Rainbow Electronics MAX14821 - Manual (Page 18)

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MAX14821
IO-Link Device Transceiver
Thermal Protection and Considerations
The internal LDOs and drivers can generate more power
than the package for the device can safely dissipate.
Ensure that the driver LDO loading is less than the pack-
age can dissipate. Total power dissipation for the device
is calculated using the following equation:
P
TOTAL
= P
C/Q
+ P
DO
+ P
5
+ P
LDO33
+ P
Q
+
P
CLCQ
+ P
CLDI
where P
C/Q
is the power generated in the C/Q driver,
P
DO
is the power dissipated by the DO driver, P
5
and
P
LDO33
are the power generated by the LDOs, P
Q
is the
quiescent power generated by the device, and P
CLCQ
and P
CLDI
are the power generated in the C/Q and DI
current sinks.
Ensure that the total power dissipation is less than the
limits listed in the
Absolute Maximum Ratings section.
Use the following to calculate the power dissipation (in
mW) due to the C/Q driver:
P
C/Q
= [I
C/Q
(max)] Ч [0.5 + 7 Ч I
C/Q
(max)]
Calculate the internal power dissipation of the DO driver
using the following equation:
P
DO
= [I
DO
(max)] Ч [0.5 + 7 Ч I
DO
(max)]
Calculate the power dissipation in the 5V LDO, V5, using
the following equation:
P
5
= (V
LDOIN
- V
5
) × I
5
where I
5
includes the I
LDO33
current sourced from
LDO33.
Calculate the power dissipated in the 3.3V LDO, LDO33,
using the following equation:
P
LDO33
= 1.7V × I
LDO33
Calculate the quiescent power dissipation in the device
using the following equation:
P
Q
= 5mA × V
CC
(max)
If the current sinks are enabled, calculate their associ-
ated power dissipation as:
P
CLCQ
= 7mA × V
C/Q
(max)
P
CLDI
= 7mA × V
DI
(max)
Overtemperature Warning
Bits in the Status and Mode registers are set when the
temperature of the device exceeds +115NC (typ). The
OTempInt bit in the Status register is set and IRQ asserts
when the OTemp bit in the Mode register is set. Read the
Status register to clear the OTempInt bit and IRQ.
The OTemp bit is cleared when the die temperature falls
to +95NC.
The device continues to operate normally unless the
die temperature reaches the +150NC thermal shutdown
threshold, when the device enters thermal shutdown.
Thermal Shutdown
All regulators and the C/Q and DO output drivers are
automatically switched off when the internal die tempera-
ture exceeds the +150NC (typ) thermal shutdown thresh-
old. SPI communication is not available during a thermal
shutdown event.
Regulators are automatically switched on when the inter-
nal die temperature falls below the thermal shutdown
threshold plus hysteresis. The internal registers return to
their default state when the V
5
regulator is switched on.