L9679P datasheet(38/272 Pages) STMICROELECTRONICS

38 / 272 page

Start-up and power control

L9679P

38/272

DocID029275 Rev 1

Figure 10. IC operating state diagram

6.3

ERBOOST switching regulator

The L9679P IC uses an advanced energy reserve switching regulator operating at

1.882MHz nominal. The higher switching frequency enables the user to select smaller less

expensive inductors and moves the operating frequency to permit easier compliance with

system emissions.

The ERBoost switching regulator uses a classical peak current mode control loop to

properly regulate the output voltage and includes an over-voltage protection that

immediately switch off the PowerMOS to protect the device. The regulator includes also a

soft start circuit which apply a ramp on the over current threshold from the 40% of

IOC_ERBST value to the maximum one with 16 steps and within TSOFTST_OC_ERCBST. The

soft start is restarted every time the regulator has a transition from the ER_BST_OFF to the

ER_BST_ON state.

The energy reserve boost regulator charges the external system tank capacitor through an

integrated fixed current source significantly reducing in-rush currents typical of large energy

reserve capacitors. The boost circuit provides energy for the reserve capacitor with

assumed run time load of less than 20 mA and to the VSF regulator. Once system shutdown

is initiated or a loss of battery condition is diagnosed, the boost regulator is by default

disabled so that system power can be taken from the energy reserve capacitor.

Alternatively, the ER Boost could be kept on even during the ER State by setting the

SYS_CFG(KEEP_ER_BOOST_ON) bit.

The energy reserve boost regulator defaults to 23 V at power-on and can be set to 33 V

nominal by the user through an SPI command. The boost converter can also be disabled by

the user through an SPI command. Enabling, disabling and setting the boost output voltage

L9679P Datasheet(PDF) 38 Page - STMicroelectronics