LT1072
1.25A High Efficiency
Switching Regulator
FEATURES
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DESCRIPTIO
Available in MiniDiP, TO-220, and TO-3 Packages
Wide Input Voltage Range 3V to 60V
Low Quiescent Current—6mA
Internal 1.25A Switch
Very Few External Parts Required
Self-Protected Against Overloads
Operates in Nearly All Switching Topologies
Shutdown Mode Draws Only 50µA Supply Current
Flyback-Regulated Mode has Fully Floating Outputs
Can be Externally Synchronized
The LT
®
1072 is a monolithic high power switching
regulator. It can be operated in all standard switching
configurations including buck, boost, flyback, forward,
inverting and “Cuk”. A high current, high efficiency switch
is included on the die along with all oscillator, control, and
protection circuitry. Integration of all functions allows the
LT1072 to be built in a standard 5-pin TO-3 or TO-220
power package as well as the 8-pin miniDlP. This makes it
extremely easy to use and provides “bust proof” operation
similar to that obtained with 3-pin linear regulators.
The LT1072 operates with supply voltages from 3V to 60V,
and draws only 6mA quiescent current. It can deliver load
power up to 20 watts with no external power devices. By
utilizing current-mode switching techniques, it provides
excellent AC and DC load and line regulation.
The LT1072 has many unique features not found even on
the vastly more difficult to use low power control chips
presently available. It uses an adaptive anti-sat switch
drive to allow very wide ranging load currents with no loss
in efficiency. An externally activated shutdown mode
reduces total supply current to 50µA typical for standby
operation. Totally isolated and regulated outputs can be
generated by using the optional “flyback regulation mode”
built into the LT1072, without the need for optocouplers or
extra transformer windings.
APPLICATIO S
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Logic Supply 5V at 2.5A
5V Logic to
±15V
Op Amp Supply
Offline Converter up to 50W
Battery Upconverter
Power lnverter (+ to –) or (– to +)
Fully Floating Multiple Outputs
Driver for High Current Supplies
USER NOTE:
This data sheet is only intended to provide specifications, graphs, and a general functional
description of the LT1072. Application circuits are included to show the capability of the LT1072.
A complete design manual (AN-19) should be obtained to assist in developing new designs. This
manual contains a comprehensive discussion of both the LT1070 and the external components used
with it, as well as complete formulas for calculating the values of these components. The manual
can also be used for the LT1072 by factoring in the lower switch current rating.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
5V
220µH**
Boost Converter (5V to 12V)
25
Maximum Output Power*
V
IN
V
SW
POWER (W)
20
BUCK-BOOST
V
O
= 30V
BOOST
10
FLYBACK
ISOLATED
C3
25µF*
+
–
LT1072
10.7k
GND
V
C
1k
FB
12V, 0.25A
15
+
1µF
–
*REQUIRED IF INPUT LEADS
≥
2”
**PULSE ENGINEERING 52626
1.24k
+
470µF
–
5
BUCK-BOOST
V
O
= 5V
0
0
10
30
20
INPUT VOLTAGE (V)
40
50
LT1072 • TA01
*ROUGH GUIDE ONLY. BUCK MODE P
OUT
= 1A x V
OUT
.
MINIDIP OUTPUT POWER MAY BE LIMITED BY PACKAGE TEMPERATURE
RISE AT HIGH INPUT VOLTAGES OR HIGH DUTY CYCLES
LT1072 • TA02
U
1072fc
U
U
1
LT1072
ABSOLUTE
(Note 1)
AXI U
RATI GS
Note 1:
Minimum switch “on” time for the LT1072 in current limit is
≈
0.7µsec. This limits the maximum input voltage during short-circuit
to
conditions,
in the buck and inverting modes only,
≈
40V. Normal
(unshorted) conditions are not affected. If the LT1072 is being operated in
the buck or inverting mode at high input voltages and short-circuit
conditions are expected, a resistor must be placed in series with the
inductor, as follows:
The value of the resistor is given by:
Supply Voltage
LT1072HV (See Note 1) ......................................... 60V
LT1072 (See Note 1) ............................................. 40V
Switch Output Voltage
LT1072HV ............................................................. 75V
LT1072 .................................................................. 65V
LT1072S8 .............................................................. 60V
Feedback Pin Voltage (Transient, 1ms) .................
