Nexperia

NEX8080 series

Wide Vcc range multi-mode flyback controller

9.3.2. Brown-in/brown-out

In addition to the detection of VCC voltage, the input line voltage is also checked before the soft start is initiated. When the

primary MOS is turned on, the induced auxiliary winding voltage is negative, generating a current flowing out from the ZCD

pin. See Fig. 14 for reference.

NAUX

RZT

RZB

ZCD

Vth

Iline

aaa-040376

Fig. 14. Resistor divider at ZCD

Since the ZCD voltage is clamped at ~0 V by an internal circuit, this current is proportional to input voltage and can be

calculated as shown in Equation 1:

(1)

where NPRI and NAUX are the number of turns of primary winding and auxiliary winding respectively, and

RZT is the top side resistor of the divider from auxiliary winding to ZCD pin.

Each time VCC is higher than VCC_ON, the NEX8080x will send out several narrow pulses to turn on the primary MOS, and

then detect Iline. If Iline>IBNI (brown-in threshold current), the NEX8080x will initiate soft start process. Otherwise it will restart.

During the normal working period, Iline is always checked when the primary MOS is turned on. If Iline drops below IBNO

(brown-out threshold current) for a continuous period larger than tD_BNO (~50 ms), NEX8080x will restart. The timing

sequence of brown-out is shown in Fig. 15.

VCC_ON

VCC_OFF

VCC

Brown-out

timer

Time out

TD BNO

Brown-out

VBULK

VBNI

VBNO

aaa-040377

Resumed

Fig. 15. Timing sequence of brown-out

NEX8080_series

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Nexperia B.V. 2024. All rights reserved

Product data sheet

Rev. 1 — 30 September 2024

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