L9963E datasheet(55/184 Pages) STMICROELECTRONICS

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For all regulators the slew rate at the power up can be evaluated considering corresponding current limitation

applied on capacitance connected to related pin. The equation below estimates the startup time considering a

20% tolerance on the external stabilization capacitance (refer to Table 73). The VREG regulator implements a soft

start strategy and its startup time is TVREG_SOFT_START.

TVCOMstart=VVCOM×CVCOM

IVCOM_curr_lim= 85−275 μs

TVTREFstart=VVTREF×CVTREF

IVTREF_curr_lim = 85−270 μs

TVANAstart=VVANA×CVANA

IVANA_curr_lim= 65−260 μs

(5)

Figure 18. Regular scheme

4.8.2

Bootstrap

In order to provide a supply higher than VBAT to the level shifters of the ADC, a Bootstrap solution has been

implemented. The Bootstrap is automatically enabled in NORMAL mode. The bootstrap works with an external

capacitance CCB.

Bootstrap works in 2 phases:

•

during phase 1 capacitance CCB is charged between 0 V and VREG for a time long TRELOAD_PHASE.

•

during phase 2 the same capacitance is bootstrapped, connecting its negative terminal to VBAT. This phase

longs TBOOT_PHASE.

A VREG OV condition turns off bootstrap circuit.

L9963E

Device regulators

DS13636 - Rev 12

page 55/184

L9963E Arkusz danych(PDF) 55 Page - STMicroelectronics