AN2808 datasheet(29/40 Pages) STMICROELECTRONICS

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AN2808

PM6670S evaluation tests

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10.10.2

Switching frequency vs output current

The switching frequency can decrease to very low values in pulse-skip mode, whereas in

non-audible pulse-skip there is a lower limit (about 33 kHz). With increasing loads, however,

the switching frequency increases slightly as a consequence of conduction and switching

losses.

Figure 35.

fsw vs iload, Vin = 12 V voltage, DDR2(c)

10.11

Thermal behavior

The IC’s internal maximum and average temperature can be monitored by an IR camera.

For the following measures the test setup is:

●

VIN =12 V

●

FSW = 360 kHz

●

Pulse skip mode

●

IVDDQ = 8 A

●

VTT rail powered by VDDQ

●

TAMB = 26° C

When the VTT current is increased, the IC temperature changes as shown in the following

charts.

Forced PWM (blue), no-audible pulse-skip (purple) and pulse-skip (yellow). Switching frequency vs output

current, VDDQ = 1.8 V, no load.

100

150

200

250

300

350

400

450

500

0.001

0.01

0.1

Output current (A)

AM00660v1

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