MAX14821 datasheet(18/29 Pages) MAXIM

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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:

PTOTAL = PC/Q + PDO + P5 + PLDO33 + PQ +

PCLCQ + PCLDI

where PC/Q is the power generated in the C/Q driver,

PDO is the power dissipated by the DO driver, P5 and

PLDO33 are the power generated by the LDOs, PQ is the

quiescent power generated by the device, and PCLCQ

and PCLDI 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:

PC/Q = [IC/Q(max)] × [0.5 + 7 × IC/Q(max)]

Calculate the internal power dissipation of the DO driver

using the following equation:

PDO = [IDO(max)] × [0.5 + 7 × IDO(max)]

Calculate the power dissipation in the 5V LDO, V5, using

the following equation:

P5 = (VLDOIN - V5) × I5

where I5 includes the ILDO33 current sourced from

LDO33.

Calculate the power dissipated in the 3.3V LDO, LDO33,

using the following equation:

PLDO33 = 1.7V × ILDO33

Calculate the quiescent power dissipation in the device

using the following equation:

PQ = 5mA × VCC(max)

If the current sinks are enabled, calculate their associ-

ated power dissipation as:

PCLCQ = 7mA × VC/Q(max)

PCLDI = 7mA × VDI(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

When the die temperature rises above the +150°C (typ)

thermal shutdown threshold, the C/Q and DO drivers and

the C/Q and DI current loads are automatically turned off.

The internal 3.3V and 5V LDOs remain on during thermal

shutdown, if enabled. If the internal or external V5 supply

remains on during thermal shutdown (which is always

true in case of the internal V5 regulator), the register con-

tents are maintained and SPI communication is available.

When the die temperature falls below the thermal shut-

down threshold plus hysteresis, the C/Q and DO drivers

and C/Q and DI current sinks turn on automatically.

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