LT1082M [Linear]
1A High Voltage, Efficiency Switching Voltage Regulator; 1A高电压，效率开关稳压器
| 型号： | LT1082M |
| 厂家： | 
Linear |
| 描述： | 1A High Voltage, Efficiency Switching Voltage Regulator |
| 文件： | 总12页 (文件大小：251K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1082
1A High Voltage, Efficiency
Switching Voltage Regulator
U
DESCRIPTIO
EATURE
S
F
■
■
■
■
■
■
Wide Input Voltage Range: 3V to 75V
High Switch Voltage: 100V
The LT1082 is a monolithic high voltage switching
regulator. It can be operated in all standard switching
configurations including buck, boost, flyback, forward,
and inverting. A 1A high efficiency switch is included on
the die along with all oscillator, control, and protection
circuitry.
Low Quiescent Current: 4.5mA
Internal 1A Switch
Shutdown Mode Draws Only 120µA Supply Current
Isolated Flyback Regulation Mode for Fully Floating
Outputs
Can Be Externally Synchronized
Available in MiniDIP and TO-220 Packages
Same Pinout as LT1072
TheLT1082operateswithsupplyvoltagesfrom3Vto75V,
switch voltage up to 100V and draws only 4.5mA quies-
cent current. It can deliver load power up to 20W with no
external power devices. By utilizing current-mode switch-
ing techniques, it provides excellent AC and DC load and
line regulation.
■
■
■
O U
PPLICATI
A
S
■
■
■
Telecom 5V Supply at 0.7A from –48V
90V Supply at 120mA from 15V
An externally activated shutdown mode reduces total
supply current to 120µA typical for standby operation.
Totallyisolatedandregulatedoutputscanbegeneratedby
using the optional “isolated flyback regulation mode” built
into the LT1082, without the need for optocouplers or
extra transformer windings.
All Applications Using LT1072 (See Below for
Specification Differences)
LT1082 and LT1072 Major Specification Differences
LT1082C
3V to 75V
100V
LT1072HV
3V to 60V
75V
1.25A
6mA
V
V
IN
The LT1082 has a unique feature to provide high voltage
short-circuitprotection. WhentheFBpinispulleddownto
0.6V and the current out of the pin reaches approximately
350µA, the switching frequency will shift down from
SW
Switch Current Limit
Quiescent Current
Operating Frequency
1A
4.5mA
60kHz
40kHz
16 + 0.35 (7kΩ/R )
Flyback Reference Voltage 16.2 + 0.6 (35kΩ/R
)
FB
FB
60kHz to 12kHz.
USER NOTE: This data sheet is only intended to provide specifications, graphs, and a general
functional description of the LT1082. Application circuits are included to show the capability of the
LT1082. Acompletedesignmanual(AN19)andSwitcherCAD(LTCSwitchingPowerSupplyDesign
Program) 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 LT1082 by factoring in the lower switch current rating.
TheLT1082isnearlyidenticaltothelowervoltageLT1072.
Forthemajordifferencesinspecifications,seethetableon
the left.
Telecom 5V Supply Maximum Output
Current vs Input Voltage
Negative-to-Positive Telecom 5V Supply
*D1
**250µH
V
1.0
OUT
5V, 0.7A
NOTE: MAXIMUM OUTPUT
f = 45kHz
CURRENT IS A FUNCTION
+
470µF
3.83k
I
LIMIT = 1.07A
SW
OF INPUT VOLTAGE. SEE
THE GRAPH ON THE RIGHT.
0.9
0.8
0.7
0.6
0.5
0.4
L=550µH
L=450µH
L=350µH
10V
CHEMI-CON
SXE SERIES
V
V
IN
SW
Q1
2N5401
33µF
80V
L=250µH
+
LT1082
CHEMI-CON
SXE SERIES
FB
GND
V
C
MOTOROLA MUR110 (100V, 1A)
*
69 TURNS OF #28 AWG WIRE ON A
MICROMETALS T60 TYPE 52 CORE.
**
L=150µH
1.1k
NOTE: THIS CORE IS LOW COST, BUT
HAS HIGHER CORE LOSS AND IS LARGER
THAN NECESSARY FOR LOWER CURRENT
APPLICATIONS. FOR SMALLER INDUCTORS
OR HIGHER EFFICIENCY, USE A LOW LOSS
CORE SUCH AS MAGNETICS INC. KOOL Mµ
OR MOLYPERMALLOY.
