L9680 datasheet(46/286 Pages) STMICROELECTRONICS

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Start-up and power control

L9680

46/286

DS11615 Rev 7

Figure 20. ER switch state diagram

6.7

SYNCBOOST boost regulator

The SYNCBOOST boost regulator also operates at 1.882 MHz allowing the user to select

smaller less expensive external components. The regulator provides a 12 V/14.75 V

nominal for the sync pulse feature used in PSI-5 bussed satellite sensor configuration. The

regulator also provides the power for the SATBUCK regulator.

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

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

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

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

IOC_SYNCBST value to the maximum one with 16 steps and within 1024 µs. The soft start is

restarted every time the regulator is enabled, namely there is a transition from the

SYNCBOOST_OFF state to the SYNCBOOST_ON state.

In normal operation, the SYNCBOOST regulator operates directly from battery providing a

voltage level to operate the sync pulse driver circuit. Should the input voltage be greater

than regulation point, the output voltage will track the input voltage less any drops in the

external components.

The boost regulator is enabled automatically by the power control state machine, but can be

disabled on purpose via SPI command through the SYS_CTL(SYNCBST_EN) bit. The

regulation point is fixed at a nominal 12 V at startup. User may increase the output

regulation voltage to 14.75 V nominal by setting the SATV bit via a dedicated SPI command,

should an extended voltage range be needed.

Boost converter diagnostics include over voltage and under voltage, reported by the

S_BST_NOK bit in the POWER_STATE register, and the circuit is fully protected against

shorts. The integrated FET featuring the boost switch is protected against short to battery by

means of a thermal shutdown circuit. When thermal fault is detected the FET is switched off

and latched in this state until the related fault flag ERBST_OT in the FLTSR register is read.

ER Switch

ER_switch_ON

POR

ER_switch_OFF_OT

T1 Timeout

ER_switch_STBY

Start T1 1 ms

ER_SWITCH_TSD = 0

(ER_SWITCH_TSD = 1

AND

“deployment not in progress”)

(ER_SWITCH_TSD = 1

AND

“deployment not in

progress”)

ER_SWITCH_TSD = 1

“Deployment in progress”

ER_SW_OV = 1 when VIN - VER > Ver_sw_ov_th

ER_SW_OV = 0

AND

Passive_mode = 1

ER_SW_OV = 1

Passive_mode = 0

ER_switch_OFF

GAPGPS02265

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