Datasheet

2
LT1270A/LT1270
1270afc
WU
U
PACKAGE
/
O
RDER I FOR ATIO
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
V
REF
Reference Voltage Measured at Feedback Pin 1.224 1.244 1.264 V
V
C
= 0.8V ● 1.214 1.244 1.274 V
I
B
Feedback Input Current V
FB
= V
REF
350 750 nA
1100 nA
gm Error Amplifier ∆l
C
= ±25µA 3000 4400 6000 µmho
Transconductance
● 2400 7000 µmho
Error Amplifier Source of V
C
= 1.5V 150 200 350 µA
Sink Current ● 120 400 µA
Error Amplifier Clamp Voltage Hi Clamp, V
FB
= 1V 1.80 2.30 V
Lo Clamp, V
FB
= 1.5V 0.25 0.38 0.52 V
Reference Voltage Line Regulation 3V ≤ V
IN
≤ V
MAX
, V
C
= 0.8V ● 0.03 %/V
A
V
Error Amplifier Voltage Gain 0.9V ≤ V
C
≤ 1.4V 500 800 V/V
Minimum Input Voltage ● 2.8 3.0 V
I
Q
Supply Current 3V ≤ V
IN
≤ V
MAX
, V
C
= 0.6V 7 10 mA
Control Pin Threshold Duty Cycle = 0 0.70 0.90 1.08 V
● 0.50 1.25 V
Normal/Flyback Threshold 0.40 0.45 0.54 V
on Feedback Pin
V
FB
Flyback Reference Voltage I
FB
= 50µA 15.0 16.3 17.6 V
● 14.0 18.0 V
V
FB
Change in Flyback Reference 0.05 ≤ I
FB
≤ 1mA 4.5 6.8 8.5 V
Voltage
Flyback Reference Voltage I
FB
= 50µA 0.01 0.03 %/V
Line Regulation 3V ≤ V
IN
≤ V
MAX
Flyback Amplifier ∆l
C
= ±10µA 150 300 650 µmho
Transconductance (gm)
Flyback Amplifier Source V
C
= 0.6V Source ● 15 32 70 µA
and Sink Current I
FB
= 50µA Sink ● 25 40 70 µA
BV Output Switch Breakdown 3V ≤ V
IN
≤ V
MAX
● 60 75 V
Voltage I
SW
= 1.5mA
V
SAT
Output Switch ON T
J
≤ 100°C 0.12 0.18 Ω
Resistance (Note 2, 4) T
J
≤ 125°C 0.22 Ω
Control Voltage to Switch 12 A/V
Current Transconductance
LIM
Switch Current Limit (LT1270) Duty Cycle = 50%, T
J
≤ 100°C ● 816A
(Note 4) Duty Cycle = 80%, T
J
≤ 100°C ● 614A
A
U
G
W
A
W
U
W
ARB
S
O
LU
T
EXI T
I
S
Supply Voltage ....................................................... 30V
Switch Output Voltage ............................................ 60V
Feedback Pin Voltage (Transient, 1ms) ................ ±15V
Operating Junction Temperature Range
LT1270AC/LT1270C (Oper.)................ 0°C to 125°C
LT1270AC/LT1270C (Short-Ckt) ......... 0°C to 140°C
Storage Temperature Range ................ –65°c to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER PART
NUMBER
LT1270CT
LT1270ACT
T PACKAGE
5-LEAD PLASTIC TO-220
V
IN
V
SW
GND
FB
V
C
FRONT VIEW
TAB
IS
GND
5
4
3
2
1
T
JMAX
= 100°C, θ
JA
= 2°C/W, θ
JA
= 50°C/W
(Note 1)
Consult LTC Marketing for parts specified with wider operating temperature ranges.