Transcript
LT1082 1A High Voltage, Efficiency Switching Voltage Regulator DESCRIPTIO U
FEATURES ■ ■ ■ ■ ■
■ ■ ■
Wide Input Voltage Range: 3V to 75V High Switch Voltage: 100V 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
The LT®1082 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.
Telecom 5V Supply at 0.7A from –48V 90V Supply at 120mA from 15V All Applications Using LT1072 (See Below for Specification Differences)
An externally activated shutdown mode reduces total supply current to 120µA typical for standby operation. Totally isolated and regulated outputs can be generated by using the optional “isolated flyback regulation mode” built into the LT1082, without the need for optocouplers or extra transformer windings.
U APPLICATIO S ■ ■ ■
LT1082 and LT1072 Major Specification Differences LT1082C LT1072HV 3V to 75V 3V to 60V 100V 75V 1A 1.25A 4.5mA 6mA 60kHz 40kHz 16.2 + 0.6 (35kΩ/RFB) 16 + 0.35 (7kΩ/RFB)
VIN VSW Switch Current Limit Quiescent Current Operating Frequency Flyback Reference Voltage
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. A complete design manual (AN19) and Switcher CAD (LTC Switching Power Supply Design 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.
The LT1082 operates with supply voltages from 3V to 75V, switch voltage up to 100V and draws only 4.5mA quiescent current. It can deliver load power up to 20W with no external power devices. By utilizing current-mode switching techniques, it provides excellent AC and DC load and line regulation.
The LT1082 has a unique feature to provide high voltage short-circuit protection. When the FB pin is pulled down to 0.6V and the current out of the pin reaches approximately 350µA, the switching frequency will shift down from 60kHz to 12kHz. The LT1082 is nearly identical to the lower voltage LT1072. For the major differences in specifications, see the table on the left. , LTC and LT are registered trademarks of Linear Technology Corporation
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TYPICAL APPLICATIO
Telecom 5V Supply Maximum Output Current vs Input Voltage
Negative-to-Positive Telecom 5V Supply **250µH
*D1
3.83k VIN 33µF 80V CHEMI-CON SXE SERIES
+
VSW
Q1 2N5401
470µF 10V CHEMI-CON SXE SERIES
LT1082 GND
FB
VC
1.1k 4.7k 0.01µF 0.22µF –20V TO –70V
+
VOUT 5V, 0.7A
1082 TA01
* MOTOROLA MUR110 (100V, 1A) ** 69 TURNS OF #28 AWG WIRE ON A MICROMETALS T60 TYPE 52 CORE. 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.
NOTE: MAXIMUM OUTPUT CURRENT IS A FUNCTION OF INPUT VOLTAGE. SEE THE GRAPH ON THE RIGHT.
1.0
MAXIMUM OUTPUT CURRENT (A)
■
0.9 0.8
f = 45kHz ISW LIMIT = 1.07A
L=550µH L=450µH L=350µH L=250µH
0.7 0.6
L=150µH
0.5 L=100µH 0.4 0 –10 –20 –30 –40 –50 –60 –70 –80 –90 INPUT VOLTAGE (V) 1082 TA02
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LT1082 W W
W
AXI U
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ABSOLUTE
RATI GS
(Note 1)
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 (OBSOLETE) ............... – 55°C to 150°C LT1082I ........................................... – 40°C to 125°C LT1082C ............................................... 0°C to 100°C
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PACKAGE/ORDER I FOR ATIO TOP VIEW GND 1
8
E2
VC 2
7
VSW
FB 3
6
E1
NC 4
5
VIN
FRONT VIEW 5 4 3 2 1
ORDER PART NUMBER LT1082CN8 LT1082IN8
VIN VSW GND FB VC
5 4 3 2 1
Q PACKAGE 5-LEAD DD
N8 PACKAGE 8-LEAD PLASTIC DIP
TJMAX = 100°C, θJA = 90°C/W (CN8) TJMAX = 125°C, θJA = 90°C/W (IN8)
FRONT VIEW
TJMAX = 100°C, θJA = 40°C/ W (CQ) TJMAX = 125°C, θJA = 40°C/ W (IQ)
VIN VSW GND FB VC
T PACKAGE 5-LEAD TO-220 TJMAX = 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.