4.7k
0.22µF
0.01µF
L=100µH
–20V
TO –70V
0
–10 –20 –30 –40 –50 –60 –70 –80 –90
INPUT VOLTAGE (V)
1082 TA01
1082 TA02
1
LT1082
W W W
U
ABSOLUTE AXI U RATI GS
Supply Voltage ....................................................... 75V
Switch Output Voltage .......................................... 100V
Feedback Pin Voltage (Transient, 1ms) ................ ±15V
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Operating Junction Temperature Range
LT1082M ......................................... – 55°C to 150°C
LT1082I ........................................... – 40°C to 125°C
LT1082C............................................... 0°C to 100°C
W
U
/O
PACKAGE RDER I FOR ATIO
TOP VIEW
FRONT VIEW
FRONT VIEW
5
4
3
2
1
V
V
GND
FB
5
4
3
2
1
IN
SW
V
V
GND
FB
GND
1
2
3
4
E2
V
8
7
6
5
IN
SW
V
C
SW
FB
E1
V
V
C
V
C
NC
IN
Q PACKAGE
5-LEAD DD
T PACKAGE
5-LEAD TO-220
J8 PACKAGE
8-LEAD CERAMIC DIP 8-LEAD PLASTIC DIP
N8 PACKAGE
T
JMAX = 100°C, θJA = 40°C/W (CQ)
TJMAX = 125°C, θJA = 40°C/ W (IQ)
TJMAX = 150°C, θJA = 100°C/W (MJ8)
TJMAX = 100°C, θJA = 90°C/W (CN8)
T
JMAX = 100°C, θJA = 75°C/W, θJC = 8°C/W (CT)
TJMAX = 125°C, θJA = 75°C/W, θJC = 8°C/W (IT)
NOTE: θJA VARIES FROM 25°C/W TO 50°C/W
DEPENDING ON BOARD COMPOSITION.
TJMAX = 125°C, θJA = 90°C/W (IN8)
ORDER PART NUMBER
ORDER PART NUMBER
ORDER PART NUMBER
LT1082CQ
LT1082IQ
LT1082CT
LT1082IT
LT1082MJ8
LT1082CN8
LT1082IN8
ELECTRICAL CHARACTERISTICS
VIN = 15V, VC = 0.5V, VFB = VREF, output pin open, unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Reference Voltage
Measured at Feedback Pin
V = 0.8V
C
1.224 1.244
1.214 1.244
1.264
1.274
V
V
REF
●
●
●
●
I
Feedback Input Current
V
FB
= V
REF
350
750
1100
nA
nA
B
g
m
Error Amplifier
Transconductance
∆I = ±25µA
C
3000 4400
2400
6000
7000
µmho
µmho
Error Amplifier Source or
Sink Current
V = 1.5V
C
150
120
200
400
400
µA
µA
Error Amplifier Clamp
Voltage
Hi Clamp, V = 1V
1.8
0.12 0.22
2.3
0.36
V
V
FB
Lo Clamp, V = 1.5V
FB
Reference Voltage Line Regulation
Error Amplifier Voltage Gain
Minimum Input Voltage
3V ≤ V ≤ V
, V = 0.8V
●
●
0.03
%/V
V/V
V
IN
MAX
C
A
V
0.9V ≤ V ≤ 1.4V
350
650
2.6
C
3.0
2
LT1082
ELECTRICAL CHARACTERISTICSVIN = 15V, VC = 0.5V, VFB = VREF, output pin open, unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Supply Current
3V ≤ V ≤ V
, V = 0.6V
C
4.5
0.9
7.0
mA
Q
IN
MAX
Control Pin Threshold
Duty Cycle = 0
0.7
0.5
1.1
1.25
V
V
●
Normal/Flyback Threshold
