SSL4120 datasheet(14/48 Pages) NXP

14 / 48 page

SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

14 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

Figure 6 shows the operation of the restart timer. Normally Cprot is discharged to 0 V.

When a restart is requested, Cprot is quickly charged to the upper switching level

Vu(RCPROT). Then the RCPROT pin becomes high ohmic and Cprot discharges through

Rprot. The restart time has elapsed when VRCPROT reaches the lower switching level

Vl(RCPROT) = 0.5 V. The IC restarts and Cprot is discharged.

7.5.3 Fast shut-down reset (SNSMAINS pin)

The latched Protection shut-down state is reset when VSUPIC and VSUPHV drop below their

respective reset levels, Vrst(SUPIC) and Vrst(SUPHV). Typically, the PFC boost capacitor

Cboost, must discharge before VSUPIC and VSUPHV drop below their reset levels.

Discharging Cboost can take a long time.

Fast shut-down reset causes a faster reset. When the mains supply is interrupted, the

voltage on the SNSMAINS pin falls. When VSNSMAINS falls below Vrst(SNSMAINS) and then

increases again by a hysteresis value, the IC leaves the Protection shut-down state. The

boost capacitor Cboost does not require discharging to trigger a new start-up.

The Protection shutdown state is also exited by pulling down the enable input (the

SSHBC/EN pin).

7.5.4 Output overvoltage protection (SNSOUT pin)

The SSL4120 outputs are provided with overvoltage protection (OVP output; see

Section 7.9). The output voltage is measured using the resonant transformer auxiliary

winding. The voltage is sensed on the SNSOUT pin using an external rectifier and

resistive divider. An overvoltage is detected when the SNSOUT voltage exceeds

Vovp(SNSOUT). When an overvoltage is detected, the SSL4120 enters the Protection

shut-down state.

Additional external protection circuits, such as an external OTP circuit, can be connected

to this pin. Connect them to the SNSOUT pin using a diode to ensure that an error

condition triggers an OVP event.

Fig 6.

Operation of the restart timer

passed

yes

Vu(RCPROT)

Vl(RCPROT)

Restart request

014aaa854

VRCPROT

Restart time

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