ORDER PART NUMBER
ORDER PART NUMBER
LT1082CQ LT1082IQ
LT1082CT LT1082IT
J8 PACKAGE 8-LEAD CERAMIC DIP TJMAX = 150°C, θJA = 100°C/W (MJ8)
LT1082MJ8
OBSOLETE PACKAGE Consider the Q Package for Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VC = 0.5V, VFB = VREF, output pin open, unless otherwise specified. SYMBOL
PARAMETER
CONDITIONS
MIN
VREF
Reference Voltage
Measured at Feedback Pin VC = 0.8V
1.224 1.244 1.214 1.244
IB
Feedback Input Current
●
VFB = VREF
TYP
MAX
UNITS
1.264 1.274
V V
350
750 1100
nA nA
●
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
Minimum Input Voltage
3000 2400
4400
●
6000 7000
µmho µmho
150 120
200
●
400 400
µA µA
2.3 0.36
V V
0.03
%/V
1.8 0.12
0.22
●
350 ●
650 2.6
V/V 3.0
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LT1082
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VC = 0.5V, VFB = VREF, output pin open, unless otherwise specified. SYMBOL IQ
PARAMETER
CONDITIONS
MIN
Supply Current
3V ≤ VIN ≤ VMAX, VC = 0.6V
Control Pin Threshold
Duty Cycle = 0 ●
Normal/Flyback Threshold on Feedback Pin f
Switching Frequency ●
Output Switch Breakdown Voltage
3V ≤ VIN ≤ VMAX, ISW = 1.5mA
Flyback Reference Voltage
7.0
0.9
1.1 1.25
●
●
VSAT ILIM
60µA ≤ IFB ≤ 200µA
Flyback Reference Voltage Line Regulation
IFB = 60µA, 3V ≤ VIN ≤ VMAX
mA V V
0.58
0.67
0.8
V
50 45
60
70 75
kHz kHz
12
IFB = 60µA
Change in Flyback Reference Voltage
UNITS
4.5
100
Control Voltage to Switch Current Transconductance VFB
MAX
0.7 0.5
800µA ≥ IFB ≥ 450µA BV
TYP
17 16 3.5
kHz
115
V
1.5
A/V
18.6
20.5 21.5
V V
4.6
6.5
V
0.01
0.03
%/V
150
300
500
µmho
15 30
32 50
70 90
µA µA
0.8
Flyback Amplifier Transconductance (gm)
∆IC = ±10µA
Flyback Amplifier Source and Sink Current
VC = 0.6V Source IFB = 60µA Sink
● ●
Output Switch “On” Resistance (Note 2) Switch Current Limit (LT1082C)
ISW = 0.7A (LT1082C), ISW = 0.5A (LT1082M) Duty Cycle = 20% Duty Cycle ≤ 50% Duty Cycle = 80% (Note 3)
● ● ● ●
1.07 1.0 0.8
1.2 2.6 2.6 2.4
Ω A A A
Switch Current Limit (LT1082I)
Duty Cycle = 20% Duty Cycle ≤ 50% Duty Cycle = 80% (Note 3)
● ● ●
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 3)
● ● ●
0.75 0.7 0.6
3.0 3.0 2.8
A A A
35
45
mA/A
92
97
%
350 250 300
µA mV mV
∆IIN ∆ISW
Supply Current Increase During Switch-On Time
DCMAX
Maximum Switch Duty Cycle
85
Flyback Sense Delay Time Shutdown Mode Supply Current Shutdown Mode Threshold Voltage
µs
1.5 3V ≤ VIN ≤ VMAX, VC = 0.05V 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.
●
70 50
120 150
Note 3: For duty cycles (DC) between 50% and 80%, minimum guaranteed switch current decreases linearly.
