MLX90615

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MLX90615Infra Red Thermometer8.5.2 Request conditiont REQSCLFigure 13: Request (switch to SMBus) conditionIf PWM is enabled, the MLX90615’s SMBus Request condition is needed to disable PWM and reconfigureSDA/PWM pin before starting SMBus communication. Once disabled, PWM can only be enabled byswitching the supply Off-On. The MLX90615’s SMBus request condition requires forcing the SCL pin LOW fora period longer than the request time (t REQ ). The SDA/PWM line value is ignored in this case.8.5.3 PWM is disabledSMBus RequestIf PWM is disabled by means of EEPROM the SDA/PWM pin is directly used for the SMBus communicationafter POR.3901090615 Page 16 of 30 Data SheetRev 00128/Aug/2008
MLX90615Infra Red Thermometer8.6 PWMThe MLX90615 can be read via PWM or SMBus compatible interface. Selection of PWM output is done inEEPROM configuration (factory default is SMBus). Object or ambient temperature can be read through PWM.The PWM period is derived from the on-chip oscillator and is programmable in a low or high frequency.Config Register[2:0] PWM data PWM frequency000 To High010 To Low100 Ta High110 Ta Lowxx1SMBus, PWM disabledTemperature ranges for the PWM output are written in EEPROM 0x0, 0x1 – PWM Tmin and PWM Trange(Tmax-Tmin), scale is 0.02°K/LSB. Note that in SMBus mode the EEPROM 0x0 is used for Slave addressSA.8.6.1 PWM formatFigure 14: PWM formatThe temperature reading can be calculated from the signal timing as:⎡2t⎤Tout = 2⎢* Trange + Tmin⎣ T ⎥,⎦where Tmin and Trange are the corresponding rescale coefficients in EEPROM for the selected temperatureoutput and T is the PWM period. Tout is To or Ta according to bit Config Register, 2.The different time intervals t 1 , t 2 and t 3 have the following functions:t 1 : Start buffer. During this time the signal is always high. t 1 = 0.125*T (T is the PWM period, refer to fig. 14).t 2 : Valid Data Output Band, 0 to 1/2T. PWM output data resolution is 10 bit.t 3 : Low time. The maximum duty cycle is limited to t 1 + t 2 = 0.625 This means that the PWM line will never gostatic, allowing detection of fault on the line (disconnected device, short on the line).Example:T o => Config Reg,2 = 0To min = 0°C => PWM T min [EEPROM] = 50 * (to min + 273.15) = 355BhTo max = To min + T range = +50°C => PWM T range [EEPROM] = 50 * (to range) = 09C3hCaptured PWM high duration is 0.495*T => t 2=(0.495 – 0.125)*T=0.370*T =>measured object temperature = 2X0.370* (50°C -0°C)+0°C = +37.0°C.3901090615 Page 17 of 30 Data SheetRev 00128/Aug/2008
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MLX90615

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