LT1072
1.25A High Efficiency
Switching Regulator
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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
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APPLICATIO S
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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.
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.
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.
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TYPICAL APPLICATIO
Boost Converter (5V to 12V)
5V
20
VSW
12V, 0.25A
LT1072
10.7k
GND
FB
VC
1k
1µF
+
–
*REQUIRED IF INPUT LEADS ≥ 2”
**PULSE ENGINEERING 52626
1.24k
+
470µF
–
POWER (W)
+
–
25
220µH**
VIN
C3
25µF*
Maximum Output Power*
BUCK-BOOST
VO = 30V
15
BOOST
10
FLYBACK
ISOLATED
5
BUCK-BOOST
VO = 5V
0
LT1072 • TA01
0
10
30
20
INPUT VOLTAGE (V)
40
50
*ROUGH GUIDE ONLY. BUCK MODE POUT = 1A x VOUT.
MINIDIP OUTPUT POWER MAY BE LIMITED BY PACKAGE TEMPERATURE
RISE AT HIGH INPUT VOLTAGES OR HIGH DUTY CYCLES
LT1072 • TA02
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LT1072
W W
W
AXI U
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ABSOLUTE
RATI GS
(Note 1)
Note 1: Minimum switch “on” time for the LT1072 in current limit is
≈ 0.7µsec. This limits the maximum input voltage during short-circuit
conditions, in the buck and inverting modes only,to ≈ 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
R=
(t) (f) (VIN) – Vf
– RL
I(LIMIT)
t = Minimum “on” time of LT1072 in current limit, ≈ 0.7µs
f = Operating frequency (40kHz)
Vf = Forward voltage of external catch diode at I(LIMIT)
I(LIMIT) = Current limit of LT1072 (2A)
RL = Internal series resistance of inductor
*Includes LT1072S8
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
BOTTOM VIEW
VC
VSW
1
4
2
3
VIN
CASE IS
GND
FB
K PACKAGE
4-LEAD TO-3 METAL CAN
TJMAX = 150°C, θJC = 8°C/W, θJA = 35°C/W
TJMAX = 100°C*, θJC = 8°C/W, θJA = 35°C/W
LT1072HVMK
LT1072MK
LT1072HVCK
LT1072CK
TOP VIEW
ORDER PART
NUMBER
TOP VIEW
GND
VC
1
8
2
7
FB
NC
3
6
4
5
E2
VSW
E1
VIN
N PACKAGE
8-LEAD PDIP
TJMAX = 100°C, θJA = 130°C/W
GND
VC
FB
NC
1
8
2
7
3
6
4
5
E2
VSW
E1
VIN
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 100°C, θJA = 130°C/W
LT1072CN8
LT1072CS8
S8 PART
MARKING
1072
J PACKAGE
8-LEAD CERAMIC DIP
TJMAX = 150°C, θJA = 100°C/W
LT1072MJ8
LT1072CJ8
OBSOLETE PACKAGE
OBSOLETE PACKAGE
Consider the S8 or N8 Packages for Alternate Source
ORDER PART
NUMBER
FRONT VIEW
5
VIN
4
VSW
GND
FB
VC
3
2
1
LT1072CT
LT1072HVCT
LT1072HVIT
T PACKAGE
5-LEAD TO-220
TJMAX = 100°C/W, θJC = 8°C/W, θJA = 50°C/W
TOP VIEW
NC
NC
GND
VC
FB
NC
NC
NC
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
NC
NC
E2
VSW
E1
VIN
NC
NC
ORDER PART
NUMBER
LT1072CSW
SW PACKAGE
16-LEAD PLASTIC SO WIDE
TJMAX = 100°C, θJC = 130°C/W
LT1072 • POI01
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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LT1072
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range. Unless otherwise specified, VIN = 15V, VC = 0.5V, VFB = VREF, output pin open.
