L9908 datasheet(55/153 Pages) STMICROELECTRONICS

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Figure 29. VPRE operative ranges

5.11.4

Supply distribution stage

The supply distribution stage has the purpose to properly deliver the pre-regulated 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. 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. 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 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 will use 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

Gate driver supply

DS13546 - Rev 3

page 55/153

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