LT1737IGN#PBF Linear Technology, LT1737IGN#PBF Datasheet - Page 22

• Manufacturer Part Number: LT1737IGN#PBF
• Description: IC CNTRLR ISOLATD FLYBACK 16SSOP
• Manufacturer: Linear Technology
• Type: Flybackr

Specifications of LT1737IGN#PBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Frequency - Switching: 50kHz ~ 250kHz
• Voltage - Input: 4.1 ~ 20 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Primary Input Voltage: 20V
• No. Of Outputs: 1
• Output Voltage: 12.1V
• Output Current: 100mA
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Output: -
• Power - Output: -

LT1737
Overall power supply efficiency and output regulation
versus input voltage and load current may be seen in
Figures 9 and 10. Available output current is a function of
input voltage, varying from 650mA with 8V input to
1100mA with 25V input.
In cases when the output switching noise is objectionable,
the optional output L/C filter shown may be added. The
oscilloscope photos in Figure 11 show the dramatic reduc-
tion in output voltage ripple with the optional filter.
Note: It is theoretically possible to extend the input voltage
range of this topology higher by raising the breakdown
voltage ratings on Q1, U2 and M1, while adjusting the
transformer windings as necessary. However this ap-
proach is generally undesirable as the relatively fixed
TYPICAL APPLICATIO S
22
5.25
5.00
4.75
90
80
70
60
50
40
30
20
0.01
0
Figure 10. Output Regulation
Figure 9. Efficiency vs I
250
V
IN
= 8V
500
V
I
IN
LOAD
I
LOAD
= 8V
0.1
V
(mA)
IN
(A)
V
750
IN
= 15V
= 25V
V
U
IN
V
1000
= 15V
IN
LOAD
= 25V
1737 F10
1737 F09
1250
1
supply current required by the LT1737 generates more
and more wasted heat in linear regulator U2 as input
voltage is increased. The LT1725, a close “cousin” of the
LT1737 is recommended in such instances.
The LT1725 is very similar to the LT1737, but it contains
an integral wide hysteresis undervoltage lockout (UVLO)
circuit that monitors the V
conjunction with a 3-winding transformer to provide both
device power and output voltage feedback information,
this allows for a “trickle charge” start-up from an input
voltage of up to hundreds of volts. The LT1725 is thus well
suited to operate from “telecom” input voltages of 48V to
72V, or even offline inputs up to several hundred volts! See
the LT1725 data sheet for further information.
AC COUPLED
AC COUPLED
50mV/DIV
50mV/DIV
V
I
20MHz BANDWIDTH LIMITED
V
I
20MHz BANDWIDTH LIMITED
LOAD
LOAD
IN
IN
= 15V
= 15V
= 900mA
= 900mA
Without L/C Filter
With L/C Filter
Figure 11
1µs/DIV
1µs/DIV
CC
voltage. When used in
1737 F11b
1737 F11a
1737fa