SYMBOL
PARAMETER
CONDITlONS
VREF
Reference Voltage
Measured at Feedback Pin
VC = 0.8V
IB
Feedback Input Current
●
MIN
TYP
MAX
UNITS
1.224
1.214
1.244
1.244
1.264
1.274
V
V
350
750
1100
nA
nA
VFB = VREF
●
gm
AV
Error Amplifier
Transconductance
∆IC = ±25µA
Error Amplifier Source or
Sink Current
VC = 1.5V
Error Amplifier Clamp
Voltage
Hi Clamp, VFB = 1V
Lo Clamp, VFB = 1.5V
Reference Voltage Line
Regulation
3V ≤ VIN ≤ VMAX
VC = 0.8V
Error Amplifier Voltage Gain
0.9V ≤ VC ≤ 1.4V
6000
7000
µmho
µmho
150
120
200
●
350
400
µA
µA
2.3
0.52
V
V
0.03
%/V
%/V
1.8
0.25
500
3V ≤ VIN ≤ VMAX, VC = 0.6V
Control Pin Threshold
Duty Cycle = 0
●
Normal/Flyback Threshold on Feedback Pin
VFB
Flyback Reference Voltage
lFB = 50µA
●
Change in Flyback Reference Voltage
0.05 ≤ IFB ≤ 1mA
Flyback Reference Voltage
Line Regulation
lFB = 50µA
3V ≤ VIN ≤ VMAX (Note 4)
Flyback Amplifier Transconductance (gm)
∆IC = ±10µA
Flyback Amplifier Source
and Sink Current
VC = 0.6V Source
IFB = 50µA Sink
BV
Output Switch Breakdown
Voltage
3V ≤ VIN ≤ VMAX
ISW = 1.5mA
VSAT
Output Switch ON Resistance (Note 2)
ISW = 1.25A
3.0
9
0.8
0.6
0.9
1.08
1.25
V
V
0.4
0.45
0.54
V
15
14
16.3
17.6
18
V
V
Switch Current Limit
6.8
8.5
V
0.03
%/V
%/V
150
300
650
µmho
●
●
15
25
32
40
70
70
µA
µA
●
●
●
65
75
60
90
90
80
0.6
●
∆IIN
∆ISW
Supply Current Increase
During Switch ON Time
f
Switching Frequency
●
●
●
●
DC (max)
V
V
V
1
2
Duty Cycle = 50%
TJ ≥ 25°C
Duty Cycle = 50%
TJ < 25°C
Duty Cycle = 80% (Note 3)
Maximum Switch Duty Cycle
1.25
1.25
1
35
33
90
Flyback Sense Delay Time
3V ≤ VIN ≤ VMAX
VC = 0.05V
Shutdown Mode
Threshold Voltage
3V ≤ VIN ≤ VMAX
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Measured with VC in hi clamp, VFB = 0.8V.
●
100
50
Ω
A/V
3
3.5
2.5
A
A
A
25
35
mA/A
40
45
47
kHz
kHz
92
97
1.5
Shutdown Mode
Supply Current
V
mA
0.01
Control Voltage to Switch Current Transconductance
ILIM
V/V
6
4.5
LT1072
LT1072HV
LT1072S8
800
2.6
●
Supply Current
0.38
●
Minimum Input Voltage
IQ
3000
2400
4400
●
%
µs
100
250
µA
150
250
300
mV
mV
Note 3: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current is given by ILIM = 0.833 (2 – DC).
Note 4: VMAX = 55V for LT1072HV to avoid switch breakdown.
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LT1072
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch Current Limit vs Duty Cycle
Maximum Duty Cycle
4
Flyback Blanking Time
96
2.2
95
2.0
94
1.8
25°C
2
125°C
TIME (µs)
–55°C
DUTY CYCLE (%)
SWITCH CURRENT (A)
3
93
92
1.4
91
1.2
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)
1
0
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
LT1072 • TPC01
LT1072 • TPC02
Minimum Input Voltage
Isolated Mode Flyback Reference
Voltage
23
1.6
2.7
2.6
SWITCH CURRENT = 0A
2.5
2.4
2.3
–75 –50 –25
150°C
1.2
100°C
1.0
25°C
0.8
–55°C
0.6
0.4
0
0.25 0.5 0.75 1 1.25 1.5 1.75
SWITCH CURRENT (A)
LT1072 • TPC04
SWITCHING FREQUENCY
1.248
REFERENCE VOLTAGE (V)
25
TJ=
1
TJ = – 55°C
–1
–2
–4
–5
30
40
20
INPUT VOLTAGE (V)
50
60
LT1072 • TPC07
RFEEDBACK = 10kΩ
0 25 50 75 100 125 150
TEMPERATURE (C°)
Feedback Bias Current vs
Temperature
42
800
41
700
1.246
40
1.244
39
38
1.242
REFERENCE VOLTAGE
1.240
37
1.238
36
1.236
35
–3
10
17
LT1072 • TPC06
1.234
–75 –50 –25
34
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC08
FREQUENCY (kHz)
°C
2
0
18
15
–75 –50 –25
2
1.250
4
TJ = 150°C
RFEEDBACK = 1kΩ
19
Reference Voltage and Switching
Frequency vs Temperature
5
0
20
LT1072 • TPC05
Line Regulation
3
RFEEDBACK = 500Ω
21
16
0.2
0
0 25 50 75 100 125 150
TEMPERATURE (°C)
22
1.4
FLYBACK VOLTAGE (V)
SWITCH CURRENT = 1.25A
FEEDBACK BIAS CURRENT (nA)
