Datasheet

3
LT1270A/LT1270
1270afc
E
LECTR
IC
AL C CHARA TERIST
ICS
The ● denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, switch pin open, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
LIM
Switch Current Limit (LT1270A) Duty Cycle = 50%, T
J
≤ 100°C ● 10.0 16.0 A
(Note 4) Duty Cycle = 80%, T
J
≤ 100°C ● 7.5 14.0 A
∆I
IN
Supply Current Increase 25 40 mA/A
∆I
SW
During Switch-ON Time
f Switching Frequency 50 60 70 kHz
● 50 70 kHz
DC
MAX
Maximum Switch Duty Cycle 80 92 95 %
Flyback Sense Delay Time 1.5 µs
Shutdown Mode Supply Current 3V ≤ V
IN
≤ V
MAX
, V
C
= 0.05V 100 400 µA
Shutdown Mode Threshold Voltage 3V ≤ V
IN
≤ V
MAX
100 150 250 mV
● 50 300 mV
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Measured with V
C
in Hi Clamp, V
FB
= 0.8V.
Note 3: For duty cycles (DC) between 50% and 80%, minimum guaranteed
switch current is given by I
LIM
= 6.67 (1.7 – DC) for the LT1270 and I
LIM
=
8.33 (1.7 – DC) for the LT1270A.
Note 4: Minimum current limit is reduced by 0.5A at 125°C. 100°C test
limits are guaranteed by correlation to 125°C tests.
TYPICAL APPLICATIO S
U
Boost Converter (5V to 12V)
1k
MBR1020
V
IN
V
SW
FB
V
C
GND
LT1270
10.7k
+
55µH*
1µF
1.24k
+
1000µF
25V
5V
12V, 2A
PULSE ENGINEERING #PE-92116
LT1270 • TA05
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Switch Saturation VoltageSwitch Current Limit vs Duty Cycle
DUTY CYCLE (%)
0
SWITCH CURRENT (A)
18
24
80
LT1270 • TA03
12
6
0
20
40
60
100
–55°C
125°C
25°C
SWITCH CURRENT (A)
0
SWITCH SATURATION VOLTAGE (V)
1.2
1.6
8
LT1270 • TA04
0.8
0.4
0
2
4
6
10
T
J
= 25°C
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However,
no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the
interconnection of circuits as described herein will not infringe on existing patent rights.