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Part Number: UCD90320

Hi,

Good Day. I have a customer who is working with UCD90320. Please see below his query for your reference. Thank you very much.

READ_TEMPERATURE_1 register is a 16-bit register, what do I do with the value of the computer temperature of the device?

The device documentation describes how to use READ_TEMPERATURE_2 but not READ_TEMPERATURE_1.

Note that my major problem is that someone wrote code to display the temperature but the temperature displayed is colder than ambient. So this should not be possible and I need to manually check the code that is reading this register.

Best Regards,

Ray Vincent

• Hi

The interpretation is the same for READ_1 and READ_2.

Please be noted that READ_1 returns internal temp which has some variations defined in the data sheet.

Regards

Yihe

• Hi Yihe,

Good Day. Please see below the response of our customer to your reply. Thank you very much.

Please provide a working example of this method because when I use it the temperature is 5 degC when I think it should be near 50C (the current SW code that displays this temperature says the temp is 30C).

Both values are wrong, and I am trying to understand where the error is.

Best Regards,

Ray Vincent

• Hi

Regards

Yihe

• Hi Yihe,

Good Day. Please see the latest response from our customer. Thank you very much.

Please provide a working example of this method because when I use it the temperature is 5 degC when I think it should be near 50C (the current SW code that displays this temperature says the temp is 30C).

Both values are wrong, and I am trying to understand where the error is.”

The document:

If the user understands how to make a current reading, then the user should have no problem learning how

to make a temperature measurement reading. The command used for reading a temperature associated

with a given rail is READ_TEMPERATURE_2 (0x8E). The calculated temperature measurement is in units

of °C. The temperature is calculated as Temperature = T × 2X; in which T is the 11-bit signed two's

complement integer obtained from the 11 least significant bits of READ_TEMPERATURE_2 and X is the

5-bit signed two's complement integer obtained from the 5 most significant bits of

• Select the Rail: The PAGE command is set just as it was done with voltage and current measurement

Read the T value and the exponent: The READ_TEMPERATURE_2 (0x8E) is a two-byte command

that contains the exponent (X) and the T value for the equation Temperature = T × 2X.

[St] [AddrW] [A] [W:x8E] [A] [Sr] [AddrR] [A] [R:Data_1] [A] [R:Data_2] [N] [Sp]

Let's assume that the data read back was Data_1 = 0xDB and Data_2 = 0x21. Breaking down to the

11 least significant bits you get that T = 801 decimal. The 5 most significant bits give you 27 decimals

and its two's complement leads to an exponent of -5.

• Calculate the Temperature Measurement: Now we have all the data necessary to calculate the

measured temperature.

Solving the equation Temperature = T × 2X

Temperature = 801 × 2-5 = 25.03°C”

Show the binary value read from the register.

0xdb21

b1101 1011 0010 0001

Show the 11-bit value and the converted “801” two complement values.

B01100100001

Two’s complement: ??

Show the 5-bit value and the converted “-5” two complement values.

B11011

Two’s complement: ??

Using the converted values, show all the math.

Indicate which register values get converted, and which values do not.

I have coded something that appears to work but the method does not align with the TI documentation.

Best Regards,

Ray Vincent

• Hi

The example listed in the document

0xdb21 -> 1101 1011 0010 0001b

The MSB 5 bits is signed exponent 11011b. the MSB 1, so it is a negative number, its twos-complement is 00101 = -5

The LSB 11 bits is 011 0010 0001b so it is positive number = 0x321=801.

The final value is 801*2^-5 = 25C.

Hope he can understand all these.

Regards

Yihe

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