LT1950 Linear Technology, LT1950 Datasheet - Page 8

• Manufacturer Part Number: LT1950
• Description: Single Switch PWM Controller
• Manufacturer: Linear Technology

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BLOCK DIAGRA
LT1950
The LT1950 is a constant frequency, current mode con-
troller for DC/DC forward, boost, flyback and SEPIC con-
verter applications. The Block Diagram in Figure 1 shows
all of the key functions of the IC.
In normal operation, a V
internal switcher at the BOOST pin to generate a separate
8
OPERATIO
SLOPE
SHDN
SYNC
R
OSC
7
4
3
5
U
FB
2
1.23V
3 A
+
IN
W
voltage as low as 3V allows an
+
–
1.23V
ERROR AMPLIFIER
VOLTAGE GAIN = 85dB
–
V
15
IN
1.32V
(TYPICAL 200kHz)
OSC
COMP
(100-500)khz
2.5V
(SOURCE 2.5mA
EXTERNALLY)
V
INTERNAL +
EXTERNAL
SUPPLY
(V
U/V LOCKOUT
1
REF
IN
V
IN2
) (2.6V)
=
V
REF
6
Figure 1. LT1950 Block Diagram
RAMP
(105/V
V
SEC
16
SEC
GND
8
)%
–
+
BOOST
SLOPE COMP
MAX DC
CLAMP
14
PGND
0mV – >100mV
SWITCHING PREREGULATOR
(125mA CURRENT LIMIT)
11V supply at V
inductor, diode and capacitor. Since V
output driver of the IC, this architecture achieves high
GATE drive for an external N-channel power MOSFET even
though V
reduces MOSFET R
CURRENT
SENSE
FIXED OFF TIME
CMP
S
R
–
BLANKING
IN
voltage is very low. High GATE drive capability
+
ENABLE
U/V LOCKOUT
Q
(V
BLANK
IN2
IN2
9
DISABLE
) (8V)
–
+
using a small surface mount external
DRIVER
1A
DS(ON)
13V
–
125mV
+
–
+
–
for improved efficiency,
11V
8V
+
BLANKING
OVERRIDE
CMP
V
1950 BD
11
IN2
10
12
13
IN2
GATE
PGND
I
SENSE
supplies the
sn1950 1950fs