LT1073CS8-5#TR [Linear]
LT1073 - Micropower DC-DC Converter Adjustable and Fixed 5V, 12V; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C;
| 型号： | LT1073CS8-5#TR |
| 厂家： | 
Linear |
| 描述： | LT1073 - Micropower DC-DC Converter Adjustable and Fixed 5V, 12V; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C 开关 光电二极管 |
| 文件： | 总16页 (文件大小：250K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1073
Micropower
DC/DC Converter
Adjustable and Fixed 5V, 12V
U
FEATURES
DESCRIPTIO
The LT®1073 is a versatile micropower DC/DC converter.
The device requires only three external components to
deliver a fixed output of 5V or 12V. The very low minimum
supply voltage of 1V allows the use of the LT1073 in
applications where the primary power source is a single
cell. An on-chip auxiliary gain block can function as a low-
battery detector or linear post-regulator.
■
No Design Required
■
Operates at Supply Voltages from 1V to 30V
■
Consumes Only 95µA Supply Current
Works in Step-Up or Step-Down Mode
■
■
Only Three External Off-the-Shelf Components
Required
■
Low-Battery Detector Comparator On-Chip
■
User-Adjustable Current Limit
Internal 1A Power Switch
Average current drain of the LT1073-5 used as shown in
the Typical Application circuit below is just 135µA un-
loaded, making it ideal for applications where long battery
life is important. The circuit shown can deliver 5V at 40mA
from an input as low as 1.25V and 5V at 10mA from a 1V
input.
■
■
Fixed or Adjustable Output Voltage Versions
■
Space-Saving 8-Pin PDIP or SO-8 Package
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APPLICATIO S
■
Pagers
Cameras
Single-Cell to 5V Converters
Battery Backup Supplies
Laptop and Palmtop Computers
Cellular Telephones
Portable Instruments
The device can easily be configured as a step-up or step-
down converter, although for most step-down applica-
tions or input sources greater than 3V, the LT1173 is
recommended. Switch current limiting is user-adjustable
by adding a single external resistor. Unique reverse-
battery protection circuitry limits reverse current to safe,
nondestructive levels at reverse supply voltages up to
1.6V.
■
■
■
■
■
■
■
4mA to 20mA Loop Powered Instruments
■
Hand-Held Inventory Computers
■
Battery-Powered α, β, and γ Particle Detectors
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
Single Alkaline “AA” Cell Operating
Hours vs DC Load Current
1000
Single-Cell to 5V Converter
CADDELL-BURNS
7300-12
1N5818
82µH
5V
40mA
100
2
1
I
V
LIM
IN
3
8
SW1
LT1073-5
L = 180µH
1.5V
AA CELL*
10
SENSE
+
100µF
SANYO
0S-CON
GND
5
SW2
4
L = 82µH
1
1
10
100
OPERATES WITH CELL VOLTAGE ≥1V
ADD 10µF DECOUPLING CAPACITOR IF
LOAD CURRENT (mA)
*
LT1073 TA02
BATTERY IS MORE THAN 2" AWAY FROM LT1073
1073 TA01
1
LT1073
W W U W
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W
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ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
ORDER PART
Supply Voltage, Step-Up Mode................................ 15V
Supply Voltage, Step-Down Mode ........................... 36V
SW1 Pin Voltage...................................................... 50V
SW2 Pin Voltage........................................... –0.4 to VIN
Feedback Pin Voltage (LT1073) ................................. 5V
Switch Current........................................................ 1.5A
Maximum Power Dissipation ............................. 500mW
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
NUMBER
I
1
2
3
4
FB (SENSE)*
8
7
6
5
LIM
LT1073CN8
LT1073CN8-5
LT1073CN8-12
LT1073CS8
LT1073CS8-5
V
SET
A0
IN
SW1
SW2
GND
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
LT1073CS8-12
S8 PART MARKING
*FIXED VERSIONS
TJMAX = 125°C, θJA = 100°C/W (N8)
JMAX = 125°C, θJA = 120°C/W (S8)
T
1073
10735
107312
Consult factory 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 = 1.5V unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
Switch Off
No Load
MIN
TYP
MAX
UNITS
I
I
Quiescent Current
●
●
95
130
µA
Q
Q
Quiescent Current, Step-Up
Mode Configuration
LT1073-5
LT1073-12
135
250
µA
µA
V
V
Input Voltage
Step-Up Mode
1.15
1.0
12.6
12.6
V
V
IN
Step-Down Mode
LT1073 (Note 2)
●
●
30
V
Comparator Trip Point Voltage
Output Sense Voltage
202
212
222
mV
LT1073-5 (Note 3)
LT1073-12 (Note 3)
●
●
4.75
11.4
5
12
5.25
12.6
V
V
OUT
Comparator Hysteresis
Output Hysteresis
LT1073
●
5
10
mV
LT1073-5
LT1073-12
●
●
125
300
250
600
mV
mV
f
Oscillator Frequency
Duty Cycle
●
●
●
●
●
●
15
65
30
19
72
23
80
kHz
%
OSC
DC
Full Load (V = V
)
REF
FB
t
I
I
Switch ON Time
38
50
µs
nA
nA
V
ON
FB
Feedback Pin Bias Current
Set Pin Bias Current
AO Output Low
LT1073, V = 0V
10
50
FB
V
= V
REF
60
120
0.4
SET
SET
V
I
= –100µA
AO
0.15
AO
Reference Line Regulation
1V ≤ V ≤ 1.5V
●
●
0.35
0.05
1.0
0.1
%V
%V
IN
1.5V ≤ V ≤ 12V
IN
V
Switch Saturation Voltage
Set-Up Mode
V
V
V
= 1.5V, I = 400mA
300
400
600
mV
mV
CESAT
IN
IN
IN
SW
●
●
= 1.5V, I = 500mA
400
550
750
mV
mV
SW
= 5V, I = 1A
700
1000
1500
mV
mV
SW
●
●
A
A2 Error Amp Gain
R = 100kΩ (Note 4)
400
1000
V/V
V
L
2
LT1073
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.5V unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
750
400
–0.3
1
MAX
UNITS
mA
I
I
Reverse Battery Current
Current Limit
(Note 5)
REV
LIM
220Ω Between I and V
mA
LIM
IN
Current Limit Temperature Coefficient
Switch OFF Leakage Current
Maximum Excursion Below GND
%/°C
µA
I
Measured at SW1 Pin
10
LEAK
V
I
≤ 10µA, Switch Off
SW1
–400
–350
mV
SW2
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 4: 100k resistor connected between a 5V source and the AO pin.
