Rev. F 05/18

7

LinkSwitch-4

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PI-7459-090215

IFON

IBDSRC

tFON

IBD

Logic BD

Logic ED

BD Ground

Figure 9. Base Drive Waveforms.

If the output does not reach V

OUT(UVP) during this time then the

controller will shutdown and restart.

V

OUT(UVP) value depends on the set output voltage (VOUT(CV)) and the

feedback UVP ratio:

VV

G

OUTUVP

OUTCVFBUVP

#

=

^^

^

hh

h

Easy Start (LNK4114D, LNK4214D, LNK4115D, LNK4215D)

The Easy Start feature guarantees start-up into large output

capacitances and allows the output voltage to work down the CC

chimney close to OV.

The Easy Start feature uses the BJT emitter current (equal to the

primary current) to charge the supply capacitor C

VCC via an additional

Schottky diode.

This only occurs when the supply voltage has fallen below V

VCCES and

is achieved by altering the sequencing of EMITTER DRIVE pin switching.

If the supply voltage is below V

VCC(ES), and when the base has received

enough charge, the EMITTER DRIVE pin is released at the same time

as the BASE DRIVE pin.

This allows the BJT emitter voltage to rise until the Schottky diode

conducts. Emitter current then charges the C

VCC until the BJT is

turned off by the BASE DRIVE pin being pulled low.

If the supply voltage is above V

VCC(ES), then Easy Start has no effect

on the operation of the controller.

Note V

VCC(ES) = 6 V for LNK4114D and LNK4214D, VVCC(ES) = 10 V for

LNK43x3S, LNK43x3D, LNK4115D and LNK4215D during N

STARTUP cycles,

after which it reduces to 6 V.

Over-Temperature Protection

Temperature protection is internal to LinkSwitch-4. The sensor

measures the junction temperature T

J, which is the hottest part of

LinkSwitch-4.

At temperatures T

J ~ 140 °C, LinkSwitch-4 will shutdown and remain

in this state until a temperature of T

J ~ 70 °C is reached. Whereby

LinkSwitch-4 will power-up in the normal sequence.

Figure 9b. Base Drive Waveforms – Easy Start mode of Operation.

PI-7674-090215

IFON

IBDSRC

IBD

VCC

Logic BD

Logic ED

BD Ground

CVCC Recharge Current

tFON