LT1725IS Linear Technology, LT1725IS Datasheet - Page 24

• Manufacturer Part Number: LT1725IS
• Description: IC CNTRLR ISOLATD FLYBACK 16SOIC
• Manufacturer: Linear Technology
• Type: Flybackr

Specifications of LT1725IS

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Frequency - Switching: 50kHz ~ 250kHz
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Voltage - Output: -
• Voltage - Input: -
• Power - Output: -

LT1725
TELECOM 48V TO ISOLATED 5V APPLICATION
The design in Figure 10 accepts an input voltage in the
range of 36V to 72V and outputs an isolated 5V at up to 2A.
Transformer T1 is available as a Coiltronics CTX02-14989.
Capacitor C7 sets the switching frequency at approxi-
mately 275kHz. Optimal load compensation for the trans-
former and secondary circuit components is set by resistor
TYPICAL APPLICATIO S
24
35.7k
3.01k
1%
1%
R3
R4
5.25
5.00
4.75
0
C6
1nF
8
7
Application Regulation
FB
V
OSCAP
0.5
C
C9
100pF
V
V
IN
IN
6
3V
= 36V
= 72V
C7
47pF
SFST
I
OUT
LOAD
9
R13
820k
R14
33k
1.0
3
(A)
UVLO
t
V
ON
IN
10
14
R5
51k
= 48V
U
ENDLY
1.5
13
R6
51k
1725 F10b
BAS16
MENAB
LT1725
Figure 10. 48V to Isolated 5V Converter
D2
2.0
12
R7
51k
+
R
OCMP
R10
22Ω
C1
15µF
4
R8
2.7k
V
R
CC
CMPC
15
R1
47k
5
C8
0.1µF
C10
1µF
SGND
R8. Output voltage regulation and overall efficiency are
shown in the accompanying graphs. Efficiency is shown
both with and without the R11 preload. The resistor divider
formed by R13 and R14 sets the undervoltage lockout
threshold at about 32V, with a hysteresis band of about 2V.
The soft-start and 3V
V
11
IN
I
SENSE
PGND
C2
1.5µF
GATE
1
16
2
90
80
70
60
50
40
30
20
R12
68Ω
0.01
C4
150pF
V
IN
= 48V
CTX02-14989
6
1
2
4
WITHOUT R11
Application Efficiency
M1
IRF620
T1
R2
0.18Ω
1725 F10a
OUT
PRELOAD
0.1
9
11
10
12
I
features are unused as shown.
LOAD
18Ω
R9
12CWQ06
(A)
WITH R11
PRELOAD
D1
470pF
1
C5
+
1725 F10c
C3
150µF
10
R11
51Ω
1W
V
5V
OUT
1725fa