2.8
SWITCH SATURATION VOLTAGE (V)
MINIMUM INPUT VOLTAGE (V)
LT1072 • TPC03
Switch Saturation Voltage
2.9
REFERENCE VOLTAGE CHANGE (mV)
1.6
600
500
400
300
200
100
0
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC09
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LT1072
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TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
(Shutdown Mode)
Supply Current vs Input Voltage*
15
70
14
60
50
40
30
20
160
TJ = 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
50% DUTY CYCLE
9
8
10% DUTY CYCLE
7
10
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
SWITCH CURRENT (A)
2
10
30
40
20
INPUT VOLTAGE (V)
40
50
60
Shutdown Mode Supply Current
490
–22
180
4500
480
–20
450
–14
440
–12
430
–10
FEEDBACK PIN CURRENT
(AT THRESHOLD)
410
400
–50 –25
0
–8
140
TJ = 150°C
120
100
80
60
– 55°C ≤ TJ ≤ 125°C
40
–6
20
–4
25 50 75 100 125 150
TEMPERATURE (°C)
0
0
–400
350
–350
–300
250
–250
200
–200
VOLTAGE
150
–150
100
–100
–50
0
0 25 50 75 100 125 150
TEMPERATURE (°C)
LT1072 • TPC16
10
VC PIN VOLTAGE (µA)
300
11
IDLE SUPPLY CURRENT (mA)
400
0
–75 –50 –25
3500
3000
2500
2000
1500
1000
0 25 50 75 100 125 150
TEMPERATURE (C°)
LT1072 • TPC15
Idle Supply Current vs
Temperature
VC VOLTAGE IS REDUCED UNTIL
REGULATOR CURRENT DROPS
BELOW 300µA
60
4000
LT1072 • TPC14
Shutdown Thresholds
50
50
Gm = ∆I (VC PIN)
∆V (FB PIN)
0
–75 –50 –25
10 20 30 40 50 60 70 80 90 100
VC PIN VOLTAGE (mV)
LT1072 • TPC13
CURRENT (OUT OF VC PIN)
20
40
30
SUPPLY VOLTAGE (V)
500
Feedback Pin Clamp Voltage
500
VC = 0.6V
450
9
FEEDBACK VOLTAGE (mV)
420
SUPPLY CURRENT (µA)
–18
–16
160
TRANSCONDUCTANCE (µmho)
5000
FEEDBACK PIN CURRENT (µA)
200
FEEDBACK PIN VOLTAGE
(AT THRESHOLD)
10
Error Amplifier Transconductance
–24
470
0
LT1072 • TPC12
500
460
VC = 0V
LT1072 • TPC11
Normal/Flyback Mode Threshold
on Feedback Pin
FEEDBACK PIN VOLTAGE (mV)
60
*UNDER VERY LOW OUTPUT CURRENT CONDITIONS,
DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH
10% OR LESS
LT1072 • TPC10
VC PIN VOLTAGE (mV)
VC = 50mV
80
0
0
*AVERAGE LT1072 POWER SUPPLY CURRENT IS
FOUND BY MULTIPLYING DRIVER CURRENT BY
DUTY CYCLE, THEN ADDING QUIESCENT CURRENT
100
0% DUTY CYCLE
5
0
120
20
6
0
TJ = 25°C
140
SUPPLY CURRENT (µA)
80
SUPPLY CURRENT (mA)
DRIVER CURRENT (mA)
Driver Current* vs Switch Current
8
7
6
5
VSUPPLY = 60V
VSUPPLY = 3V
4
400
300
150
100
50
0
LT1072 • TPC17
150°C
200
2
0 25 50 75 100 125 150
TEMPERATURE (°C)
25°C
250
3
1
–75 –50 –25
–55°C
350
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
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LT1072
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TYPICAL PERFOR A CE CHARACTERISTICS
Transconductance of Error
Amplifier
VC Pin Characteristics
0
200
5000
30
4000
60
Gm
3000
90
TJ = 25°C
0
–100
1000
150
0
180
–300
–1000
210
10M
–400
100k
1M
FREQUENCY (Hz)
900
800
120
10k
VFB = 1.5V (CURRENT INTO VC PIN)
100
2000
1k
Switch “Off” Characteristics
1000
SWITCH CURRENT (µA)
θ
300
PHASE (°)
TRANSCONDUCTANCE (µmho)
6000
–30
VC PIN CURRENT (µA)
7000
–200
VFB = 0.8V (CURRENT OUT OF VC PIN)
700
VSUPPLY = 55V
VSUPPLY = 40V
VSUPPLY = 15V
500
VSUPPLY = 3V
400
600
300
200
100
0
0.5
2.0
1.5
1.0
VC PIN VOLTAGE (V)
LT1072 • TPC19
0
2.5
0
10 20 30 40 50 60 70 80 90 100
SWITCH VOLTAGE (V)
LT1072 • TPC20
LT1072 • TPC21
W
BLOCK DIAGRA
VIN
16V
2.3V
REG
SWITCH
OUT
FLYBACK
ERROR
AMP
40kHz
OSC
LOGIC
DRIVER
ANTISAT
MODE
SELECT
COMP
–
FB
ERROR
AMP
VC
+
+
SHUTDOWN
CIRCUIT
CURRENT
AMP
1.24V
REF
0.15V
–
GAIN
≈6
0.16Ω
0.16Ω
E1*
E2
* ALWAYS CONNECT E1 TO GROUND PIN ON MINIDIP AND SURFACE MOUNT