on Feedback Pin
0.58
0.67
60
0.8
V
f
Switching Frequency
50
45
70
75
kHz
kHz
●
●
800µA ≥ I ≥ 450µA
12
115
1.5
kHz
V
FB
BV
Output Switch Breakdown Voltage
3V ≤ V ≤ V
, I = 1.5mA
MAX SW
100
IN
Control Voltage to Switch
Current Transconductance
A/V
V
Flyback Reference Voltage
I
= 60µA
FB
17
16
18.6
20.5
21.5
V
V
FB
●
Change in Flyback Reference Voltage
60µA ≤ I ≤ 200µA
3.5
4.6
0.01
300
6.5
0.03
500
V
%/V
FB
Flyback Reference Voltage Line Regulation
I
= 60µA, 3V ≤ V ≤ V
FB IN MAX
Flyback Amplifier Transconductance (g )
∆I = ±10µA
C
150
µmho
m
Flyback Amplifier Source
and Sink Current
V = 0.6V Source
●
●
15
30
32
50
70
90
µA
µA
C
I
= 60µA Sink
FB
V
Output Switch “On” Resistance (Note 1)
I
= 0.7A (LT1082C), I = 0.5A (LT1082M)
●
0.8
1.2
Ω
SAT
LIM
SW
SW
I
Switch Current Limit
(LT1082C)
Duty Cycle = 20%
Duty Cycle ≤ 50%
Duty Cycle = 80% (Note 2)
●
●
●
1.07
1.0
0.8
2.6
2.6
2.4
A
A
A
Switch Current Limit
(LT1082I)
Duty Cycle = 20%
Duty Cycle ≤ 50%
Duty Cycle = 80% (Note 2)
●
●
●
0.85
0.8
0.65
2.8
2.8
2.6
A
A
A
Switch Current Limit
(LT1082M)
Duty Cycle = 20%
Duty Cycle ≤ 50%
Duty Cycle = 80% (Note 2)
●
●
●
0.75
0.7
0.6
3.0
3.0
2.8
A
A
A
∆I
Supply Current Increase
During Switch-On Time
35
45
mA/A
IN
∆I
SW
DC
Maximum Switch Duty Cycle
Flyback Sense Delay Time
85
92
1.5
120
150
97
%
µs
MAX
Shutdown Mode Supply Current
3V ≤ V ≤ V , V = 0.05V
350
µA
IN
MAX
C
Shutdown Mode
Threshold Voltage
3V ≤ V ≤ V
70
50
250
300
mV
mV
IN
MAX
●
The
temperature range.
Note 1: Measured with V in hi clamp, V = 0.8V.
●
denotes the specifications which apply over the operating
Note 2: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current decreases linearly.
C
FB
3
LT1082
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Suggested Core Size and
Inductance for Telecom
Telecom 5V Supply Short-Circuit
Frequency Shift-Down
Telecom 5V Supply Efficiency
5V Supply
80
70
60
50
40
30
20
10
0
79
76
73
70
67
64
61
58
55
TYPE 52
POWDERED OR MOLY-
IRON PERMALLOY
KOOL Mµ
T
= 25°C
A
LOAD
V
V
= –20V
= –40V
= –60V
IN
CURRENT
100mA
200mA
400mA
600mA
800mA
T38 250µH T38 200µH
T50 250µH T38 150µH
T60 250µH T50 150µH
T60 250µH T50 200µH
T80 350µH T80 350µH
IN
V
IN
1082 GA
V
= –70V
1
IN
L = 250µH
R = 0.08Ω
2
0
3
4
6
5
4
3
2
1
0
OUTPUT VOLTAGE (V)
POWER OUTPUT (W)
NOTE: THIS GRAPH IS BASED ON LOW CORE LOSS
PERMALLOY INDUCTOR. IF POWDERED IRON CORE
INDUCTOR IS USED, THE CORE LOSS IS TYPICALLY
1082 G02
100mW HIGHER.