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TYPICAL PERFOR A CE CHARACTERISTICS Suggested Core Size and Inductance for Telecom 5V Supply
Telecom 5V Supply Short-Circuit Frequency Shift-Down
Telecom 5V Supply Efficiency
KOOL Mµ OR MOLYPERMALLOY
100mA
T38 250µH
T38 200µH
200mA
T50 250µH
T38 150µH
400mA
T60 250µH
T50 150µH
600mA
T60 250µH
T50 200µH
800mA
T80 350µH
T80 350µH
80
79
TA = 25°C 76
70
VIN = –20V
60
73
1082 GA
FREQUENCY (kHz)
TYPE 52 POWDERED IRON
EFFICIENCY (%)
LOAD CURRENT
VIN = –40V
70 67
VIN = –60V
64
50 40 30 20
61 VIN = –70V
58
L = 250µH R = 0.08Ω
10 0
55 0
2
1
3
4
6
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 100mW HIGHER. 1082 G01
Short-Circuit Frequency Shift-Down vs Feedback Current
SWITCH CURRENT (A)
FREQUENCY (kHz)
96
40 30 20
3
95
2
TJ = –55°C
TJ = 25°C
94 93 92
TJ = 150°C
1
91
10 0
0
100 200 300 400 500 600 700 800 FEEDBACK CURRENT (µA)
0
90 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C)
10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%)
1082 G05
1082 G04
1082 G03
Flyback Blanking Time
Switch Saturation Voltage
Minimum Input Voltage 2.9
2.0
2.8
MINIMUM INPUT VOLTAGE (V)
2.2
1.8 1.6 1.4 1.2 1.0 –75 –50 –25 0 25 50 75 100 125 150 JUNCTION TEMPERATURE (°C) 1082 G06
2.00 SWITCH SATURATION VOLTAGE (V)
0
TIME (µs)
0
97
TA = – 55°C
TA = 150°C
50
1
Maximum Duty Cycle
Switch Current Limit
DUTY CYCLE (%)
TA = 0°C
60
4 3 2 OUTPUT VOLTAGE (V)
1082 G02
4
70
5
ISW = 1A
2.7 ISW = 0A 2.6 2.5 2.4 2.3 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C) 1082 G07
1.75 TJ = 150°C 1.50
TJ = 100°C TJ = 25°C
1.25 1.00 0.75
TJ = –50°C
0.50 0.25 0 0
0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 SWITCH CURRENT (A) 1082 G08
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TYPICAL PERFOR A CE CHARACTERISTICS Reference Voltage and Switching Frequency vs Temperature
Isolated Mode Flyback Reference Voltage
Line Regulation 1.250
5
24 RFB = 3k FREQUENCY (kHz)
21 RFB = 6k
19
RFB = 10k
18
FREQ
60
17
1.245
1.240
55
1.235
50
1.230
16 45 1.225 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C)
15 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C)
Feedback Bias Current vs Temperature
2 1
–1 –2
200
700
725 FEEDBACK PIN VOLTAGE (AT THRESHOLD) 700
–22
180
–20
160
675
–18
650
–16
625
–14
600
–12
575 FEEDBACK PIN CURRENT (AT THRESHOLD) 550
–10 –8
40
525
–6
20
500 –4 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C)
0
VC PIN VOLTAGE (mV)
200 100 0 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 1082 G12
14
90
13
70 60 50 40 30 20
40
0
0
10
20 30 40 50 60 SUPPLY VOLTAGE (V)
70
80
1082 G15
80 60
0
10 20 30 40 50 60 70 80 90 100 VC PIN VOLTAGE (mV)
11 10
90% DUTY CYCLE
9 8
50% DUTY CYCLE
7
10% DUTY CYCLE
6 5
0% DUTY CYCLE
4
10
0
100
12
SUPPLY CURRENT (mA)
DRIVER CURRENT (mA)
VC = 0V
80
TJ = 150°C
120
Supply Current vs Input Voltage**
100
