LT1172MJ8 Linear Technology, LT1172MJ8 Datasheet - Page 4

• Manufacturer Part Number: LT1172MJ8
• Description: SP-SWREG/Monolithic, 100kHz 5A 2.5A And 1.25A High Efficiency Switching Regulato
• Manufacturer: Linear Technology

LT1 170/LT1 171/LT1172
perature range, otherwise specifications are at T
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
BV
V
I
f
DC
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: Minimum effective switch “on” time for the LT1170/71/72 (in current
limit only) is 0.6 s. This limits the maximum safe input voltage during an
output shorted condition. Buck mode and inverting mode input voltage during
an output shorted condition is limited to:
V
buck and inverting mode
R = Inductor DC resistance
I
Vf = Output catch diode forward voltage at I
t = 0.6 s, f = 100kHz switching frequency
Maximum input voltage can be increased by increasing R or Vf.
External current limiting such as that shown in AN19, Figure 39, will
provide protection up to the full supply voltage rating. C1 in Figure 39
should be reduced to 200pF.
4
LIM
L
SAT
IN
I
I
SW
= 10A for LT1170, 5A for LT1171, and 2.5A for LT1172
IN
MAX
(max, output shorted) = 15V +
Flyback Amplifier Source
and Sink Current
Output Switch Breakdown
Voltage
Output Switch
“On” Resistance (Note 3)
Control Voltage to Switch
Current Transconductance
Switch Current Limit
Supply Current Increase
During Switch On-Time
Switching Frequency
Maximum Switch Duty Cycle
Shutdown Mode
Supply Current
Shutdown Mode
Threshold Voltage
Flyback Sense Delay Time (Note 5)
(LT1170)
(LT1171)
(LT1172)
(R)(I
(t)(f)
L
) + Vf
L
CONDITIONS
V
I
3V V
I
LT1170
LT1171
LT1172
LT1170
LT1171
LT1172
Duty Cycle = 50%
Duty Cycle = 50%
Duty Cycle = 80% (Note 4)
Duty Cycle = 50%
Duty Cycle = 50%
Duty Cycle = 80% (Note 4)
Duty Cycle = 50%
Duty Cycle = 50%
Duty Cycle = 80% (Note 4)
3V V
V
3V V
FB
SW
C
C
= 0.6V
= 0.05V
= 50 A
= 1.5mA
A
IN
IN
IN
= 25 C. V
V
V
V
MAX
MAX
MAX
,
The
IN
Source
Sink
LT1170/LT1171/LT1172
LT1170HV/LT1171HV/LT1172HV
LT1172S8
= 15V, V
denotes the specifications which apply over the full operating tem-
Transformer designs will tolerate much higher input voltages because
leakage inductance limits rate of rise of current in the switch. These
designs must be evaluated individually to assure that current limit is well
controlled up to maximum input voltage.
Boost mode designs are never protected against output shorts because
the external catch diode and inductor connect input to output.
Note 3: Measured with V
2A for LT1171, and 1A for LT1172.
Note 4: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current is given by I
I
LT1172.
Note 5: Minimum input voltage for isolated flyback mode is 7V. V
55V for HV grade in fully isolated mode to avoid switch breakdown.
LIM
C
= 0.5V, V
= 1.67 (2 – DC) for the LT1171, and I
FB
= V
T
T
T
T
T
T
J
J
J
J
J
J
REF
25 C
25 C
25 C
25 C
25 C
25 C
, output pin open, unless otherwise noted.
C
in hi clamp, V
LIM
100
MIN
1.25
1.25
1.00
88
85
85
50
2.5
2.5
2.0
FB
15
25
65
75
60
5
5
4
LIM
= 3.33 (2 – DC) for the LT1170,
= 0.8V. I
= 0.833 (2 – DC) for the
0.15
0.30
0.60
TYP
100
100
150
1.5
32
40
90
90
80
25
92
8
4
2
SW
= 4A for LT1170,
MAX
0.24
0.50
1.00
112
115
250
250
300
5.0
5.5
5.0
3.0
3.5
2.5
70
70
10
11
10
35
97
MAX
117012ff
UNITS
mA/A
=
A/V
A/V
A/V
kHz
kHz
mV
mV
%
A
A
V
V
V
A
A
A
A
A
A
A
A
A
A
s