HTU20D Datasheet, PDF (16/23 Pages) TE Connectivity Ltd – Instantaneous desaturation after long periods in saturation phase

HTU20D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
Since the left most divisor bit zeroed every input bit it touched, when this process ends the only bits in the input row
that can be nonzero are the n bits at the right-hand end of the row. These n bits are the remainder of the division
step, and will also be the value of the CRC function.
The validity of a received message can easily be verified by performing the above calculation again, this time with
the check value added instead of zeroes. The remainder should equal zero if there are no detectable errors.
CRC examples
The input message 11011100 (0xDC) will have as result 01111001 (0x79).
The input message 01101000 00111010 (0x683A: 24.7°C) will have as result 01111100 (0x7C).
The input message 01001110 10000101 (0x4E85: 32.3%RH) will have as result 01101011 (0x6B).
CONVERSION OF SIGNAL OUTPUTS
Default resolution is set to 12-bit relative humidity and 14-bit temperature readings. Measured data are transferred
in two byte packages, i.e. in frames of 8-bit length where the most significant bit (MSB) is transferred first (left
aligned). Each byte is followed by an acknowledge bit. The two status bits, the last bits of LSB, must be set to ‘0’
before calculating physical values.
To accommodate/adapt any process variation (nominal capacitance value of the humidity die), tolerances of the
sensor above 100%RH and below 0%RH must be considered. As a consequence:
 118%RH corresponds to 0xFF which is the maximum RH digital output that can be sent out from the ASIC.
RH output can reach 118%RH and above this value, there will have a clamp of the RH output to this value.
 -6%RH corresponds to 0x00 which is the minimum RH digital output that can be sent out from the ASIC.
RH output can reach -6%RH and below this value, there will have a clamp of the RH output to this value.
 Relative Humidity conversion
With the relative humidity signal output SRH, the relative humidity is obtained by the following formula (result in
%RH), no matter which resolution is chosen:
RH

6
 125 
S _RH
2¹⁶
In the example given p.10, the transferred 16-bit relative humidity data is 0x7C80: 31872. The relative humidity
results to be 54.8%RH.
 Temperature conversion
The temperature T is calculated by inserting temperature signal output STemp into the following formula (result in
°C), no matter which resolution is chosen:
Temp

46.85
 175 .72

S_Temp
2¹⁶
SENSOR SOLUTIONS /// HPC202_5 HTU20D(F) Sensor Datasheet
9/2015
Page 16