1082 G01
Short-Circuit Frequency
Shift-Down vs Feedback Current
Maximum Duty Cycle
Switch Current Limit
4
97
70
60
50
40
30
20
10
0
T
= –55°C
A
T
T
= 0°C
A
A
96
95
94
93
92
91
90
3
2
= 150°C
T
= 25°C
T
= –55°C
= 150°C
J
J
T
J
1
0
0
10 20 30 40 50 60 70 80 90 100
–75
0
50 75 100 125 150 175
100 200
400 500 600 700 800
–50 –25
25
0
300
TEMPERATURE (°C)
DUTY CYCLE (%)
FEEDBACK CURRENT (µA)
1082 G04
1082 G05
1082 G03
Flyback Blanking Time
Switch Saturation Voltage
Minimum Input Voltage
2.9
2.2
2.0
1.8
1.6
1.4
1.2
1.0
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.8
2.7
2.6
2.5
2.4
2.3
T = 150°C
J
I
= 1A
= 0A
SW
T = 100°C
J
T = 25°C
J
I
SW
T = –50°C
J
–75
0
50 75 100 125 150
–75
0
50 75 100 125 150
–50 –25
25
–50 –25
25
0.50
1.00 1.25
1.75
1.50
2.00
0
0.25
0.75
TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
SWITCH CURRENT (A)
1082 G07
1082 G06
1082 G08
4
LT1082
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Reference Voltage and Switching
Frequency vs Temperature
Isolated Mode Flyback
Reference Voltage
Line Regulation
70
65
60
55
50
45
1.250
1.245
1.240
1.235
1.230
1.225
25
24
23
22
21
20
19
18
17
16
15
5
4
R
FB
= 3k
V
REF
3
FREQ
2
1
R
FB
= 6k
T
= –55°C
J
0
R
FB
= 10k
–1
–2
–3
–4
–5
T
= 150°C
= 25°C
J
T
J
–75
0
50 75 100 125 150
175
–50 –25
25
–75
0
50 75 100 125 150
175
–50 –25
25
0
60 70
10 20 30
40
INPUT VOLTAGE (V)
50
80
TEMPERATURE (°C)
TEMPERATURE (°C)
1082 G11
1082 G09
1082 G10
Feedback Bias Current vs
Temperature
Normal/Feedback Mode
Shutdown Mode Supply Current
Threshold on Feedback Pin
800
700
600
500
400
300
200
100
0
750
725
700
675
650
625
600
575
550
525
500
–24
–22
–20
–18
–16
–14
–12
–10
–8
200
180
160
140
120
100
80
FEEDBACK PIN VOLTAGE
(AT THRESHOLD)
–55°C ≤ T ≤ 125°C
J
T = 150°C
J
FEEDBACK PIN CURRENT
(AT THRESHOLD)
60
40
–6
20
–4
0
–75
0
50 75 100 125 150
175
–50 –25
25
–75
0
50 75 100 125 150
–50 –25
25
175
0
30
50 60 70 80 90
10 20
40
100
TEMPERATURE (°C)
TEMPERATURE (°C)
V
PIN VOLTAGE (mV)
C
1082 G12
1082 G16
1082 G17
Supply Current vs Supply Voltage
(Shutdown Mode)
Driver Current* vs Switch Current
Supply Current vs Input Voltage**
14
13
12
11
10
9
200
160
120
80
100
90
80
70
60
50
40
30
20
10
0
V
= 50mV
C
90% DUTY CYCLE
8
50% DUTY CYCLE
10% DUTY CYCLE
V
= 0V
C
7
6
5
40
0% DUTY CYCLE
4
3
0
2
60
40
SUPPLY VOLTAGE (V)
0
20
40 50
30
INPUT VOLTAGE (V)
70 80
0
10 20 30
50 60 70 80
10
0
0.6
1.0 1.2 1.4 1.6 1.8
2.0
0.2 0.4
0.8
SWITCH CURRENT (A)
* AVERAGE SUPPLY CURRENT
=+IDC(2.9 + 10–2 + 10–5
1082 G15
**UNDER VERY LOW OUTPUT CURRENT CONDITIONS,
DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH
2
I
I
)
SW
Q
SW
I
I
= QUIESCENT CURRENT, DC = DUTY CYCLE,
= SWITCH CURRENT
1082 G14
10% OR LESS.
