L99LD02 datasheet(12/66 Pages) STMICROELECTRONICS

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Supply concept

L99LD02

12/66

DS12448 Rev 3

Supply concept

The L99LD02 supply range is from 3V up to 28V, which guarantees compatibility with 12V

systems. The device is normally supplied from VS pin; when battery level is not enough to

guarantee well driven external MOSFETs, the device supply is switched to BST_OUT pin.

The device supply is from:



VS, in the range of Vs_sw up to Vsmax;



BST_OUT when Vs < Vs_sw and Bst_out > Bst_Out_min (15V typical).

Vs_sw is determined from minimum gate driver voltage (7V typical) and voltage drop

between Vs and gate driver output. Vsmax is 40V to be compatible with 12V system load

dump.

This supply concept guarantees boost functionality during cranking, according to ISO16750-

2 and LV124. The L99LD02 output voltage regulation in cranking is ensured according to

the following formula:

Bst_Out = Vin * ƞ * 1 / (Toff_min * Fsw)

where Vin is the minimum boost input voltage during cold cranking condition (3.2V), ƞ is

L99LD02 typical efficiency, Toff_min is the minimum off time value specified for the full spec

range, Fsw is the operative switching frequency of the device.

In cold cranking, boost operation and protection functions are kept. The output power is

limited only by adjusted input current limit and converter Toff_min, whilst, full functionality -

without any limitation - is ensured from VS ≥ Vs_min (minimum operating supply voltage,

5.5V typical).

VS under-voltage shutdown function is implemented to avoid an operation of the external

mosfet of the boost controller in linear mode, due to a too low gate driver supply. In case the

VS falls below VS under-voltage threshold (Vs_uv), while device is not supplied from

BST_OUT (BST_OUT < BST_OUT_MIN), the device disables the boost operation. Configu-

ration, operating mode and diagnostic data are kept down to POR.

L99LD02 датащи(PDF) 12 Page - STMicroelectronics