L99LD02 datasheet(14/66 Pages) STMICROELECTRONICS

14 / 66 page

Boost controller

L99LD02

14/66

DS12448 Rev 3

The voltage range and the granularity are defined to give flexibility because of internal

output divider: the control loop regulates the output voltage on BST_OUT pin looking to the

internal feedback voltage.

Device output voltage is configurable via SPI (see CR#2 Bit[11:5], BST_OUT in Table 23:

CR#2: Control Register 2) or through dedicated OTPs (for stand-alone configuration).

3.4

Overvoltage protection

The peak current mode requires a minimum on-time, because of the noise generated right

after the turn-on of the switching MOSFET. At light load (very low output current), this

minimum on-time, in combination with the selected switching frequency is no longer able to

regulate the output voltage to the requested voltage. The device enters in overvoltage

protection (OVP), in order to prevent an excessive rise of the boost output voltage above the

target voltage.

This mode is activated when the voltage on BST_OUT pin is higher than the selected of a

specified threshold value (VBST_OUT_OV_ON).

The switching activity is resumed as soon as the voltage on BST_OUT pin decreases to the

selected one. In case of BST_OUT voltage increases above VBST_OUT_OV_ON, an

output digital flag, called BST_OVP, is set. As soon as the output voltage decreases down to

programmed target value (BST_OUT [xxxxxx]), the bit is reset after tBST_OVP_RST delay time

(10ms typical). This delay time is implemented in order to eliminate the diagnostic ambiguity

(toggling of the OVP flag) during permanent no load or light load operation.

BST_OVP bit is not set in case of boost disabled.

3.5

Output failure protection

The L99LD02 is protected in case of boost controller output voltage pin failure. More in

detail, a specific bit, called BST_OUT_FAIL (see SR#1 Bit[6], BST_OUT_FAIL in Table 26:

SR#1: Status Register 1), is set in case of output voltage pin (BST_OUT) pin is left floating

or shorted to ground.

This bit is set:



If device is OFF, boost controllers do not start;



If device is ON in



single/dual phase configuration, boost controllers are immediately switched OFF;



If device is ON in three/four phases configuration and it is in Active mode: both

Master/Salve devices are switched off when the failure is recognized on Master side;

only Slave device is switched off when the failure is recognized on Slave side while the

Master is managed by the microcontroller;



If device is ON in three/four phases configuration and it is in Limp Home: both

Master/Salve devices are switched off when the failure is recognized on Master side;

only Slave device is switched off when the failure is recognized on Slave side, while the

Master is forced to work at minimum duty cycle.

The reset of BST_OUT failure bit is demanded to the microcontroller (in Active mode) or to

an auto-restart function (in Limp Home) that cyclically clears this bit with a period equal to

tAUTORESTART.

This bit is not set if BST_DIS bit is set.

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