Q
1082 G13
SW
5
LT1082
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Idle Supply Current vs
Temperature
Shutdown Thresholds
Error Amplifier Transconductance
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
400
350
300
250
200
150
100
50
–400
–350
–300
–250
–200
–150
–100
–50
10
9
(V PIN)
C
V = 0.6V
C
∆I
∆V
g
m
=
(FB PIN)
CURRENT
(OUT OF V PIN)
8
C
7
6
V
= 75V
= 3V
IN
VOLTAGE AT V PIN
5
C
V
IN
4
3
2
0
–75
0
175
0
–75
1
0
50 75 100 125 150
–75
0
50 75 100 125 150
175
–50 –25
25
–50 –25
25
0
50 75 100 125 150
–50 –25
25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1082 G19
1082 G20
1082 G18
Feedback Pin Clamp Voltage
Switch “Off” Characteristics
800
700
600
500
400
300
200
500
450
400
350
300
250
200
150
100
50
A. V = 3V
IN
B. V = 15V
IN
C. V = 40V
IN
T
J
= –55°C
D. V = 55V
IN
E. V = 75V
IN
T
= 25°C
J
T
= 150°C
J
A
B
C
D
E
0
0
0.1 0.2
0.5
0.7 0.8 0.9
1.1
1.0
0.3 0.4
0.6
0
30
50 60 70 80 90
100
10 20
40
FEEDBACK CURRENT (mA)
SWITCH VOLTAGE (V)
1082 G21
1082 G22
Transconductance of Error
Amplifier
VC Pin Characteristics
7000
6000
5000
4000
3000
2000
1000
0
–30
400
300
T = 25°C
J
0
θ
30
V
= 1.5V
200
FB
(CURRENT INTO V PIN)
C
g
m
60
100
90
0
120
150
180
210
–100
–200
–300
–400
V
FB
= 0.8V
(CURRENT OUT OF V PIN)
C
–1000
1k
10k
100k
1M
10M
0
1.5
VPIN VOLTAGE (V)
2.0
0.5
1.0
2.5
FREQUENCY (Hz)
C
1082 G24
1082 G23
6
LT1082
W
BLOCK DIAGRA
V
SWITCH OUT
16.2V
IN
2.3V
REG
FLYBACK
ERROR
AMP
OSC
60kHz
14kHz
DRIVER
LOGIC
COMP
ANTI-SAT
MODE SELECT
–
FB
+
–
CURRENT
AMP
ERROR
+
0.2Ω
V
C
0.2Ω
AMP
GAIN ≈ 5
E1*
E2
SHUTDOWN
CIRCUIT
1.24V
REF
* ALWAYS CONNECT E1 TO GROUND PIN ON MiniDIP PACKAGE.
EMITTERS TIED TO GROUND ON TO-220 PACKAGE.
0.15V
GND
1082 BD
U
OPERATIO
The LT1082 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
reachesapredeterminedlevel. Controlofoutputvoltageis
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 mid-frequencies 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
pulse-by-pulsecurrentlimitingtoprovidemaximumswitch
protection under output overload or short conditions. A
low dropout internal regulator provides a 2.3V supply for
all internal circuitry on the LT1082. This low dropout
design allows input voltage to vary from 3V to 75V with
virtually no change in device performance. A 60kHz
oscillator is the basic clock for all internal timing. It turns
“on” the output switch via the logic and driver circuitry.
Special adaptive anti-sat 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 and
with IFB of 60µA to 200µA, it programs the LT1082 to
7
LT1082
U
OPERATIO
only 120µA supply current for shutdown circuitry biasing.
disconnect the main error amplifier output and connects
theoutputoftheflybackamplifiertothecomparatorinput.
TheLT1082willthenregulatethevalueoftheflybackpulse
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
voltagecanberegulatedwithnodirectconnectionbetween
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 LT1082
ignorestheleakageinductancespikeattheleadingedgeof
the flyback pulse to improve output regulation.
See AN19 for full application details.
Extra Pins on the MiniDIP Packages
The miniDIP LT1082 has the emitters of the power
transistor brought out separately from the ground pin.
Thiseliminateserrorsduetogroundpinvoltagedropsand
allows the user to reduce switch current limit by a factor
of 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.”
When IFB drawn out of the FB pin reaches 350µA, the
LT1082 shifts the switching frequency down to 12kHz.
This unique feature provides high voltage short-circuit
protection in systems like the telecom 5V supplies with
input voltages down to –70V; lower frequency is needed
undershort-circuitconditionswithcurrentmodeswitchers
because minimum “on” time cannot be forced below the
internally set blanking time. Referring to the telecom 5V
supply circuit on the front page, with output shorted to
ground, the VFB stays at 0.6V when sourcing IFB up to
1mA. If the FB pin is forced to source more than 1mA, the
frequency shifting function may be defeated. Therefore,
the minimum suggested value for RFB is 1k and the
maximum suggested value is 1.2k. Also, no capacitance
more than 1nF should be used on the FB pin, because it
may cause unstable switching frequency in this low
frequency mode.
Thermal Considerations When Using the
MiniDIP Packages
The low supply current and high switch efficiency of the
LT1082 allow it to be used without a heat sink in most
applications when the TO-220 package is selected.
This package is rated at 50°C/W. The miniDIPs,however,
are rated at 100°C/W in ceramic (J) and 90°/W in plastic
(N).
Care should be taken for miniDIP applications to ensure
thattheworstcaseinputvoltageandloadcurrentconditions
do not cause excessive die temperatures. The following
formulascanbeusedasaroughguidetocalculateLT1082
power dissipation. For more details, the reader is referred
to Application Note 19 (AN19), “Efficiency Calculations”
section.
