User Manual

Application Note
SMBus communication with MLX90614
390119061402 Page 25 of 32 Jan-2008
Rev 004
7 Sleep Mode
MLX90614 can enter Sleep Mode via command “Enter SLEEP mode” sent via the SMBus
interface. This mode is not available for the 5V supply version. To limit the current consumption
to 2.5uA (typ), the SCL pin should be kept low during sleep (Fig.9). MLX90614 goes back into
power-up default mode (via POR reset) by setting SCL pin high and then PWM/SDA pin low for
at least t
DDq
=14ms (Fig.10).
Fig.9 Fig.10
After the module is awakened and before reading the temperature, an additional delay is
required or the first measurements will not be correct. This additional delay depends on the FIR
filter.
(After wake-up the digital part of the MLX90614 is restarted, IIR =100% for the first temperature
calculation flow from the module, see Fig.11. After this first temperature calculation flow from the
module, IIR restores its value to the value before the module was put in sleep mode).
See AppNote ”Understanding MLX90614 on-chip digital signal filters” on
http://www.melexis.com/Asset.aspx?nID=5272 to understand how to calculate this delay time.
Initialization
T
A
Offset meas
OS
Ta
= meas(N
Tos
)
filtering
T
OS
= IIR(L
Tos
,OS
Ta
)
T
A
meas
T
DATA
= meas(N
Ta
)
Offset comp
T
DATAcomp
= T
DATA
-T
OS
filtering
T
D
= IIR(L
Ta
,T
DATAcomp
)
T
A
calculation
T
A
IR Offset meas
OS
IR
= meas(N
IRos
)
filtering
IR
OS
= IIR(L
IRos
,OS
IR
)
IR1 meas
IR1
D
= meas(N
IR
)
Offset comp
IR1
Dcomp
= IR1
D
- IR
OS
filtering
IR1
D
= IIR(L
IR
,IR1
Dg
)
T
OBJ1
calculation
Gain drift
IR
Gm
= meas(N
IRg
)
Offset comp
IR
Gcomp
= IR
Gm
- IR
OS
filtering
IR
G
= IIR(L
G
,IR
Gcomp
)
K
G
calculation
IR offset
Gain comp
IR1
Dg
= IR1
Dcomp
*K
G
IR2 meas
IR2
D
= meas(N
IR
)
Offset comp
IR2
Dcomp
= IR2
D
- IR
OS
filtering
IR2
D
= IIR(L
IR
,IR2
Dg
)
T
OBJ2
calculation
Gain comp
IR2
Dg
= IR2
Dcomp
*K
G
T
OBJ1
T
OBJ2
PWM calculation
Load PWM registers
1
1
2
3
2
3
Fig.11