L9679P datasheet(49/272 Pages) STMICROELECTRONICS

49 / 272 page

DocID029275 Rev 1

49/272

L9679P

Start-up and power control

271

6.10

VSF regulator and control

The L9679P provides a low current linear regulator that can be used in the system design to

bias the external high side safing switch. The regulator output is 20 V nominal (configurable

to 25 V via SPI command). VSF is enabled if any of the ARMxINT signal is asserted, as

shown in Figure 24. The VSF regulator supply input is ERBOOST.

Figure 24. VSF control logic

VSF voltage can be monitored by the user through the internal ADC. Characteristics for this

function are shown in the electrical performance tables.

6.11

Oscillators

The device integrates two trimmed oscillators, both of them with spread spectrum capability

selectable via the CLK_CNF register.

The main oscillator runs at 16 MHz typ and is used to provide clock to the internal

synchronous logic. Moreover, this frequency is divided down by factor 8.5 to generate

clocks for the switching regulators (1.882 MHz typ).

The auxiliary oscillator runs at 7.5 MHz typ and is used to monitor the main oscillator. In

case the main oscillator frequency was lower the fOSC_LOW_TH threshold or higher than the

fOSC_HIGH_TH threshold, the condition is detected by the frequency monitor circuit and then

latched into the CLKFRERR flag in the FLTSR register and a POR is issued.

6.12

Reset control

The device provides reset logic to safely control system operation in the event of internal

ECU failures. Several internal reset signals are generated depending on the type of failure

detected. In Figure 25 the voltage monitoring diagram is shown.

L9679P 데이터시트(PDF) 49 Page - STMicroelectronics