PACKAGES. EMITTERS TIED TO GROUND ON TO-3 AND TO-220 PACKAGES
GND
LT1072 • BD01
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LT1072
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LT1072 OPERATIO
The LT1072 is a current mode switcher. This means that
switch duty cycle is directly controlled by switch current
rather than by output voltage. Referring to the block
diagram, the switch is turned “on” at the start of each
oscillator cycle. It is turned “off” when switch current
reaches a predetermined level. Control of output voltage is
obtained by using the output of a voltage sensing error
amplifier to set current trip level. This technique has
several advantages. First, it has immediate response to
input voltage variations, unlike ordinary switchers which
have notoriously poor line transient response. Second, it
reduces the 90 phase shift at midfrequencies in the energy
storage inductor. This greatly simplifies closed loop frequency compensation under widely varying input voltage
or output load conditions. Finally, it allows simple pulseby-pulse current limiting to provide maximum switch
protection under output overload or short conditions. A
low-dropout internal regulator provides a 2.3V supply for
all internal circuitry on the LT1072. This low-dropout
design allows input voltage to vary from 3V to 60V with
virtually no change in device performance. A 40kHz
oscillator is the basic clock for all internal timing. It turns
“on” the output switch via the logic and driver circuitry.
Special adaptive antisat circuitry detects onset of
saturation in the power switch and adjusts driver current
instantaneously to limit switch saturation. This minimizes
driver dissipation and provides very rapid turn-off of
the switch.
A 1.2V bandgap reference biases the positive input of the
error amplifier. The negative input is brought out for
output voltage sensing. This feedback pin has a second
function; when pulled low with an external resistor, it
programs the LT1072 to disconnect the main error
amplifier output and connects the output of the flyback
amplifier to the comparator input. The LT1072 will then
regulate the value of the flyback pulse with respect to the
supply voltage. This flyback pulse is directly proportional
to output voltage in the traditional transformer coupled
flyback topology regulator. By regulating the amplitude of
the flyback pulse, the output voltage can be regulated with
no direct connection between input and output. The output
is fully floating up to the breakdown voltage of the
transformer windings. Multiple floating outputs are easily
obtained with additional windings. A special delay network
inside the LT1072 ignores the leakage inductance spike at
the leading edge of the flyback pulse to improve output
regulation.
The error signal developed at the comparator input is
brought out externally. This pin (VC) has four different
functions. It is used for frequency compensation, current
limit adjustment, soft starting, and total regulator
shutdown. During normal regulator operation this pin sits
at a voltage between 0.9V (low output current) and 2.0V
(high output current). The error amplifiers are current
output (gm) types, so this voltage can be externally
clamped for adjusting current limit. Likewise, a capacitor
coupled external clamp will provide soft start. Switch duty
cycle goes to zero if the VC pin is pulled to ground through
a diode, placing the LT1072 in an idle mode. Pulling the VC
pin below 0.15V causes total regulator shutdown, with
only 50µA supply current for shutdown circuitry biasing.
