LinkSwitch-HP
SW
VFB
Fast AC Reset
VPDTHACR 3.40 V
tPD Programmable
Shutdown Delay
VPDI
ID ILIMIT
Remote On/Off
VPDTHRM 1.35 V
VPDTHPDH 1.25 V
tPDST
VPDTHPDL 0.535 V
t1 t2
t3
t4
t5
t6
t7
t8
t9
t10
PI-6692-101713
Figure 10. PROGRAM (PD) Pin Timing Diagram.
OSC
maintains a relatively high output sampling rate while reducing
the average switching frequency to keep the output voltage in
regulation. Switching at 25% of the set current limit reduces the
transformer core flux density significantly. This and the intelligent
MCM operation reduce audible noise well below acceptable levels.
LNK666x has a maximum MCM off-time TMCM(OFF) = 0.5 ms (typ.).
The high minimum output sampling rate provides excellent
transient load response from 0% to 50% or 100% of nominal
load while offering typically below 100 mW no-load input power.
This is an adjustable frequency oscillator. Based on error
voltage, the frequency will adjust from 32 kHz at light load to
132 kHz at heavy load. The oscillator employes 5 kHz
frequency jitter to reduce EMI levels.
Current Limit Comparator
This is a high-speed current limit comparator. It compares the
current from the power MOSFET to the internal current reference.
Once the current reaches the threshold the MOSFET on-cycle
is terminated.
LNK67xx has a maximum MCM off-time TMCM(OFF) = 4 ms (typ.).
The lower minimum output sampling rate enables designs
below 30 mW no-load input power while providing fair transient
load performance for load steps from 0% to 50% or 100% of
nominal load.
Multi-Cycle Modulation (MCM)
When voltage on COMPENSATION pin reaches VC(MCM) (about
1.25 V) the peak drain current is reduced to 25% of programmed
value and the switching frequency approaches fMCM = 32 kHz
(typical). During MCM operation the controller intelligently
7
Rev. E 06/15
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