EVB90615 Datasheet, PDF (10/30 Pages) Melexis Microelectronic Systems – Infra Red Thermometer

MLX90615
Infra Red Thermometer
Emissivity: Contains the value for object emissivity correction. The MLX90615 will compensate for the
emissivity of the object measured with respect to that value. The equation for that register is
ε Emissivity = dec2hex[round(16384 x )]
,where dec2hex[round(X)] represents decimal to hexadecimal conversion with round-off to nearest
value (not truncation). In this case the physical emissivity values are ε 0…1. For details about the emissivity
factor in IR measurements refer to the FAQ section of the current document.
Factory default is 4000h, which sets the thermometer to an emissivity of 1.0 (emissivity correction off).
8.3.4 RAM
RAM can be read through SMBus interface. Limited number of RAM registers, summarized below are of
interest to the customer.
RAM (16x16)
Name
Address Read access
Melexis reserved
0h
Yes
…
…
…
Melexis reserved
4h
Yes
Raw IR data
5h
Yes
TA
6h
Yes
TO
7h
Yes
Melexis reserved
8h
Yes
…
…
…
Melexis reserved
Fh
Yes
T_A is the MLX90615 package (ambient) temperature and T_O is the object temperature. The output scale is
0.02°K/LSB. To convert a read object temperature into degrees Celsius the equation is
To [°C] = RAM(7h)*0.02 – 273.15.
Raw IR data is in sign (1 bit, the MSB) and magnitude (15 bits) format.
8.4 SMBus compatible 2-wire protocol
The chip supports a 2 wires serial protocol, build with pins SDA and SCL.
• SCL – digital input, used as the clock for SMBus compatible communication. A low pulse on that pin
with duration t_REQ switches to the SMBus mode in case the PWM is selected in EEPROM. In case
PWM operation is desired, the SCL pin should be kept high. SMBus is the factory default (via
EEPROM settings).
• SDA/PWM – Digital input/ NMOS open drain output, used for both PWM and input/output for the
SMBus. (SMBus is factory default function).
8.4.1 Functional description
The SMBus interface is a 2-wire protocol, allowing communication between the Master Device (MD) and one
or more Slave Devices (SD). In the system only one master can be present at any given time [1]. The
MLX90615 can only be used as a slave device.
Generally, the MD initiates the start of data transfer by selecting a SD through the Slave Address (SA).
The MD has read access to the RAM and EEPROM and write access to 14 EEPROM cells (at addresses
0..Dh). If the access to the MLX90615 is a read operation, it will respond with 16 data bits and 8 bit PEC only
if its own slave address, programmed in the internal EEPROM, is equal to the SA, sent by the master. The
SA feature allows connecting up to 127 devices with 2 wires, unless the system has some of the specific
features described in paragraph 5.2 of reference [1]. In order to provide access to any device or to assign an
address to a SD before it is connected to the bus system, the communication must start with zero SA
followed by low RWB bit. When this command is sent from the MD, the MLX90615 will always respond and
will ignore the internal chip code information.
Note that EEPROM addresses 4h…Dh contain the factory calibration and should not be altered.
3901090615
Rev 001
Page 10 of 30
Data Sheet
28/Aug/2008