See AN-19 for full application details.
Extra Pins on the MiniDIP and Surface Mount Packages
The 8 and 16-pin versions of the LT1072 have the emitters
of the power transistor brought out separately from the
ground pin. This eliminates errors due to ground pin
voltage drops and allows the user to reduce switch current
limit 2:1 by leaving the second emitter (E2) disconnected.
The first emitter (E1) should always be connected to the
ground pin. Note that switch “on” resistance doubles
when E2 is left open, so efficiency will suffer somewhat
when switch currents exceed 100mA. Also, note that chip
dissipation will actually increase with E2 open during
normal load operation, even though dissipation in current
limit mode will decrease. See “Thermal Considerations.”
Thermal Considerations When Using Small Packages
The low supply current and high switch efficiency of the
LT1072 allow it to be used without a heat sink in most
applications when the TO-220 or TO-3 package is selected.
These packages are rated at 50°C/W and 35°C/W
respectively. The small packages, however, are rated at
greater than 100°C/W. Care should be taken with these
packages to ensure that the worse case input voltage and
load current conditions do not cause excessive die
temperatures. The following formulas can be used as a
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LT1072
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LT1072 OPERATIO
rough guide to calculate LT1072 power dissipation. For
more details, the reader is referred to Application Note 19
(AN19), “Efficiency Calculations” section.
Average supply current (including driver current) is:
IIN ≈ 6mA + ISW(0.004 + DC/40)
ISW = switch current
DC = switch duty cycle
Switch power dissipation is given by:
PSW = (ISW)2 • RSW • DC
RSW = LT1072 switch “on” resistance (1Ω maximum)
Total power dissipation is the sum of supply current times
input voltage plus switch power:
PTOT = (llN)(VIN) + PSW
In a typical example, using a boost converter to generate
12V @ 0.12A from a 5V input, duty cycle is approximately
60%, and switch current is about 0.65A, yielding:
llN = 6mA + 0.65(0.004 + DC/40) = 18mA
PSW = (0.65)2 • 1Ω • (0.6) = 0.25W
PTOT = (5V)(0.018A) + 0.25 = 0.34W
Temperature rise in a plastic miniDIP would be 130°C/W
times 0.34W, or approximately 44°C. The maximum
ambient temperature would be limited to 100°C
(commercial temperature limit) minus 44°C, or 56°C.
In most applications, full load current is used to calculate
die temperature. However, if overload conditions must
also be accounted for, four approaches are possible. First,
if loss of regulated output is acceptable under overload
conditions, the internal thermal limit of the LT1072 will
protect the die in most applications by shutting off switch
current. Thermal limit is not a tested parameter, however,
and should be considered only for non-critical applications
with temporary overloads. A second approach is to use the
larger TO-220 (T) or TO-3 (K) package which, even without
a heat sink, may limit die temperatures to safe levels under
overload conditions. In critical situations, heat sinking
of these packages is required; especially if overload
conditions must be tolerated for extended periods of time.
The third approach for lower current applications is to
leave the second switch emitter open. This increases
switch “on” resistance by 2:1, but reduces switch current
limit by 2:1 also, resulting in a net 2:1 reduction in I2R
switch dissipation under current limit conditions.
The fourth approach is to clamp the VC pin to a voltage less
than its internal clamp level of 2V. The LT1072 switch
current limit is zero at approximately 1V on the VC pin and
2A at 2V on the VC pin. Peak switch current can be
externally clamped between these two levels with a diode.
See AN-19 for details.
LT1072 Synchronizing
The LT1072 can be externally synchronized in the frequency
range of 48kHz to 70kHz. This is accomplished as shown
in the accompanying figures. Synchronizing occurs when
the VC pin is pulled to ground with an external transistor.
To avoid disturbing the DC characteristics of the internal
error amplifier, the width of the synchronizing pulse
should be under 1µs. C2 sets the pulse width at ≈ 0.35µs.
The effect of a synchronizing pulse on the LT1072
amplifier offset can be calculated from:
KT (t )(f ) I + VC
q S S C R3
∆VOS =
IC
( (
(
(
KT
= 26mV at 25°C
q
tS = pulse width
fS = pulse frequency
IC = LT1072 VC source current (≈ 200µA)
VC = LT1072 operating VC voltage (1V to 2V)
R3 = resistor used to set mid-frequency “zero” in LT1072
frequency compensation network.
