LT8610AB datasheet(24/28 Pages) AD

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LT8638S

Rev. 0

For more information www.analog.com

Temperature rise of the LT8638S is worst when operating

at high load, high VIN, and high switching frequency. If

the case temperature is too high for a given application,

then either VIN, switching frequency, or load current can

be decreased to reduce the temperature to an acceptable

level. Figure 8 shows examples of how case tempera-

ture rise can be managed by reducing VIN, switching fre-

quency, or load.

DEMO BOARD ON STILL AIR

L = XEL6060, XEL6030

VOUT = 3.3V

VIN = 12V, fSW = 400kHz, L = 2.2µH

VIN = 24V, fSW = 400kHz, L = 2.2µH

VIN = 12V, fSW = 2MHz, L = 0.47µH

VIN = 24V, fSW = 2MHz, L = 0.47µH

LOAD CURRENT (A)

100

110

120

130

Case Temperature Rise

8638S F08

Figure 8. Case Temperature Rise

The LT8638S’s internal power switches are capable of

safely delivering up to 12A of peak output current. However,

due to thermal limits, the package can only handle 12A

APPLICATIONS INFORMATION

loads for short periods of time. This time is determined by

how quickly the case temperature approaches the maxi-

mum junction rating. Figure 9 shows an example of how

case temperature rise changes with the duty cycle of a

1kHz pulsed 12A load.

DC2929A DEMO BOARD

VIN = 12V

VOUT = 3.3V

fSW = 2MHz

STANDBY LOAD = 0.25A

1kHz PULSED LOAD = 12A

DUTY CYCLE OF 12A LOAD

0.2

0.4

0.6

0.8

100

8638S G09

Figure 9. Case Temperature Rise vs 12A Pulsed Load

The LT8638S device’s top switch current limit decreases

with higher duty cycle operation for slope compensation.

This also limits the peak output current the LT8638S

can deliver for a given application. See curve in Typical

Performance Characteristics.

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