ft≈ 12π nVin

nVout+VinRsenseSecGTV

Rsense 1FckVCSFSR 1TsampPIDCC_Igain

(16)

The gain can be set as:

PIDCC_Igain=ft2πRsenseFckVCSFSRTsamp

RsenseSecGTV nVoutVin+1n

(17)

It is advisable to keep the cutoff frequency at least below 1/5 of the loop sampling frequency, i.e. below 8 kHz. If

no need for fast transient response is required, a lower bandwidth helps in limiting the control noise.

8.6.5

Cable drop compensation

The cable drop compensation allows to increase the output voltage of the converter proportionally to the current

sensed through the CSP/CSM pins.

The cable drop compensation is disabled when the output voltage set by the USB-PD port is above a

programmable threshold.

The cable resistance to be compensated can be programmed in the configuration parameters.

8.7

Fault management

The IC includes many protections to avoid damage to the converter or to the load in abnormal or failure

conditions.

8.7.1

Fault modes

The faults can be either managed as auto-restart, latched, or conditioned restart.The behavior of each fault is

described in Fault summary.

8.7.1.1

Auto-restart mode

In auto-restart mode, once the protection is tripped, the switching activity is stopped, and the condition is

maintained until VPVCC goes below the V PVCCOff restart voltage and then rises again to V PVCCOn for six times.

Ultimately, this results in a low frequency intermittent operation (Hiccup-mode operation).

8.7.1.2

Latched mode

In latched mode the protection is maintained until the input main is removed. During this time the HV generator

is activated periodically to cycle the supply voltage between V PVCCOn and V PVCCOff. The condition is indefinitely

maintained until the AC mains is removed triggering a brown-out or an X-Cap discharge fault which clears all fault

conditions.

8.7.1.3

Conditioned restart mode

Faults like the overtemperature or the brown-out, require the fault condition to disappear before the system can

restart. When the fault condition is no longer present the system restarts after VPVCC goes below V PVCCOff restart

voltage and then rises again to V PVCCOn.

8.7.2

Soft-start timeout

As a protection from secondary side failures, the IC stops switching if no signal is received from the secondary

side before the SS pin voltage reaches VSSEND.

This fault is managed as auto-restart.

8.7.3

Soft-start overvoltage protection

The primary side IC includes a detection circuit to avoid generating overvoltage on the output when the secondary

side is not active. The OV function operates only during primary side soft-start: as the secondary side takes

control, the protection is managed by the secondary side.

The overvoltage function of the ST-ONEMP device monitors the voltage on the OVP pin during HS MOSFET's

on-time, when the voltage generated by the auxiliary winding tracks converter's output voltage.

ST-ONEMP

Fault management

DS13989 - Rev 2

page 23/39