LinkSwitch-HP
Remote On/Off and Fast AC Reset
At power-up the current out of the FEEDBACK pin has to
exceed the line undervoltage turn-on threshold (brown-in)
current IFB(UVREF) = -250 mA (typ.) before switching is enabled.
During normal operation switching is disabled if the FEEDBACK
pin current falls below the line undervoltage turn-off threshold
(brown-out) current IFB(UVOFF) = -100 mA (typ.) for at least 8
consecutive switching cycles. After switching has ended, the
device enters auto-restart. The applicable auto-restart off-
period tAR(OFF)1 = 150 ms (typ.).
The PROGRAM pin can be used to turn on/off the device
remotely. If the voltage on the pin is set to 1.35 V externally, the
device stops switching. After releasing the PROGRAM pin the
PROGRAM pin device commences switching when the voltage
drops below 0.535 V.
500
PROGRAM Pin Resistor Value
450
124 kΩ
78.7 kΩ
400
52.3 kΩ
34.8 kΩ
D
350
VSEC
NS
VBUS
23.2 kΩ
15.0 kΩ
10.0 kΩ
300
CO
VO
NP
250
200
150
100
50
VAUX
NA
RFB1
D
S
BP
T1
CONTROL
FB
0
U1
1
10
100
PD CP
PROGRAM Pin Capacitor Value (nF)
RFB2
VFB
Figure 6. Optional Shutdown Time Extension Programming.
The PROGRAM pin can also be used to reset the device latch
after a latching OVP or OTP event. If the voltage on the pin is
set to 3.4 V externally, the device latch is reset. Once the
voltage drops below 0.535 V, device will start switching.
PI-6837-120312
Figure 8. Indirect High-Voltage Bus Sensing.
Switching is also stopped if the FEEDBACK pin current exceeds
the line overvoltage threshold current IFB(OV) = -1.15 mA (typ.) for
at least 2 consecutive switching cycles.
110
100
90
Current Limit Compensation Over Line
The high-voltage bus is sensed by means of measuring the
current out of the FEEDBACK pin during the MOSFET on-time.
To limit available overload power over line the set current limit is
compensated as shown in Figure 7. The compensation is
disabled at peak currents below 50% of the set current limit,
and is re-enabled at 62.5% of the set current limit.
80
70
Soft-Start
A digital soft-start is implemented to reduce component stress
at power supply start-up. The internal reference voltage will ramp
up to 2 V during tSOFT (typ. 15 ms) at start-up. The loop will
typically close (output reaches regulation) during this time to
ensure smooth output voltage rise.
-150
-300
-450
-600
-750
-900
-1050 -1200
FEEDBACK Pin Current During MOSFET On-Time
Figure 7. Current Limit Compensation Over Line.
Fault Filter
This is the digital filter to handle all the fault conditions including
line overvoltage, line undervoltage, output overvoltage, and
output undervoltage, thermal shutdown as well as package
level fault (pin open-circuit or pin-to-pin short-circuit).
High-Voltage Bus Sensing
LinkSwitch-HP senses indirectly the HV voltage bus VBUS during
the power MOSFET on-time by monitoring the current flowing
out of the FEEDBACK pin. During the MOSFET on-time the
voltage across the auxiliary winding is proportional to the voltage
across the input winding. The current flowing through resistor
RFB1 (see Figure 8) is therefore representing VBUS. Indirect line
sensing minimizes power dissipation and is used for line UV or
line OV protection and current limit compensation over line.
Transconductance Amplifier
The controller uses a high gain (typ. 70 dB) transconductance
amplifier to ensure exceptional output regulation.
5
Rev. E 06/15
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