NCP5331 datasheet(22/38 Pages) ONSEMI

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NCP5331

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Power Dissipation

NCP5331 power dissipation may be approximated by the

following equation:

Ploss + FSW ·(VCCH ·QTHighFETs

) VCCLx ·QTLowFETs) ) PQuiescent

where:

PQuiescent + VCCL ·ICCL ) 2· VCCLx ·ICCLx

) (VCCH ) Vin)·ICCH

FSW is the switching frequency

VCCL is 12 V

VCCLx is the low-side gate drive voltage and may be varied

between 5.0 and 12 V

VCCH is the high-side gate drive voltage and is between 4.5

and 7.0 V

Vin is the input voltage to the converter and is either 5.0 or

12 V

ICCL, ICCLx, ICCH are typical device quiescent currents and

can be found under the General Electrical Specifications.

QTHighFETs is the sum of the High-Side MOSFets total gate

charge

QTLowFETs is the sum of the Low-Side MOSFets total gate

charge

Figure 29 shows device temperature rise versus switching

frequency at various gate drive voltage combinations using

ON Semiconductor’s NTD60N03 (Qt = 31nC at 5.0 V) as

the high-side MOSFet and NTD80N02 (Qt = 39nC at 7.0 V)

as the low-side MOSFet. Using other MOSFets will of

course result in different losses, but the general conclusion

will be the same.

If trying to drive 2 lower MOSFets at frequencies higher

than 200 KHz, it may be necessary to reduce the low-side

gate drive voltage.

Figure 29. Calculated NCP5331 temperature rise (LQFP-32 package)

versus frequency at various typical gate drive voltage combinations

with typical ON Semiconductor MOSFets.

100

150

200

250

300

350

FREQUENCY (kHz)

VCCH = 4.5 V;

VCCLx = 12 V;

1 Low-Side FETS

VCCH = 4.5 V;

VCCLx = 12 V;

2 Low-Side FETS

VCCH = 7.0 V;

VCCLx = 12 V;

2 Low-Side FETS

VCCH 4.5 V;

VCCLx = 12 V;

2 Low-Side FETS

VCCH = 7.0 V;

VCCLx = 12 V;

1 Low-Side FETS

VCCH = 7.0 V;

VCCLx = 12 V;

2 Low-Side FETS

NCP5331 Datasheet(PDF) 22 Page - ON Semiconductor

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