±15V
Operating Junction Temperature Range
LT1072HVM, LT1072M
(OBSOLETE)
.... –55°C to 150°C
LT1072HVC, LT1072C (Oper.)* ............0°C to 100°C
LT1072HVC, LT1072C (Sh. Ckt.)* ........0°C to 125°C
LT1072HVI ....................................... –40°C to 125°C
Storage Temperature Range ............... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ............... 300°C
*Includes LT1072S8
PACKAGE/ORDER I FOR ATIO
BOTTOM VIEW
V
SW
1
4
V
IN
2
3
V
C
CASE IS
GND
ORDER PART
NUMBER
LT1072HVMK
LT1072MK
LT1072HVCK
LT1072CK
GND
V
C
FB
NC
1
2
3
4
FB
K PACKAGE
4-LEAD TO-3 METAL CAN
T
JMAX
= 150°C,
θ
JC
= 8°C/W,
θ
JA
= 35°C/W
T
JMAX
= 100°C*,
θ
JC
= 8°C/W,
θ
JA
= 35°C/W
N PACKAGE
8-LEAD PDIP
T
JMAX
= 100°C,
θ
JA
= 130°C/W
OBSOLETE PACKAGE
ORDER PART
NUMBER
V
IN
V
SW
GND
FB
V
C
FRONT VIEW
5
4
3
2
1
LT1072CT
LT1072HVCT
LT1072HVIT
T PACKAGE
5-LEAD TO-220
T
JMAX
= 100°C/W,
θ
JC
= 8°C/W,
θ
JA
= 50°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1072fc
2
U
U
W
W W
U
W
R=
(t) (f) (V
IN
) – V
f
– R
L
I
(LIMIT)
t = Minimum “on” time of LT1072 in current limit,
≈
0.7µs
f = Operating frequency (40kHz)
V
f
= Forward voltage of external catch diode at I
(LIMIT)
I
(LIMIT)
= Current limit of LT1072 (2A)
R
L
= Internal series resistance of inductor
TOP VIEW
8
7
6
5
TOP VIEW
E2
V
SW
E1
V
IN
GND
V
C
FB
NC
1
2
3
4
8
7
6
5
ORDER PART
NUMBER
E2
V
SW
E1
V
IN
LT1072CN8
LT1072CS8
S8 PART
MARKING
1072
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 130°C/W
J PACKAGE
8-LEAD CERAMIC DIP
T
JMAX
= 150°C,
θ
JA
= 100°C/W
LT1072MJ8
LT1072CJ8
OBSOLETE PACKAGE
Consider the S8 or N8 Packages for Alternate Source
TOP VIEW
NC
NC
GND
V
C
FB
NC
NC
NC
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
NC
NC
E2
V
SW
E1
V
IN
NC
NC
ORDER PART
NUMBER
LT1072CSW
SW PACKAGE
16-LEAD PLASTIC SO WIDE
T
JMAX
= 100°C,
θ
JC
= 130°C/W
LT1072 • POI01
LT1072
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REF
I
B
gm
PARAMETER
Reference Voltage
Feedback Input Current
Error Amplifier
Transconductance
Error Amplifier Source or
Sink Current
Error Amplifier Clamp
Voltage
Reference Voltage Line
Regulation
A
V
I
Q
Error Amplifier Voltage Gain
Minimum Input Voltage
Supply Current
Control Pin Threshold
Normal/Flyback Threshold on Feedback Pin
V
FB
Flyback Reference Voltage
Change in Flyback Reference Voltage
Flyback Reference Voltage
Line Regulation
Flyback Amplifier Transconductance (gm)
Flyback Amplifier Source
and Sink Current
BV
Output Switch Breakdown
Voltage
Output Switch ON Resistance (Note 2)
The
●
denotes specifications which apply over the full operating
temperature range. Unless otherwise specified, V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open.
