STPMIC1 datasheet(43/140 Pages) STMICROELECTRONICS

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tSWINDB debounce timer is on SWIN detector output.

Note:

Regardless SWIN detector is enabled or not, PWR_SW is enabled only if VSWIN > VSWIN_Rise.

Soft-on/off – Switch implements soft-on, soft-off circuit. After the switch is enabled, switch starts operating in

“current limiting” mode, gradually increasing the output current limit until the switch is fully turned ON. This soft-on

phase has a duration defined by tSS_SWOUT.

The same mechanism is also applied during switch soft-off phase during turn-off to prevent quick unloading of

SWIN and excessive voltage overshoot.

Overcurrent limitation – Switch implements 2 levelsof overcurrent protection:

When load on the output exceeds overcurrent limit threshold ISWOUTOCP, switch starts limiting the output

voltage to decrease the output current. If the switch is in this condition for more than tOCPDBSW, switch is

automatically turned OFF, and SWOUT_OCP interrupt is generated.

In case output load exceeds ISWOUT_SH threshold, switch turns OFF immediately to prevent boost overload,

and SWOUT_SH interrupt is generated. Shortly after this action switch is re-enabled automatically with

standard soft-on current limiting procedure. In case overload condition is still present, switch continues the

operation in current limiting mode, and is finally switched OFF after tOCPDBSW. In case overload condition is

removed before tOCPDBSW switch continues its normal operation.

For a detailed behavior of the device on OCP event refer to Section 5.4.7 Overcurrent protection (OCP).

Output discharge – Switch implements a passive discharge circuit (by default disabled) that can be enabled by

setting SWOUT_PD bit in Table 48. BST_SW_CR register.

SWOUT pin is bidirectional but does not support reverse current protection:

•

Output: PWR_SW is turned ON (using SW_ON bit = ‘1’) only if SWIN voltage is higher than SWIN_Rise

threshold; else, PWR_SW keeps OFF. The SWIN rising and falling edge voltage (respectively VSWIN_Rise /

VSWIN_Fall thresholds) can be monitored by sending interrupt to host processor.

•

Input:

–

When PWR_SW is turned OFF (SW_ON bit = ‘0’), SWOUT pin monitors output voltage rising/falling by

sending interrupts to host processor. See VSWOUT_Rise / VSWOUT_Fall thresholds

–

When the STPMIC1 is in OFF (PWR_SW is implicitely turned OFF), SWOUT pin monitors a rising

voltage (SWOUT_Rise threshold) to generate power-up event. Refer to Section 5.4.2 Turn-ON

conditions.

•

PWR_SW has no reverse current protection voltage: SWIN should always be higher or equal to SWOUT

voltage to avoid reverse current flowing from SWOUT to SWIN

If PWR_SW switch is used to supply USB port from Boost converter (SWIN pin connected to BSTOUT

pin), then SWOUT_BOOST_OVP bit should be set in Table 70. NVM_LDOS_VOUT_SHR1 in order to

automatically turn OFF PWR_SW and clear SW_ON bit in case of boost OVP event occur. Reciprocally,

if PWR_SW is used as general-purpose power switch, SWOUT_BOOST_OVP bit should be clear in

Table 70. NVM_LDOS_VOUT_SHR1 in order to ignore boost OVP event. Reference to Section 5.4.8 BOOST

overvoltage protection.

Both of switches are controlled by VBUSOTG_ON / SWOUT_ON bit in Table 48. BST_SW_CR only. They

are always turned OFF when the STPMIC1 goes to POWER_ON (no NVM bit option to turn ON switches at

power-up) and are automatically turned OFF if the STPMIC1 POWER_DOWN.

Both of switches have a Pull_Down (PD) discharge resistor that is automatically enabled when switches are

turned OFF. PD discharge resistor can be disabled on PWR_USB_SW and PWR_SW by setting respectively

VBUSOTG_PD and SWOUT_PD bit in Table 48. BST_SW_CR register.

Both switches have overcurrent protection:

•

Safety features, see Section 5.4.7 Overcurrent protection (OCP).

•

An overcurrent detection can also be set as a turn-off condition – Section 5.4.7 Overcurrent protection

(OCP).

•

PWR_SW is selectable 500 mA/1000 mA power switch: overcurrent protection threshold is set by SW_OCP

bit in Table 48. BST_SW_CR.

PWR_USB_SW and PWR_SW switches (if SW_BOOST_OVP bit in Table 70. NVM_LDOS_VOUT_SHR1 is set)

are also disabled and their enable bits are cleared in case of boost OVP event.

STPMIC1

Boost converter and power switches

DS12792 - Rev 7

page 43/140

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