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X-11181-002 Datasheet(PDF) 6 Page - Linear Technology

Part No. X-11181-002
Description  Isolated No Opto-Coupler Flyback Controller
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LT3798
6
3798f
CTRL1, CTRL2, CTRL3 (Pin 1, Pin 2, Pin 3): Current
Output Adjustment Pins. These pins control the output
current. The lowest value out of the three CTRL inputs is
compared to negative input of the operational amplifier.
VREF (Pin 4): Voltage Reference Output Pin. Typically 2V.
This pin drives a resistor divider for the CTRL pin, either
for analog dimming or for temperature limit/compensation
of output load. Can supply up to 200μA.
OVP (Pin 5): Overvoltage Protection. This pin accepts a
DC voltage to compare to the sample and hold’s voltage
output information. When output voltage information is
above the OVP, the part divides the minimum switching
frequency by 8, around 500Hz. This protects devices con-
nected to the output. This also allows the part to operate
with very little power consumption with no load to meet
energy star requirements.
VC (Pin 6): Compensation Pin for Internal Error Amplifier.
Connect a series RC from this pin to ground to compensate
the switching regulator. A 100pF capacitor in parallel helps
eliminate noise.
COMP+, COMP(Pin 7, Pin 8): Compensation Pins for
Internal Error Amplifier. Connect a capacitor between these
two pins to compensate the internal feedback loop.
FB (Pin 9): Voltage Loop Feedback Pin. FB is used to
regulate the output voltage by sampling the third wind-
ing. If the converter is used in current mode, the FB pin
will normally be at a voltage level lower than 1.25V, and
will reach the steady state of 1.25V if it detects an open
output condition.
DCM (Pin 10): Discontinuous Conduction Mode Detection
Pin. Connect a capacitor and resistor in series with this
pin to the third winding.
VIN (Pin 11): Input Voltage. This pin supplies current to
the internal start-up circuitry and to the INTVCC LDO. This
pin must be locally bypassed with a capacitor. A 42V shunt
regulator is internally connected to this pin.
EN/UVLO (Pin 12): Enable/Undervoltage Lockout. A resis-
tor divider connected to VIN is tied to this pin to program
the minimum input voltage at which the LT3798 will turn
on. When below 1.25V, the part will draw 60μA with most
of the internal circuitry disabled and a 10μA hysteresis
current will be pulled out of the EN/UVLO pin. When above
1.25V, the part will be enabled and begin to switch and the
10μA hysteresis current is turned off.
INTVCC (Pin 13): Regulated Supply for Internal Loads
and GATE Driver. Supplied from VIN and regulates to 10V
(typical). INTVCC must be bypassed with a 4.7μF capacitor
placed close to the pin.
PIN FUNCTIONS
Power Factor vs Input Voltage
Efficiency vs Input Voltage
VIN (VAC)
90
0.90
0.92
0.91
0.95
0.96
0.97
0.98
0.99
1.00
150
210
190
230
0.93
0.94
130
110
170
250 270
3798 G15
PAGE 17 SCHEMATIC:
UNIVERSAL
VIN (VAC)
90
60
70
80
90
100
150
210
190
230
130
110
170
250 270
3798 G16
PAGE 17 SCHEMATIC:
UNIVERSAL
TYPICAL PERFORMANCE CHARACTERISTICS T
A = 25°C, unless otherwise noted.




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