LinkSwitch-4
If the output does not reach VOUT(UVP) during this time then the
controller will shutdown and restart.
This allows the BJT emitter voltage to rise until the Schottky diode
conducts. Emitter current then charges the CVCC until the BJT is
turned off by the BASE DRIVE pin being pulled low.
VOUT(UVP) value depends on the set output voltage (VOUT(CV)) and the
feedback UVP ratio:
If the supply voltage is above VVCC(ES), then Easy Start has no effect
on the operation of the controller.
VOUT UVP = V
# G
^
h
^
h
^
h
OUT CV
FB UVP
Note VVCC(ES) = 6 V for LNK4114D and LNK4214D, VVCC(ES) = 10 V for
LNK43x3S, LNK43x3D, LNK4115D and LNK4215D during NSTARTUP cycles,
after which it reduces to 6 V.
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.
Over-Temperature Protection
Temperature protection is internal to LinkSwitch-4. The sensor
measures the junction temperature TJ, which is the hottest part of
LinkSwitch-4.
The Easy Start feature uses the BJT emitter current (equal to the
primary current) to charge the supply capacitor CVCC via an additional
Schottky diode.
At temperatures TJ ~ 140 °C, LinkSwitch-4 will shutdown and remain
in this state until a temperature of TJ ~ 70 °C is reached. Whereby
LinkSwitch-4 will power-up in the normal sequence.
This only occurs when the supply voltage has fallen below VVCCES and
is achieved by altering the sequencing of EMITTER DRIVE pin switching.
If the supply voltage is below VVCC(ES), and when the base has received
enough charge, the EMITTER DRIVE pin is released at the same time
as the BASE DRIVE pin.
ꢍFꢇꢈ
ꢁFꢇꢈ
ꢁꢉꢊ
ꢁꢉꢊꢋRꢌ
ꢎꢏꢐꢑꢒ ꢉꢊ
ꢎꢏꢐꢑꢒ ꢓꢊ
ꢉꢊ ꢔꢕꢏꢖꢗꢘ
ꢀꢁꢂꢃꢄ5ꢅꢂ0ꢅ0ꢆ15
Figure 9. Base Drive Waveforms.
ꢎꢍꢍ
ꢜFꢈꢉ
ꢁFꢈꢉ
ꢁꢊꢋ
ꢁꢊꢋꢌRꢍ
ꢏꢐꢑꢒꢓ ꢊꢋ
ꢏꢐꢑꢒꢓ ꢔꢋ
ꢊꢋ ꢕꢖꢐꢗꢘꢙ
ꢍꢎꢍꢍ Reꢓꢚꢛꢖꢑe ꢍꢗꢖꢖeꢘꢜ
ꢀꢁꢂꢃꢄꢃꢅꢂ0ꢆ0ꢇ15
Figure 9b. Base Drive Waveforms – Easy Start mode of Operation.
7
Rev. F 05/18
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