ZSSC3122 Datasheet, PDF (19/64 Pages) List of Unclassifed Manufacturers – Low Voltage Capacitive Sensor Signal Conditioner

ZSSC3122 Datasheet
2.2.2 Temperature Measurement
The temperature signal comes from an internal PTAT (proportional to absolute temperature) circuit that is a meas-
ure of the die temperature. The PTAT (V_PTAT) voltage is used in the CDC to charge an internal capacitor (C_T),
while the bandgap voltage (V_BG) is used to charge the offset and the reference trimmable capacitors. The CDC
temperature output (Z_TEMP) is defined by equations (10) to (13):
Z _TEMP
=
2 ^RES
∗
(V_PTAT
/V_BG ) ∗ C_T
C_TREF
− C_TOFF
(10)
With
C_T = 1.44 ∗Temp _ Trim ∗1pF
(11)
With
C_TOFF = 1.44 ∗CDC _ Offset ∗1pF
(12)
And
C_TREF = 1.44 ∗ CDC _ Reference ∗ 1pF
(13)
Where
Symbol
Description
Z_TEMP
RES
Measured internal temperature
Programmable CDC resolution of 8, 10, 12, or 14 bits (bit setting in Table 5.4)
V_PTAT
V_BG
C_T
C_TOFF
C_TREF
Temp_Trim
Internal PTAT voltage
Internal bandgap voltage
Temperature measurement capacitor
Temperature CDC zero shift
Temperature reference capacitance
Temperature trim setting (bit setting in Table 5.4)
CDC_Offset
CDC offset trim setting (bit setting in Table 5.4)
CDC_Reference CDC reference setting (bit setting in Table 5.4)
Note: The factory settings for Temp_Trim, CDC_Offset, and CDC_Reference are optimized for the full
temperature range of -20°C to 125°C guaranteeing a minimum effective resolution of 13 bits when 14 bits of reso-
lution is selected. Unless a different temperature range is needed, it is strongly recommended that these settings
not be changed.
© 2016 Integrated Device Technology, Inc.
19
January 25, 2016