L9788 datasheet(68/264 Pages) STMICROELECTRONICS

68 / 264 page

Multi-voltage regulator supplies

L9788

68/264

DS12308 Rev 4

Figure 26. Boost threshold comparator's schematic

6.2

Pre-buck regulator with internal MOS

Vpre features:



6 V regulated output voltage (VPRE);



1.6 A maximum output current;



PWM block (ramp generator, comparator and main latch) with one fixed PWM

frequency (Fsw_vpre);



Internal error amplifier;



Internal Power FET including Bootstrap;



dV/dt Control on gate drivers to fulfill EMC requirements;



Maximum Duty cycle 100%, to allow to charge Bootstrap capacitor;



Protection by over temperature;



Soft Start.

The Vpre regulator is a buck regulator which supplies Pre-boost driver/VDD5/Vtrack1.2.3.

When the OV of VB_IN is detected, the Vpre(Buck) will be switched off. This function is

selectable by a dedicated MSC bit (VB_IN_OV_RST_EN in CONFIG_REG12). A bit is also

available (BUCK_SLOW_SR in CONFIG_REG 21) in order to select slew rate for output

voltage; the default value corresponds to fast slew rate, slow slew rate helps to improve

emission performance

The Vpre regulator includes a soft start. Range of dV/dt at VPRE is specified in electrical

parameters.

Pulse skipping mode: the Vpre regulator can go to pulse skipping mode when the load is too

low to avoid that output voltage (VPRE) rises too much. The principle of the pulse skipping

mode is to skip some pulses during the switching phase, when the loop can't keep itself the

output voltage regulated with a very low load because it is limited by the minimum duty

cycle.

VB_IN_OV fault can trigger the turn OFF of Buck regulator, as specified into reset matrix.

This effect can be masked with bit VB_IN_OV_RST_EN in CONFIG_REG 12.

VBAT_sense

Vbg

Vcomp_th1

Vbg

Vcomp_th2

Vbg

Vcomp_th3

Vbg

Vcomp_th4

GADG2911161610PS

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