80
160
120
140
1082 G17
Driver Current* vs Switch Current
200
80
–55°C ≤ TJ ≤ 125°C
1082 G16
Supply Current vs Supply Voltage (Shutdown Mode)
VC = 50mV
70
30 40 50 60 INPUT VOLTAGE (V)
Shutdown Mode Supply Current –24
300
20
10
1082 G10
750
400
TJ = 25°C
–4
800
500
TJ = 150°C
–3
Normal/Feedback Mode Threshold on Feedback Pin
600
TJ = –55°C
0
0
VC PIN CURRENT (µA)
FEEDBACK BIAS CURRENT (nA)
3
1082 G11
1082 G09
SUPPLY CURRENT (µA)
4
–5
SUPPLY CURRENT (µA)
FLYBACK VOLTAGE (V)
22
20
VREF
65
REFERENCE VOLTAGE (V)
23
REFERENCE VOLTAGE CHANGE (mV)
70
25
3 2
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A)
* AVERAGE SUPPLY CURRENT = IQ + DC(2.9 + 10 –2 ISW + 10 –5 ISW2) IQ = QUIESCENT CURRENT, DC = DUTY CYCLE, 1082 G13 ISW = SWITCH CURRENT
0
10
20
60 40 50 30 INPUT VOLTAGE (V)
70
80
**UNDER VERY LOW OUTPUT CURRENT CONDITIONS, DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH 1082 G14 10% OR LESS. sn1082 1082fas
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TYPICAL PERFOR A CE CHARACTERISTICS
gm =
4000
400
–400
10
350
–350
9
CURRENT (OUT OF VC PIN)
300
VC VOLTAGE (mV)
3500 3000 2500 2000 1500
–300
250
–250
200
–200 VOLTAGE AT VC PIN
150
–150
100
–100
50
–50
VC CURRENT (µA)
TRANSCONDUCTANCE (µmho)
4500
∆I (VC PIN) ∆V (FB PIN)
IDLE SUPPLY CURRENT (mA)
5000
Idle Supply Current vs Temperature
Shutdown Thresholds
Error Amplifier Transconductance
1000 500 0 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C)
8 7 6 5
VIN = 75V
4
VIN = 3V
3 2
0 0 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C)
1 –75 –50 –25 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 1082 G20
1082 G19
1082 G18
Feedback Pin Clamp Voltage
Switch “Off” Characteristics
800
500 A. VIN = 3V B. VIN = 15V C. VIN = 40V D. VIN = 55V E. VIN = 75V
450 700
400
TJ = –55°C
SWITCH CURRENT (µA)
FEEDBACK VOLTAGE (mV)
VC = 0.6V
600 TJ = 25°C 500
TJ = 150°C
400
350 300 250 200 150
A
B
C
D
E
100
300
50 200
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 FEEDBACK CURRENT (mA)
0
10 20 30 40 50 60 70 80 90 100 SWITCH VOLTAGE (V)
1082 G21
1082 G22
Transconductance of Error Amplifier
VC Pin Characteristics 7000
400 TJ = 25°C TRANSCONDUCTANCE (µmho)
6000
VFB = 1.5V (CURRENT INTO VC PIN)
200 100 0 –100
VFB = 0.8V (CURRENT OUT OF VC PIN)
–200 –300
5000
30 gm
4000
0
0.5
1.5 2.0 1.0 VC PIN VOLTAGE (V)
2.5 1082 G23
60
3000
90
2000
120
1000
150
0
180
–1000
–400
0
θ
1k
10k
100k 1M FREQUENCY (Hz)
PHASE (DEG)
VC PIN CURRENT (µA)
300
–30
210 10M 1082 G24
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LT1082 W
BLOCK DIAGRA
VIN
16.2V
SWITCH OUT
FLYBACK ERROR AMP
2.3V REG
OSC 60kHz 14kHz
LOGIC
DRIVER
ANTI-SAT
MODE SELECT COMP
–
FB
+
ERROR + AMP
VC
CURRENT AMP GAIN ≈ 5
– E1* E2
SHUTDOWN CIRCUIT 1.24V REF
0.2Ω
0.2Ω
0.15V
GND
* ALWAYS CONNECT E1 TO GROUND PIN ON MiniDIP PACKAGE. EMITTERS TIED TO GROUND ON TO-220 PACKAGE.