CONDITlONS
Measured at Feedback Pin
V
C
= 0.8V
V
FB
= V
REF
●
●
MIN
1.224
1.214
TYP
1.244
1.244
350
MAX
1.264
1.274
750
1100
6000
7000
350
400
2.3
0.52
0.03
UNITS
V
V
nA
nA
µmho
µmho
µA
µA
V
V
%/V
%/V
V/V
V
mA
V
V
V
V
V
V
%/V
%/V
µmho
µA
µA
V
V
V
∆I
C
=
±25µA
●
3000
2400
150
120
1.8
0.25
4400
200
V
C
= 1.5V
●
Hi Clamp, V
FB
= 1V
Lo Clamp, V
FB
= 1.5V
3V
≤
V
IN
≤
V
MAX
V
C
= 0.8V
0.9V
≤
V
C
≤
1.4V
●
●
0.38
500
800
2.6
6
3.0
9
1.08
1.25
0.54
17.6
18
8.5
0.03
650
70
70
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.6V
Duty Cycle = 0
●
0.8
0.6
0.4
15
14
4.5
0.9
0.45
16.3
6.8
0.01
l
FB
= 50µA
●
0.05
≤
I
FB
≤
1mA
l
FB
= 50µA
3V
≤
V
IN
≤
V
MAX
(Note 4)
∆I
C
=
±10µA
V
C
= 0.6V Source
I
FB
= 50µA Sink
3V
≤
V
IN
≤
V
MAX
I
SW
= 1.5mA
I
SW
= 1.25A
Duty Cycle = 50%
T
J
≥
25°C
Duty Cycle = 50%
T
J
< 25°C
Duty Cycle = 80% (Note 3)
LT1072
LT1072HV
LT1072S8
●
●
●
●
●
●
150
15
25
65
75
60
300
32
40
90
90
80
0.6
2
V
SAT
I
LIM
1
3
3.5
2.5
Ω
A/V
A
A
A
mA/A
kHz
kHz
%
µs
µA
mV
mV
Control Voltage to Switch Current Transconductance
Switch Current Limit
●
●
●
1.25
1.25
1
25
35
33
90
40
92
1.5
100
100
50
150
∆I
IN
∆I
SW
f
DC (max)
Supply Current Increase
During Switch ON Time
Switching Frequency
●
35
45
47
97
250
250
300
Maximum Switch Duty Cycle
Flyback Sense Delay Time
Shutdown Mode
Supply Current
Shutdown Mode
Threshold Voltage
3V
≤
V
IN
≤
V
MAX
V
C
= 0.05V
3V
≤
V
IN
≤
V
MAX
●
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
= 0.833 (2 – DC).
Note 4:
V
MAX
= 55V for LT1072HV to avoid switch breakdown.
1072fc
3
LT1072
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Current Limit vs Duty Cycle
4
96
95
SWITCH CURRENT (A)
3
DUTY CYCLE (%)
94
93
92
91
0
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
LT1072 • TPC01
–55°C
2
125°C
1
25°C
TIME (µs)
LT1072 • TPC02
Minimum Input Voltage
2.9
SWITCH SATURATION VOLTAGE (V)
1.6
MINIMUM INPUT VOLTAGE (V)
2.8
2.7
2.6
SWITCH CURRENT = 1.25A
100°C
1.0
0.8
0.6
0.4
0.2
0
0
0.25 0.5 0.75 1 1.25 1.5 1.75
SWITCH CURRENT (A)
2
25°C
–55°C
FLYBACK VOLTAGE (V)
SWITCH CURRENT = 0A
2.5
2.4
2.3
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC04
Line Regulation
5
REFERENCE VOLTAGE CHANGE (mV)
4
REFERENCE VOLTAGE (V)
3
2
1
0
–1
–2
–3
–4
–5
0
10
T
J
= – 55°C
T
J
= 150°C
T
J
=
25
°
C
FEEDBACK BIAS CURRENT (nA)
30
40
20
INPUT VOLTAGE (V)
4
U W
50
LT1072 • TPC07
Maximum Duty Cycle
2.2
2.0
1.8
1.6
1.4
1.2
Flyback Blanking Time
90
–75 –50 –25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (°C)
1.0
–75 –50 –25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (°C)
LT1072 • TPC03
Switch Saturation Voltage
23
22
150°C
1.2
21
20
19
18
17
16
1.4
Isolated Mode Flyback Reference
Voltage
R
FEEDBACK
= 500Ω
R
FEEDBACK
= 1kΩ
R
FEEDBACK
= 10kΩ
15
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (C°)
LT1072 • TPC06
LT1072 • TPC05
Reference Voltage and Switching