With tS = 0.35µs, fS = 50kHz, VC = 1.5V, and R3 = 2KΩ,
offset voltage shift is ≈2.2mV. This is not particularly
bothersome, but note that high offsets could result
if R3 were reduced to a much lower value. Also, the
synchronizing transistor must sink higher currents with
low values of R3, so larger drives may have to be used. The
transistor must be capable of pulling the VC pin to within
200mV of ground to ensure synchronizing.
1072fc
8
LT1072
U
LT1072 OPERATIO
Synchronizing with Bipolar Transistor
Synchronizing with MOS Transistor
VIN
VIN
LT1072
LT1072
VC
GND
C2
68pF
R3
VC
GND
R1
3k
R3
2N2369
C1
R2
2.2k
VN2222*
C1
FROM 5V
LOGIC
C2
200pF
D1
1N4158
R2
2.2k
D2
1N4158
FROM 5V
LOGIC
*SILICONIX OR EQUIVALENT
LT1072 • OP01
LT1072 • OP02
U
TYPICAL APPLICATIO S
Totally Isolated Converter
OPTIONAL
OUTPUT FILTER
1:N
R4
2.7k
C3
0.47µF
D1
+
N
N
VIN
VIN
5V
C5
25µF*
15V
+
L1
10µH
+
C1
200µF
COM
C4
200µF
L2
–15V 10µH
+
C5
200µF
C6
200µF
VSW
+
LT1072
VC
GND
N = 0.875 = 7:8
FOR VOUT = 15V
FB
500Ω
C2
0.01µF
R2
5k
*REQUIRED IF INPUT LEADS ≥ 2”
≈ 16V
VIN
0
tOFF
SWITCH VOLTAGE
tON
VOUT + Vf (Vf = DIODE FORWARD VOLTAGE)
SECONDARY VOLTAGE
0V
N • VIN
LT1072 • TA03
1072fc
9
LT1072
U
TYPICAL APPLICATIO S
Flyback Converter
L2
10µH
C4
200µF
OPTIONAL
FILTER
D1
VIN
20 TO 30V
R4
1k
**
+
N* = 1
3
b
0V
VOUT + Vf
c
C4 +
25µF*
N • VIN SECONDARY VOLTAGE
AREA “c” = AREA “d” TO MAINTAIN
ZERO DC VOLTS ACROSS SECONDARY
0V
d
C1
500µF
∆I
IPRI
D2
VIN
R1
3.74k
VSW
PRIMARY CURRENT
0
LT1072
IPRI
SECONDARY CURRENT
N
0
IPRI
VC FB
GND
+ Vf
V
PRIMARY FLYBACK VOLTAGE = OUT
N
LT1072 SWITCH VOLTAGE
AREA “a” = AREA “b” TO MAINTAIN
ZERO DC VOLTS ACROSS PRIMARY
a
VIN
VOUT
5V
1.5A
1 N*
C3
0.47µF
CLAMP TURN-ON
SPIKE
VSNUB
LT1070 SWITCH CURRENT
C2
0.15µF
R2
1.24k
R3
1.5k
0
IPRI
SNUBBER DIODE CURRENT
0
*REQUIRED IF INPUT LEADS ≥ 2"
**OPTIONAL TO REPLACE R4 AND C3
(I ) (LL)
t = PRI
VSNUB
Negative to Positive Buck-Boost Converter
LT1072 • TA04
External Current Limit
L2
L1**
220µH
OPTIONAL
OUTPUT
FILTER
C4
25µF*
OPTIONAL
INPUT
FILTER
+
C2
1000µF
LT1072
VOUT
12V, 0.5A
+
R1
11.3k
+
–
GND
C1
0.22µF
R3
2.2k
GND
VIN
Q1
R1
1k
VC FB
L3
VIN
–12V
VSW
VSW
LT1072
D1
VIN
VIN
C3
VC
FB
R2
Q1
R2
1.24k
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING 52626
C1
1000pF
RS
C2
NOTE THAT THE LT1072 GND PIN
IS NO LONGER COMMON TO VIN (–)
LT1072 • TA06
LT1072 • TA05
1072fc
10
LT1072
U
TYPICAL APPLICATIO S
Positive to Negative Buck-Boost Converter
D3†
1N4001
R5†
470Ω, 1W
C5
100µF*
VIN
C4
5µF
+
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING 92113
VIN
10 TO 30V
†
VSW
LT1072
D2
1N914
R1
10.7k
FB
VC
GND
R4
47Ω
TO AVOID START-UP PROBLEMS
FOR INPUT VOLTAGES BELOW 10V,
CONNECT ANODE OF D3 TO VIN,
AND REMOVE R5. C1 MAY BE
REDUCED FOR LOWER OUTPUT
CURRENTS. C1 ≈ (500µF)(IOUT).
