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# Ltc2439-1 in SPI communication data output is high first out or low first out?

Read data is 0XF4,0X53,0XFE, how to parse?

help
[edited by: ljln119 at 3:25 AM (GMT 0) on 14 Jan 2020]
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• I'm not sure what you mean by how to convert the voltage value.

• For example, the 24-bit read value is 00123456 hexadecimal, how to convert to the actual value of the voltage?

• If you look at Table 1 of the data sheet you will see that if the first 4 bits of the output word are 0s, that indicates that the input voltage is below -Full Scale (-0.5*Vref). Let me pick a value that is not railed for an example. 20111111 hexadecimal. According to Table 1, if the first 4 bits are a Hex 2 (0010) then Vin is between 0V and 0.5*Vref. Bits 28 to 5 are the 24-bit conversion result MSB first. Bits 4 to 0 are sub LSBs that can be included if desired or ignored. For simplicity I will ignore the sub LSBs. This results in a 24-bit output code of 008888 hex. Converting that to decimal produces 34952. Dividing that by 2^24 yields 0.0020833015. Multiplying that by the reference voltage (5V) will produce the input voltage, in this case 0.0104165077V.

• Thank you for your reply!Another question is, how to convert the GPIO voltage read by ltc6811-2 chip to the actual voltage value?

VREF2 Is the 34-pin output voltage of ltc6811-2。T1~T5 is connected to the MCU, JT1 is the connector, connected to the temperature probe, measuring temperature range is -55~100℃，Refer to the development board circuit。

• Waiting for your reply, thank you！

• That question should be asked in the Energy Monitoring and Metering Forum.