PSoC
®
Thermal Management Expansion Board Kit Guide, Doc. No. 001-89649 Rev. **
19
3.4 Diode Analog Temperature Sensors
The CY8CKIT-036 EBK has two transistors connected in the diode configuration that can be used for temperature
measurement. This section briefly describes the principle behind diode temperature measurement.
The following equation gives the current
, through a forward-biased diode:
Equation 1
Where:
is the diode-forward voltage drop
is the reverse saturation current
is a constant (called ideality factor) that has a value between 1 and 2, depending on the material and the physical
structure of the diode
is the thermal voltage given by the equation:
Equation 2
Where:
is th
e Boltzmann’s constant
is the absolute temperature in Kelvin
is the magnitude of electronic charge
By passing two currents I1 and I2 and measuring the respective voltages V1 and V2, the temperature can be calculated
using the following equation:
Equation 3
For details on interfacing with a diode temperature sensor using various PSoC devices, read the following application notes:
AN78920
– PSoC 1 – Temperature Measurement Using a Diode
AN60590
– PSoC 3, PSoC 4 and PSoC 5LP – Temperature Measurement with a Diode
The code examples in the application note use an external calibration resistor for measuring the current ratio accurately.
The calibration resistor is not part of CY8CKIT-036 and needs to be connected externally on the PSoC DVK used. Refer to
the respective PSoC application notes for the value of the calibration resistor and for connection details.
3.5 One-Wire Temperature Sensor
The CY8CKIT-036 EBK has an onboard Maxim DS18S20 one-wire, high-precision digital temperature sensor. The one-wire
interface is a bidirectional, half-duplex, serial signaling protocol designed by Dallas Semiconductor. This compact
communication interface for ICs does not require high-speed communication. It uses a single wire for reading and writing,
and has no clock signal. One-wire devices have the ability to operate in parasitic mode, in which the connected devices can
draw power from the one-wire bus itself. A one-wire interface is relatively slow, with a typical data rate of 16 kbps. It is
perfect for slow sensors, such as thermometers, that do not need to be polled frequently.
For using PSoC 1 to interface with a one-wire temperature sensor, refer to the application note:
AN2163
– Interfacing to
One-Wire/Two-Wire Digital Temperature Sensors Using PSoC 1
. Currently, there is no support for one-wire temperature
sensors in the PSoC Creator IDE for PSoC 3, PSoC 4, or PSoC 5LP devices. Contact Cypress Technical Support if you
need one-wire temperature sensor support for these PSoC devices.
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