVoltage
V7+0.9V_MGTAVCC_SRCCurrent Diff Pair V7-V8
V8+0.9V_MGTAVCCCurrent Diff Pair V7-V8
Vcc+3.3VVoltage
LTC2991 Address = 0x48

pINnETType
V1+1.2V_DDR_SRCCurrent Diff Pair V1-V2
V2+1.2V_DDRCurrent Diff Pair V1-V2
V3+1.2V_DDRVoltage
V4+1.2V_MGTAVTTVoltage
V5+1.2V_MGTAVTT_SRCCurrent Diff Pair V5-V6
V6+1.2V_MGTAVTT Current Diff Pair V5-V6
V7FPGA_DXPRemote Diode Temperature
V8FPGA_DXNRemote Diode Temperature
Vcc+3.3VVoltage
LTC2991 Address = 0x49

pINnETType
V1+3.3V_SRCCurrent Diff Pair V1-V2
V2+3.3VCurrent Diff Pair V1-V2
V3VCCO_28_SRCCurrent Diff Pair V3-V4
V4VCCO_28Current Diff Pair V3-V4
V5VCCO_28Voltage
V6VCCO_67Voltage
V7VCCO_67_SRCCurrent Diff Pair V7-V8
V8VCCO_67Current Diff Pair V7-V8
Vcc+3.3VVoltage
PWMFAN_PWM PWM Output to Fan
LTC2991 Address = 0x4a

pINnETType
V1+5V_SRCCurrent Diff Pair V1-V2
V2+5VCurrent Diff Pair V1-V2
V3VCCO_87_88_SRCCurrent Diff Pair V3-V4
V4VCCO_87_88Current Diff Pair V3-V4
V5VCCO_87_88Voltage
V6VCCO_68Voltage
V7VCCO_68_SRCCurrent Diff Pair V7-V8
V8VCCO_68Current Diff Pair V7-V8
Vcc+5VVoltage
LTC2991 Address = 0x4b