L9908 datasheet(54/152 Pages) STMICROELECTRONICS

54 / 152 page

Figure 29. VPRE operative ranges

5.11.4

Supply distribution stage

The supply distribution stage has the purpose to properly deliver the preregulated supply to LS and HS driver.

•

LS drivers are directly supplied by the VPRE voltage itself as it is referenced to GND and already

conditioned to fit the Ext. FET Vgs range for a correct driving. The supply distribution stage is then absent

for LS drivers.

•

HS drivers cannot use directly VPRE voltage as they need this voltage to be translated above VDH for a

correct Ext. FET driving. The supply distribution stage for each HS driver is then composed by the

cooperation of bootstrap circuits and a dedicated single Stage 2-Phases Dickson charge pump with

external capacitance.

Charge pump 2 (CP2) and bootstrap limiter 2 (BT2)

The purpose of CP2 is to guarantee a stable Vgs on HS FET during 100% (full-on) operations and to support the

bootstrap supply in “high” duty cycle PWM mode by recovering the static consumption of the three HS pre-drivers

in ON condition.

To carry out this function the CP2 structure generates a VDH+VPRE voltage onto the internal line VCP by means

of a current-limited single Stage 2-Phases Dickson charge pump with external capacitance (the tank capacitance

function of this stage is developed by the bootstrap capacitance itself).

When VDH < VDH_cp2_bst_mode_th the CP2 uses VPRE as input in both phases, resulting in an output voltage

equal to 2*VPRE.

Charge pump2 can be disabled by a dedicated SPI bit CP2_DIS within the register SAFETY_RELEVANT3 as

follows:

Table 50. Charge pump 2 enable bit

CP2_DIS

Description

Charge pump 2 enabled (Default)

Charge pump 2 disabled

Table 51. Charge pump 2 electrical characteristics

Symbol

Parameter

Test condition

Min Typ Max Unit

Notes

CP2_iout1

Total charge pump2 load

current

5.5 V ≤ VBP ≤ CP1_lin_mode_th

CFLY2 = 1 μF

SHS_n = VDH

INHn = 1

mA [n = 1,2,3]

L9908

Functional description

DS13546 - Rev 5

page 54/152

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