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
limitadjustment,softstarting,andtotalregulatorshutdown.
Duringnormalregulatoroperationthispinsitsatavoltage
between 0.9V (low output current) and 2V (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 LT1082 in an idle mode. Pulling the VC
pin below 0.15V causes total regulator shutdown, with
Average supply current (including driver current) is:
IIN ≈ 4.5mA + ISW (0.004 + DC/28)
ISW = switch current
DC = switch duty cycle
Switch power dissipation is given by:
PSW = (ISW)2 • RSW • DC
RSW = LT1082 switch “on” resistance (1.2Ω maximum)
8
LT1082
U
OPERATIO
Total power dissipation is the sum of supply current times
input voltage plus switch power:
LT1082 Synchronizing
The LT1082 can be externally synchronized in the fre-
quency range of 75kHz to 90kHz. This is accomplished as
shown in the accompanying figures. Synchronizing oc-
curs 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 ≈
0.6µs. The effect of a synchronizing pulse on the LT1082
amplifier offset can be calculated from:
PTOT = (IIN)(VIN) + PSW
In a typical example, using negative-to-positive converter
to generate 5V at 0.5A from a –45V input, duty cycle is
approximately 12%, and switch current is about 0.5A,
yielding:
IIN = 4.5mA + 0.5(0.004 + DC/28) = 8.7mA
PSW = (0.5)2 • 1.2Ω • (0.12) = 0.036W
P
TOT = (45V)(8.7mA) + 0.036 = 0.43W
KT
q
V
C
R3
t
f
I +
( )( )
S
S C
Temperature rise in a plastic miniDIP would be 90°C/W
times 0.43W, or approximately 39°C. The maximum am-
bient temperature would be limited to 100°C (commercial
temperature limit) minus 39°C, or 61°C.
∆V
=
OS
I
C
KT/q = 26mV at 25°C
tS = pulse width
fS = pulse frequency
IC = LT1082 VC source current (≈ 200µA)
VC = LT1082 operating VC voltage (1V to 2V)
R3 = resistor used to set mid-frequency “zero” in LT1082
frequency compensation network.
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 LT1082 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 noncritical applications
withtemporaryoverloads.Asecondapproachistousethe
largerTO-220(T)packagewhich,evenwithoutaheatsink,
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.
With tS = 0.6µs, fS = 80kHz, VC = 1.5V, and R3 = 2k, offset
voltageshiftis≈ 5mV. Thisisnotparticularlybothersome,
but note that high offset 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 100mV of ground to
ensure synchronizing.
The third approach for lower current applications is to
leave the second switch emitter (miniDIP only) 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.
Synchronizing the LT1082
V
IN
LT1082
GND
V
C
ThefourthapproachistoclamptheVC pintoavoltageless
than its internal clamp level of 2V. The LT1082 switch
current limit is zero at approximately 1V on the VC pin and
1.6A at 2V on the VC pin. Peak switch current can be
externally clamped between these two levels with a diode.
See AN19 for details.
C2
D1
350pF
1N4148
R3
C1
VN2222*
R2
2.2k
D2
1N4148
FROM 5V
LOGIC
*SILICONIX OR EQUIVALENT
1082 OP01
9
LT1082
U
O
TYPICAL APPLICATI S
Totally Isolated Converter
MUR110
1.24:1
15V
AT 0.3A
+
+
25V
200µF
200µF
1
L
PRI
500µH
COM
1
MUR110
V
IN
–15V
AT 0.3A
+
V
IN
V
SW
FB
25µF
30V
MUR110
to 70V
LT1082
GND
V
C
3k
MINIMUM LOAD OF 0.15A IS REQUIRED
FOR EACH OUTPUT. (SEE AN19)
0.01µF
7k
1082 TA03
Boost Converter
1mH, 1A
MUR110
V
IN
VOUT
90V AT 120mA
15V
78.8k
V
IN
V
SW
LT1082
GND
+
+
FB
25µF
100µF
V
C
4.7k
0.033µF
1.1k
0.22µF
1082 TA04
10
LT1082
U
PACKAGE DESCRIPTIO Dimensions in inches (milimeters) unless otherwise noted.
