L9908 datasheet(56/152 Pages) STMICROELECTRONICS

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Figure 30. BT1 behavior timing diagram

Where:

1. BT1_DIS = ‘1’

BT1 is disabled and the direct connection from VPRE to CBS_n is opened, the current flow is prevented.

2. CBS_n – VPRE ≥ BT_lim1_ov_ltoh_th

BT1 is enabled and CBS_n voltage is lower than the overvoltage threshold. A direct connection from VPRE to

CBS_n is established and the current flow is controlled according to the current limiting feature:

–

As long as VPRE-CBS_n drop voltage is higher than the saturation mode threshold (~1.3 V) the current

sourced is almost constant and equal to BT_lim1_curr;

–

When the VPRE-CBS_n drop voltage falls below the saturation threshold the output stage enters the

linear operation and its behavior is assimilable to a resistance with value BT1_lim_res.

If the CBS_n voltage increases the BT1_lim_res increase until the BT_lim1_sat_drop is reached and the

sourced current falls to 0 mA.

3. CBS_n – VPRE ≥ BT_lim1_ov_htol_th

BT1 is enabled and CBS_n voltage is higher than the overvoltage threshold. An overvoltage is detected and

the connection from CBS_n to VPRE is opened to prevent the reverse current flow.

Table 53. Bootstrap limiter 1 electrical characteristics

Symbol

Parameter

Test condition

Min Typ Max Unit

Notes

BT_lim1_res

BT charge limiter1 limitation resistance

VPRE-CBS_n ≤ 1.3 V 90 120 150

Linear mode

[n = 1,2,3](1)

BT_lim1_curr

BT charge limiter1 limitation current

CBS_n = 0 V

118 160

Generator mode

[n = 1,2,3]

L9908

Functional description

DS13546 - Rev 5

page 56/152

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