L9915 datasheet(5/21 Pages) STMICROELECTRONICS

5 / 21 page

DocID026400 Rev 1

5/21

L9915

Functional description

The device, supplied by the battery through B pin, remains in standby condition with low

current consumption until there is no activity on the pins L, C or PH. When the switch "Key"

is closed (i.e. VL>VLHTh) or the ECU communicates via C-Terminal protocol through C pin

(i.e. signal freq. on C pin between 100 Hz and 500 Hz) the device exits in standby condition

and goes in pre-excitation characterized by an activity on F pin with fixed frequency (fFSW)

and duty cycle (DFPreex). The device remains in pre-excitation until the alternator does not

run. When an activity is sensed on PH pin (i.e. VPH>VPHTh and fPH>fPHPrex) the device

starts to regulate; if the communication is present on C pin the regulator goes in external

regulation mode, otherwise it goes in internal regulation mode.

Another possibility for the device to start to regulate is the self start. In this way, although

there is no activity on pins L or C (for example due to connector open), if an activity is

sensed on PH pin (i.e. VPH>VPHTh and fPH>fPHPrex) the device goes in self start

characterized by an activity on F pin with fixed frequency (fFSW) and duty cycle (DFSS).

When the frequency on PH pin rises above fPSS the device starts to regulate with the

internal regulation mode.

The regulator stops to regulate when the frequency on PH pin falls below fPLPrex. If there is

activity on L or C pins the device stays in pre-excitation otherwise comes back in standby.

1.1

Application schematic

Figure 1. Application schematic

L9915 Datasheet(PDF) 5 Page - STMicroelectronics