1082 BD
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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 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 mid-frequencies in the energy storage inductor. This greatly simplifies closedloop frequency compensation under widely varying input voltage or output load conditions. Finally, it allows simple pulse-by-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 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 sn1082 1082fas
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LT1082
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OPERATIO
disconnect the main error amplifier output and connects the output of the flyback amplifier to the comparator input. The LT1082 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 LT1082 ignores the leakage inductance spike at the leading edge of the flyback pulse to improve output regulation. 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 under short-circuit conditions with current mode switchers 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. 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 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
only 120µA supply current for shutdown circuitry biasing. 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. This eliminates errors due to ground pin voltage drops and 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.” 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 that the worst case input voltage and load current conditions do not cause excessive die temperatures. The following formulas can be used as a rough guide to calculate LT1082 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 ≈ 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) sn1082 1082fas
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OPERATIO
Total power dissipation is the sum of supply current times input voltage plus switch power: 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
LT1082 Synchronizing The LT1082 can be externally synchronized in the frequency range of 75kHz to 90kHz. 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 ≈ 0.6µs. The effect of a synchronizing pulse on the LT1082 amplifier offset can be calculated from:
PTOT = (45V)(8.7mA) + 0.036 = 0.43W Temperature rise in a plastic miniDIP would be 90°C/W times 0.43W, or approximately 39°C. The maximum ambient temperature would be limited to 100°C (commercial temperature limit) minus 39°C, or 61°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 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 with temporary overloads. A second approach is to use the larger TO-220 (T) 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 (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.
∆VOS
KT VC + t f I S S C R3 q = IC
( )( )
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. With tS = 0.6µs, fS = 80kHz, VC = 1.5V, and R3 = 2k, offset voltage shift is ≈ 5mV. This is not particularly bothersome, 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. Synchronizing the LT1082 VIN LT1082 GND
The fourth approach is to clamp the VC pin to a voltage less 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.
VC
D1 1N4148
R3
C2 350pF
VN2222* C1
R2 2.2k
D2 1N4148
*SILICONIX OR EQUIVALENT
FROM 5V LOGIC
1082 OP01
sn1082 1082fas
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LT1082 UO
TYPICAL APPLICATI
S Totally Isolated Converter MUR110
1.24:1 25V
MUR110
15V AT 0.3A
+ 200µF 1
LPRI 500µH
COM
1
+ 200µF
VIN
+
VIN 30V to 70V
–15V AT 0.3A
VSW
25µF
MUR110
LT1082 FB GND
VC 3k 0.01µF
