L9680 datasheet(50/286 Pages) STMICROELECTRONICS

50 / 286 page

Start-up and power control

L9680

50/286

DS11615 Rev 7

6.10

VCOREMON external core voltage monitor

The device includes the possibility to monitor the external core voltage of MCU in case an

additional external regulator is used to provide the 1.2V rail. The internal power control state

machine will read the VCCSEL input pin and latch the resulting state upon the VCCBUCK

regulator enters in the VCC_ON state: if VCCSEL is lower than VTH1_L_VCCSEL the VCORE

monitor will be enabled, otherwise, if VCCSEL is higher than VTH1_H_VCCSEL, the VCORE

monitor will be disabled.

In summary:



VCCSEL < VTH1_L_VCCSEL (VCCSEL shorted to ground), to select VCC = 3.3 V and to

enable the VCORE monitor



VTH1_H_VCCSEL < VCCSEL < VTH2_L_VCCSEL (VCCSEL shorted to VCC), to select

VCC = 3.3 V and to disable the VCORE monitor.



VCCSEL > VTH2_H_VCCSEL (VCCSEL shorted to SYNCBOOST), to select VCC = 5 V

and to disable the VCORE monitor.

The VCORE monitor is enabled once the VCC regulator is in VCC_ON state, therefore the

external MCU core voltage regulator (1.2 V) must reach the regulation within 4ms after the

VCC regulator power-up.

Upon latching the VCCSEL state, the VCOREMON activation cannot be changed by the

user.

In case of VCCSEL open pin, an internal pull down current would force VCCSEL to ground

and then the VCORE monitor will be enabled function.

If the VCORE voltage is low and the VCCSEL pin is higher than VTH1_L_VCCSEL, after the

4ms delay from power-up, a latched VCOREMON fault will cause RESET to drive low, even

though VCCSEL pin is high enough to satisfy the disabling of VCOREMON function. This

occurs only once at power-up, and is then appropriately disabled. For this reason the

RESET is released 500 µs (namely the reset_hold_time) after the 4 ms delay from power-up

as showed in Figure 6.

L9680 датащи(PDF) 50 Page - STMicroelectronics