FOR 5V OUTPUTS, REDUCE R3
TO 1.5k, INCREASE C2 TO 0.3µF,
AND REDUCE R6 TO 100Ω
R3
5k
R2
1.24k
C2
0.1µF
+
+
C3
2µF
C1†
C
1000µF
R6
470Ω
D1
VOUT
–12V AT 2A
L1**
200µH
LT1072 • TA07
External Current Limit
VX
LT1072
R2
≈ 2V
D1
R1
500Ω
GND
VC
LT1072 • TA08
Voltage Boosted Boost Converter
R4
1.5k
1/2W
C3
0.68
D2
VIN
VIN
15V
TOTAL INDUCTANCE = 8mH
1
INTERLEAVE PRIMARY AND
L1
N = 5 SECONDARY FOR LOW LEAKAGE
INDUCTANCE
VSW
+
LT1072
D1
R1
98k
GND
R3
10k
C2
0.047µF
VOUT
100V AT 75mA
VC FB
R2
1.24k
+
C1
200µF
LT1072 • TA09
1072fc
11
LT1072
U
TYPICAL APPLICATIO S
Driving High Voltage FET
(for Offline Applications, See AN-25)
G
D
Q1
D1
VIN
VSW
+
10 TO 20V
LT1072
GND
LT1072 • TA10
Negative Buck Converter
C2
500µF
D1
VIN
C3
25µF*
+
VSW
GND
R1
4.64k
LOAD
–5.2V AT 1A
L1**
220µH
Q1
2N3906
LT1072
OPTIONAL
INPUT
FILTER
+
VC FB
C1
L3
R3
OPTIONAL +
OUTPUT
FILTER
R2
1.24k
VIN
–20V
C4
200µF
L2
4µH
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING 52626
LT1072 • TA11
Positive Buck Converter
VIN
D3
L2
VIN
C3
2.2µF
C5*
25µF
4µH
VSW
OPTIONAL
OUTPUT
FILTER
+
LT1072
R1
3.74k
+
C5
200µF
D2
VC FB
GND
R2
1.24k
R3
470Ω
C1
1µF
C2
1µF
r
D1
+
1N914
R4
10Ω
L1**
220µH
C4
500µF
+
5V, 1A
100mA
MINIMUM
*REQUIRED IF INPUT LEADS ≥ 2"
**PULSE ENGINEERING 52626
LT1072 • TA12
1072fc
12
LT1072
U
TYPICAL APPLICATIO S
Negative Boost Regulator
D2
VIN
VSW
R1
27k
LT1072
C4
470µF*
+
+
+
R0
(MINIMUM
LOAD)
C1
1000µF
VC FB
GND
R3
3.3k
C2
0.22µF
L1
200µH
VIN
–15V
C3
10µF
R2
1.24k
D1
VOUT
–28V AT 0.25A
*REQUIRED IF INPUT LEADS ≥ 2"
LT1072 • TA13
U
PACKAGE DESCRIPTIO
J8 Package
8-Lead CERDIP (Narrow .300 Inch, Hermetic)
(Reference LTC DWG # 05-08-1110)
CORNER LEADS OPTION
(4 PLCS)
.023 – .045
(0.584 – 1.143)
HALF LEAD
OPTION
.045 – .068
(1.143 – 1.650)
FULL LEAD
OPTION
.005
(0.127)
MIN
.405
(10.287)
MAX
8
7
6
5
.025
(0.635)
RAD TYP
.220 – .310
(5.588 – 7.874)
1
2
.300 BSC
(7.62 BSC)
3
4
.200
(5.080)
MAX
.015 – .060
(0.381 – 1.524)
.008 – .018
(0.203 – 0.457)
0° – 15°
NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE
OR TIN PLATE LEADS
.045 – .065
(1.143 – 1.651)
.014 – .026
(0.360 – 0.660)
.100
(2.54)
BSC
.125
3.175
MIN
J8 0801
OBSOLETE PACKAGE
1072fc
13
LT1072
U
PACKAGE DESCRIPTIO
K Package
4-Lead TO-3 Metal Can
(Reference LTC DWG # 05-08-1311)
0.320 – 0.350
(8.13 – 8.89)
0.760 – 0.775
(19.30 – 19.69)
0.060 – 0.135
(1.524 – 3.429)
0.420 – 0.480
(10.67 – 12.19)
0.038 – 0.043
(0.965 – 1.09)
1.177 – 1.197
(29.90 – 30.40)
0.655 – 0.675
(16.64 – 19.05)
0.470 TP
P.C.D.
