ADP1823ACPZ-R7 datasheet(24/32 Pages) AD

24 / 32 page

ADP1823

Rev. A | Page 24 of 32

The power dissipation heats the ADP1823. As the switching

frequency, the input voltage, and the MOSFET size increase, the

power dissipation on the ADP1823 increases. Care must be taken

not to exceed the maximum junction temperature. To calculate

the junction temperature from the ambient temperature and

power dissipation:

THERMAL CONSIDERATIONS

The current required to drive the external MOSFETs comprises

the vast majority of the power dissipation of the ADP1823. The

on-chip LDO regulates down to 5 V, and this 5 V supplies the

drivers. Because the full gate drive current passes through the

LDO and then is dissipated in the gate drive, effectively the full

gate charge comes from the input voltage and dissipated on the

ADP1823 is

(69)

)

(

(68)

The thermal resistance, θJA, of the package is typically 40°C/W

depending on board layout, and the maximum specified

junction temperature is 125°C, which means that at maximum

ambient of 85°C without airflow, the maximum dissipation

allowed is about 1 W.

where:

VIN is the voltage applied to IN.

fSW is the switching frequency.

Q numbers are the total gate charge specifications from the

selected MOSFET data sheets.

A thermal shutdown protection circuit on the ADP1823 shuts

off the LDO and the controllers if the die temperature exceeds

approximately 145°C, but this is a gross fault protection only

and should not be relied upon for system reliability.

ADP1823ACPZ-R7 数据表(PDF) 24 Page - Analog Devices