lt1373hv Linear Technology Corporation, lt1373hv Datasheet - Page 10

• Manufacturer Part Number: lt1373hv
• Description: 250khz Low Supply Current High Efficiency 1.5a Switching Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT1373
To prevent irregular switching, V
kept below 50mV
maximum output load current and will also be increased if
poor quality (high ESR) output capacitors are used. The
addition of a 0.001 F capacitor on the V
switching frequency ripple to only a few millivolts. A low
value for R
margin may be inadequate.
Switch Node Considerations
For maximum efficiency, switch rise and fall time are made
as short as possible. To prevent radiation and high fre-
quency resonance problems, proper layout of the compo-
nents connected to the switch node is essential. B field
(magnetic) radiation is minimized by keeping output di-
ode, switch pin and output bypass capacitor leads as short
as possible. E field radiation is kept low by minimizing the
length and area of all traces connected to the switch pin.
A ground plane should always be used under the switcher
circuitry to prevent interplane coupling.
TYPICAL APPLICATIONS
10
OFF
V
g
R
V
m
RIPPLE
OUT
C
ON
+
Positive-to-Negative Converter with Direct Feedback
= series resistor on V
= error amplifier transconductance ( 375 mho)
4
= DC output voltage
C1
22 F
S/S
C
= output ripple (V
V
C
will also reduce V
2.7V TO 16V
1
R1
5k
LT1373
C2
0.01 F
V
V
IN
IN
5
P-P
GND
U
V
NFB
SW
. Worst-case V
6, 7
*COILTRONICS CTX20-2 [phone]
8
3
U
C
D2
P6KE-15A
D3
1N4148
P-P
pin
†
C
0.75A
MAX I
I
0.3A
0.5A
OUT
MBRS130LT3
pin ripple, but loop phase
)
OUT
C
U
2
1
V
3V
5V
9V
W
•
IN
C
pin ripple should be
T1*
pin ripple occurs at
D1
•
4
3
N
C
+
pin reduces
R2
2.55k
1%
R3
2.49k
1%
U
C3
47 F
–V
–5V
LT1373 • TA03
OUT
†
OFF
The high speed switching current path is shown schemati-
cally in Figure 3. Minimum lead length in this path is
essential to ensure clean switching and low EMI. The path
including the switch, output diode and output capacitor is
the only one containing nanosecond rise and fall times.
Keep this path as short as possible.
More Help
For more detailed information on switching regulator
circuits, please see AN19. Linear Technology also offers a
computer software program, SwitcherCAD
designing switching converters. In addition, our applica-
tions department is always ready to lend a helping hand.
SwitcherCAD is a trademark of Linear Technology Corporation.
V
+
IN
Dual Output Flyback Converter with Overvoltage Protection
ON
275k
C1
100 F
1%
R2
4
S/S
V
FB
C
1
2
R3
5k
LT1373
L1
C2
0.01 F
4.75V TO 13V
SWITCH
NODE
*DALE LPE-4841-100MB [phone]
GND
V
V
V
NFB
IN
IN
SW
5
6, 7
8
3
CIRCULATING
FREQUENCY
Figure 3
PATH
HIGH
1N4148
P6KE-20A
302.6k
1%
R1
2, 3
6, 7
•
T1*
MBRS140T3
MBRS140T3
•
•
5
4
8
1
TM
, to assist in
+
+
LOAD
R4
12.4k
1%
R5
2.49k
1%
C3
47 F
C4
47 F
LT1373 • F03
LT1373 • TA04
V
OUT
V
15V
–V
–15V
OUT
OUT