0.151 – 0.161
(3.84 – 4.09)
DIA 2 PLC
0.167 – 0.177
(4.24 – 4.49)
R
0.490 – 0.510
(12.45 – 12.95)
R
72°
18°
K4(TO-3) 1098
OBSOLETE PACKAGE
N8 Package
8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
.400*
(10.160)
MAX
8
7
6
5
1
2
3
4
.255 ± .015*
(6.477 ± 0.381)
.300 – .325
(7.620 – 8.255)
.008 – .015
(0.203 – 0.381)
+.035
.325 –.015
(
8.255
+0.889
–0.381
)
.045 – .065
(1.143 – 1.651)
.130 ± .005
(3.302 ± 0.127)
.065
(1.651)
TYP
.100
(2.54)
BSC
.120
(3.048) .020
MIN
(0.508)
MIN
.018 ± .003
(0.457 ± 0.076)
N8 1002
NOTE:
1. DIMENSIONS ARE
INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
1072fc
14
LT1072
U
PACKAGE DESCRIPTIO
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.050 BSC
7
8
5
6
N
N
.245
MIN
.160 ±.005
1
.030 ±.005
TYP
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
2
3
N/2
N/2
RECOMMENDED SOLDER PAD LAYOUT
1
.010 – .020
× 45°
(0.254 – 0.508)
3
2
4
.053 – .069
(1.346 – 1.752)
.008 – .010
(0.203 – 0.254)
.004 – .010
(0.101 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
1. DIMENSIONS IN
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0502
SW Package
16-Lead Plastic Small Outline (Wide .300 Inch)
(Reference LTC DWG # 05-08-1620)
.050 BSC .045 ±.005
.030 ±.005
TYP
.398 – .413
(10.109 – 10.490)
NOTE 4
16
N
15
14
13
12
11
10
9
N
.325 ±.005
.420
MIN
.394 – .419
(10.007 – 10.643)
NOTE 3
1
2
3
N/2
N/2
RECOMMENDED SOLDER PAD LAYOUT
1
.291 – .299
(7.391 – 7.595)
NOTE 4
.010 – .029 × 45°
(0.254 – 0.737)
.005
(0.127)
RAD MIN
2
3
4
5
6
.093 – .104
(2.362 – 2.642)
7
8
.037 – .045
(0.940 – 1.143)
0° – 8° TYP
.009 – .013
(0.229 – 0.330)
NOTE 3
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
.050
(1.270)
BSC
.004 – .012
(0.102 – 0.305)
.014 – .019
(0.356 – 0.482)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS
4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
S16 (WIDE) 0502
1072fc
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 its circuits as described herein will not infringe on existing patent rights.
15
LT1072
U
PACKAGE DESCRIPTIO
T Package
5-Lead Plastic TO-220 (Standard)
(Reference LTC DWG # 05-08-1421)
.165 – .180
(4.191 – 4.572)
.147 – .155
(3.734 – 3.937)
DIA
.390 – .415
(9.906 – 10.541)
.045 – .055
(1.143 – 1.397)
.230 – .270
(5.842 – 6.858)
.460 – .500
(11.684 – 12.700)
.570 – .620
(14.478 – 15.748)
.620
(15.75)
TYP
.330 – .370
(8.382 – 9.398)
.700 – .728
(17.78 – 18.491)
SEATING PLANE
.152 – .202
.260 – .320 (3.861 – 5.131)
(6.60 – 8.13)
.095 – .115
(2.413 – 2.921)
.155 – .195*
(3.937 – 4.953)
.013 – .023
(0.330 – 0.584)
BSC
.067
(1.70)
.028 – .038
(0.711 – 0.965)
.135 – .165
(3.429 – 4.191)
* MEASURED AT THE SEATING PLANE
T5 (TO-220) 0801
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1070/HV
5A ISW, 40kHz, High Efficiency Switching Regulator
VIN=3V to 40/60V, VOUT up to 65/75V, IQ=6mA, ISD
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