J8 Package
8-Lead Ceramic DIP
CORNER LEADS OPTION
0.200
(5.080)
MAX
(4 PLCS)
0.290 – 0.320
(7.366 – 8.128)
0.405
(10.287)
MAX
0.005
(0.127)
MIN
0.023 – 0.045
(0.58 – 1.14)
HALF LEAD
OPTION
0.015 – 0.060
(0.381 – 1.524)
6
5
4
8
7
0.045 – 0.065
0.008 – 0.018
(0.203 – 0.460)
(1.14 – 1.65)
FULL LEAD
OPTION
0.025
(0.635)
RAD TYP
0.220 – 0.310
(5.588 – 7.874)
0° – 15°
0.045 – 0.065
(1.14 – 1.65)
0.385 ± 0.025
(9.779 ± 0.635)
0.125
3.175
MIN
1
2
3
0.100 ± 0.010
0.014 – 0.026
(2.540 ± 0.254)
(0.360 – 0.660)
N8 Package
8-Lead Plastic DIP
0.400
(10.160)
MAX
0.130 ± 0.0
(3.302 ± 0.127)
0.300 – 0.320
(7.620 – 8.128)
0.045 – 0.065
(1.143 – 1.651)
8
1
7
6
5
4
0.065
(1.651)
TYP
0.250 ± 0.010
(6.350 ± 0.254)
0.009 – 0.015
(0.229 – 0.381)
0.125
0.020
(0.508)
MIN
(3.175)
MIN
+0.025
–0.015
2
3
0.045 ± 0.015
0.325
(1.143 ± 0.381)
0.100 ± 0.010
(2.540 ± 0.254)
+0.635
8.255
(
)
–0.381
0.018 ± 0.003
(0.457 ± 0.076)
Q Package
5-Lead Plastic DD
0.401 ± 0.015
(10.185 ± 0.381)
0.060
(1.524)
0.175 ± 0.008
(4.445 ± 0.203)
0.050 ± 0.008
(1.270 ± 0.203)
15° TYP
+0.008
0.004
+0.012
–0.020
+0.305
–0.508
0.331
–0.004
0.059
(1.499)
TYP
+0.203
–0.102
0.102
(
)
8.407
(
)
0.105 ± 0.008
(2.667 ± 0.203)
0.067 ± 0.010
(1.702 ± 0.254)
0.050 ± 0.012
(1.270 ± 0.305)
+0.012
–0.020
+0.305
–0.508
0.022 ± 0.005
(0.559 ± 0.127)
0.143
0.032 ± 0.008
(0.813 ± 0.203)
3.632
(
)
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LT1082
U
PACKAGE DESCRIPTIO Dimensions in inches (milimeters) unless otherwise noted.
T Package
5-Lead TO-220
0.380 – 0.420
(9.652 – 10.668)
0.169 – 0.185
(4.293 – 4.699)
0.079 – 0.135
(2.007 – 3.429)
0.035 – 0.055
(0.889 – 1.397)
0.139 – 0.153
(3.531 – 3.886)
DIA
0.560 – 0.650
(14.224 – 16.510)
0.460 – 0.500
(11.68 – 12.70)
0.620 ± 0.020
(15.75 ± 0.508)
0.866 – 0.913
(21.996 – 23.190)
0.700 – 0.728
(17.780 – 18.491)
0.970 – 1.050
(24.64 – 26.67)
0.055 – 0.090
(1.397 – 2.286)
0.015 – 0.025
(0.381 – 0.635)
0.079 – 0.115
(2.007 – 2.921)
0.210 – 0.240
(5.334 – 6.096)
0.057 – 0.077
(1.448 – 1.956)
0.028 – 0.035
(0.711 – 0.889)
T5 (FORMED) 0392
LT/GP 0193 10K REV 0
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
12
●
●
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LINEAR TECHNOLOGY CORPORATION 1993
相关型号：
LT1083CK#TR
IC VREG 1.2 V-15 V ADJUSTABLE POSITIVE LDO REGULATOR, 1.5 V DROPOUT, MBFM2, METAL CAN, TO-3, 2 PIN, Adjustable Positive Single Output LDO Regulator
Linear
LT1083CK(ADJ)
Adjustable Positive LDO Regulator, 1.2V Min, 1.5V Dropout, MBFM2, HERMETIC SEALED, TO-3, 2 PIN
SEMTECH
LT1083CK-3.3
Fixed Positive LDO Regulator, 3.3V, 1.5V Dropout, MBFM2, HERMETIC SEALED, TO-3, 2 PIN
SEMTECH
©2020 ICPDF网 联系我们和版权申明