Frequency vs Temperature
1.250
1.248
1.246
1.244
1.242
REFERENCE VOLTAGE
1.240
1.238
1.236
1.234
–75 –50 –25
37
36
35
34
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC08
Feedback Bias Current vs
Temperature
42
800
700
600
500
400
300
200
100
0
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC09
SWITCHING FREQUENCY
41
40
FREQUENCY (kHz)
39
38
60
1072fc
LT1072
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Current* vs Switch Current
80
70
SUPPLY CURRENT (mA)
DRIVER CURRENT (mA)
60
50
40
30
20
10
0
0
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
SWITCH CURRENT (A)
2
15
14
SUPPLY CURRENT (µA)
*AVERAGE LT1072 POWER SUPPLY CURRENT IS
FOUND BY MULTIPLYING DRIVER CURRENT BY
DUTY CYCLE, THEN ADDING QUIESCENT CURRENT
LT1072 • TPC10
Normal/Flyback Mode Threshold
on Feedback Pin
500
490
–24
–22
200
180
480
470
460
450
440
430
420
410
400
–50 –25
0
FEEDBACK PIN CURRENT
(AT THRESHOLD)
FEEDBACK PIN VOLTAGE
(AT THRESHOLD)
–20
–18
–16
–14
–12
–10
–8
–6
–4
25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC13
TRANSCONDUCTANCE (µmho)
FEEDBACK PIN VOLTAGE (mV)
SUPPLY CURRENT (µA)
Shutdown Thresholds
400
350
V
C
PIN VOLTAGE (mV)
300
250
200
VOLTAGE
150
100
50
V
C
VOLTAGE IS REDUCED UNTIL
REGULATOR CURRENT DROPS
BELOW 300µA
–150
–100
–50
CURRENT (OUT OF V
C
PIN)
–400
–350
IDLE SUPPLY CURRENT (mA)
–300
–250
–200
V
C
PIN VOLTAGE (µA)
11
10
9
8
7
6
5
4
3
2
FEEDBACK VOLTAGE (mV)
0
–75 –50 –25
0
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC16
U W
Supply Current vs Input Voltage*
T
J
= 25°C
Supply Current vs Supply Voltage
(Shutdown Mode)
160
140
120
100
V
C
= 50mV
80
60
40
20
V
C
= 0V
0
10
40
30
SUPPLY VOLTAGE (V)
20
50
60
T
J
= 25°C
NOTE THAT THIS CURRENT DOES NOT
13 INCLUDE DRIVER CURRENT, WHICH IS
A FUNCTION OF LOAD CURRENT AND
12 DUTY CYCLE.
90% DUTY CYCLE
11
10
9
8
7
6
5
0
10
0% DUTY CYCLE
30
40
20
INPUT VOLTAGE (V)
50
60
50% DUTY CYCLE
10% DUTY CYCLE
0
*UNDER VERY LOW OUTPUT CURRENT CONDITIONS,
DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH
10% OR LESS
LT1072 • TPC11
LT1072 • TPC12
Shutdown Mode Supply Current
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
10 20 30 40 50 60 70 80 90 100
V
C
PIN VOLTAGE (mV)
LT1072 • TPC14
Error Amplifier Transconductance
G
m
=
∆I
(V
C
PIN)
∆V
(FB PIN)
FEEDBACK PIN CURRENT (µA)
160
140
120
100
80
60
40
20
0
– 55°C
≤
T
J
≤
125°C
T
J
= 150°C
0
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (C°)
LT1072 • TPC15
Idle Supply Current vs
Temperature
V
C
= 0.6V
500
450
400
350
300
250
200
150
100
50
0
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC17
Feedback Pin Clamp Voltage
–55°C
25°C
150°C
V
SUPPLY
= 60V
V
SUPPLY
= 3V
1
–75 –50 –25
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
FEEDBACK CURRENT (mA)
1
LT1072 • TPC18
1072fc
5
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