MINIMUM LOAD OF 0.15A IS REQUIRED FOR EACH OUTPUT. (SEE AN19)
7k
1082 TA03
Boost Converter 1mH, 1A
VIN 15V
VIN
MUR110
VOUT 90V AT 120mA 78.8k
VSW
LT1082
+
+
FB
25µF
GND
100µF
VC
4.7k
0.033µF
1.1k
0.22µF
1082 TA04
U
PACKAGE DESCRIPTIO
J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) 0.405 (10.287) MAX
(Reference LTC DWG # 05-08-1110) 0.300 BSC (0.762 BSC)
0.008 – 0.018 (0.203 – 0.457)
0.200 (5.080) MAX
CORNER LEADS OPTION (4 PLCS)
0° – 15°
0.023 – 0.045 (0.584 – 1.143) HALF LEAD OPTION 0.045 – 0.068 (1.143 – 1.727) FULL LEAD OPTION
NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS
0.015 – 0.060 (0.381 – 1.524)
0.005 (0.127) MIN
8
0.014 – 0.026 (0.360 – 0.660)
0.100 (2.54) BSC
6
5
0.025 (0.635) RAD TYP
0.220 – 0.310 (5.588 – 7.874)
1 0.045 – 0.065 (1.143 – 1.651)
7
2
3
4
0.125 3.175 MIN J8 1298
OBSOLETE PACKAGE sn1082 1082fas
10
LT1082 U
PACKAGE DESCRIPTIO
N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510)
0.300 – 0.325 (7.620 – 8.255)
0.130 ± 0.005 (3.302 ± 0.127)
0.045 – 0.065 (1.143 – 1.651)
0.065 (1.651) TYP
0.009 – 0.015 (0.229 – 0.381)
(
0.400* (10.160) MAX 8
7
6
5
1
2
3
4
0.255 ± 0.015* (6.477 ± 0.381)
+0.035 0.325 –0.015 +0.889 8.255 –0.381
)
0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003
0.100 (2.54) BSC
(0.457 ± 0.076)
N8 1098
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
Q Package 5-Lead Plastic DD Pak (Reference LTC DWG # 05-08-1461)
.256 (6.502)
.060 (1.524) TYP
.060 (1.524)
.390 – .415 (9.906 – 10.541)
.165 – .180 (4.191 – 4.572)
.045 – .055 (1.143 – 1.397)
15° TYP .060 (1.524)
.183 (4.648)
+.008 .004 –.004 +0.203 0.102 –0.102
.059 (1.499) TYP
.330 – .370 (8.382 – 9.398)
(
)
.095 – .115 (2.413 – 2.921)
.075 (1.905) .300 (7.620)
+.012 .143 –.020 +0.305 3.632 –0.508
(
BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK
.067 (1.702) .028 – .038 BSC (0.711 – 0.965) TYP
)
Q(DD5) 0502
.420 .276
.080
.420
.050 ± .012 (1.270 ± 0.305)
.013 – .023 (0.330 – 0.584)
.325
.350 .205
.565
.565
.320 .090
.090 .067
.042
RECOMMENDED SOLDER PAD LAYOUT NOTE: 1. DIMENSIONS IN INCH/(MILLIMETER) 2. DRAWING NOT TO SCALE
.067
.042
RECOMMENDED SOLDER PAD LAYOUT FOR THICKER SOLDER PASTE APPLICATIONS
sn1082 1082fas
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.
11
LT1082 U
PACKAGE DESCRIPTIO
T Package 5-Lead Plastic TO-220 (Standard) (Reference LTC DWG # 05-08-1421) 0.165 – 0.180 (4.191 – 4.572)
0.147 – 0.155 (3.734 – 3.937) DIA
0.390 – 0.415 (9.906 – 10.541)
0.045 – 0.055 (1.143 – 1.397)
0.230 – 0.270 (5.842 – 6.858) 0.570 – 0.620 (14.478 – 15.748)
0.460 – 0.500 (11.684 – 12.700)
0.620 (15.75) TYP
0.330 – 0.370 (8.382 – 9.398)
0.700 – 0.728 (17.78 – 18.491)
0.095 – 0.115 (2.413 – 2.921)
SEATING PLANE 0.152 – 0.202 0.260 – 0.320 (3.861 – 5.131) (6.60 – 8.13)
0.155 – 0.195* (3.937 – 4.953) 0.013 – 0.023 (0.330 – 0.584)
BSC
0.067 (1.70)
0.028 – 0.038 (0.711 – 0.965)
0.135 – 0.165 (3.429 – 4.191)
* MEASURED AT THE SEATING PLANE T5 (TO-220) 0399
RELATED PARTS PART NUMBER
DESCRIPTION
COMMENTS
LT1765
1.25MHz, 3A, Step-Down Regulator
VIN: 3V to 25V, VREF = 1.2V, SO8 Package
LT1767
1.25MHz, 1.25A, Step-Down Regulator
VIN: 3V to 25V, VREF = 1.2V, MSOP-8 Package
LTC3401
3MHz, 1A, Step-Up Regulator
VIN: 0.5V to 5V, MSOP-10 Package
LTC3404
1.4MHz, IOUT = 600mA, Step-Down Regulator
VIN: 2.65V to 6V, VREF = 0.8V, MSOP-8 Package
LTC3411
2MHz, 1.25A, Step-Down Regulator
VIN: 2.5V to 5.5V, VREF = 0.8V, MSOP-10, TSSOP-16E Package
sn1082 1082fas
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Linear Technology Corporation
LT/CPI 0202 1.5K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
LINEAR TECHNOLOGY CORPORATION 1993
