STWBC2-HP datasheet(45/96 Pages) STMICROELECTRONICS

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Figure 46. BB-DCDC block diagram overview

2.2.7.4

Charging step

The digital DC-DC controller uses a variable charging time to control the current in the coil:

•

The charge time is increased if the DC-DC does not reach the target regulation voltage during the discharge

phase. So, the next cycle furnishes more energy. The charge time increase is only applied if the coil current

does not reach the max. value.

•

The charge time is decreased if the target regulation voltage is overshot at the beginning of the discharge

phase. So, the next cycle furnishes less energy.

•

The charge time is also decreased if the output voltage is above the target at the end of the discharge step.

•

If the output voltage overshoots the target regulation voltage around the middle of the discharge phase, the

charge time is not modified.

2.2.7.5

Boost in QR mode

The drawing below shows a case of boost in QR mode where the control loop has converged. During the charge

phase, the output voltage drops because of the DC-DC load. During the discharge phase, the output voltage

passes above the target but not too early. So, the charge time is not changed. Furthermore, as the output voltage

is below the target at the end of discharge phase, a new charge cycle is engaged immediately.

Figure 47. QR mode converged loop operation

2.2.7.6

DCM case

The drawing below shows a DCM case where the output voltage is above the target at the end of the discharge

step. In this situation, the charge time is probably decreased because the output voltage overshoots the target too

early during the discharge step.

The charge time is also decreased because the output voltage stays above the target at the end of the discharge

phase. In addition, after the discharge step, the DC-DC controller waits for output voltage to be below the target to

start a new charge cycle. This is the way DCM and burst mode can operate.

STWBC2-HP

Digital AFE functions

DS13825 - Rev 1.0

page 45/96

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