Note 5: The LT1073 is guaranteed to withstand continuous application of
Note 2: This specification guarantees that both the high and low trip point
of the comparator fall within the 202mV to 222mV range.
1.6V applied to the GND and SW2 pins while V , I and SW1 pins are
grounded.
IN LIM
Note 3: This specification guarantees that the output voltage of the fixed
versions will always fall within the specified range. The waveform at the
SENSE pin will exhibit a sawtooth shape due to the comparator hysteresis.
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch ON Voltage Step-Down Mode
(SW1 Pin Connected to VIN)
Saturation Voltage Step-Up Mode
(SW2 Pin Grounded)
Maximum Switch Current vs RLIM
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
1.2
1.0
0.8
0.6
0.4
0.2
0
1200
1100
1000
900
800
700
600
500
400
300
200
100
V
= 1.5V
L = 82µH
IN
V
= 3V
IN
V
= 1.25V
IN
V
= 1V
IN
V
= 5V
IN
V
= 1.5V
V
= 3V
IN
IN
V
= 2V
IN
0.1 0.2 0.3 0.4 0.5
(A)
0.7 0.8
0
0.6
0
0.4
0.6
0.8
1.0
1.2
0.2
10
100
(Ω)
1000
I
(A)
R
I
SWITCH
LIM
SWITCH
1073 G03
1073 G02
1073 G01
SET Pin Bias Current vs
Temperature
FB Pin Bias Current vs
Temperature
“Gain Block” Gain
1800
1600
1400
1200
1000
800
600
400
200
0
20
18
16
14
12
10
8
200
175
150
125
100
75
V
= 1.5V
= 100k
IN
L
R
50
6
25
4
0
–25
0
25
50
75
125
–50
100
–25
0
25
50
75
125
–50
100
–25
0
25
50
75
125
–50
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1073 G06
1073 G04
1073 G05
3
LT1073
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TYPICAL PERFOR A CE CHARACTERISTICS
Recommended Minimum
Inductance Value
Guaranteed Minimum Output
Current at 5V vs VIN
Supply Current vs Temperature
1000
100
10
300
250
200
150
100
50
150
140
130
120
110
100
90
V
= 1.5V
R
= 0V
IN
LIM
80
FOR V > 1.6V A
IN
70
68Ω RESISTOR
MUST BE CONNECTED
60
BETWEEN I
AND V
LIM
IN
0
50
1.0
3.0
4.0 4.5
1.0
1.5
2.0
2.5
3.0
3.5
1.5 2.0 2.5
3.5
5.0
–25
0
25
50
75
125
–50
100
INPUT VOLTAGE (V)
V
(V)
IN
TEMPERATURE (°C)
1073 G09
1073 G08
1073 G07
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PI FU CTIO S
ILIM (Pin 1): Connect this pin to VIN for normal use. Where
lower current limit is desired, connect a resistor between
ILIM and VIN. A 220Ω resistor will limit the switch current
to approximately 400mA.
GND (Pin 5): Ground.
AO (Pin 6): Auxiliary Gain Block (GB) Output. Open collec-
tor, can sink 100µA.
SET (Pin 7): GB Input. GB is an op amp with positive input
connected to SET pin and negative input connected to
212mV reference.
VIN (Pin 2): Input Supply Voltage
SW1 (Pin 3): Collector of Power Transistor. For step-up
mode connect to inductor/diode. For step-down mode
connect to VIN.
FB/SENSE (Pin 8): On the LT1073 (adjustable) this pin
goes to the comparator input. On the LT1073-5 and
LT1073-12, this pin goes to the internal application resis-
tor that sets output voltage.
SW2 (Pin 4): Emitter of Power Transistor. For step-up
mode connect to ground. For step-down mode connect to
inductor/diode. Thispinmustneverbeallowedtogomore
than a Schottky diode drop below ground.
W
LT1073-5 and LT1073-12
BLOCK DIAGRA S
SET
+
–
A2
A0
LT1073
SET
+
–
GAIN BLOCK/ERROR AMP
V
IN
A2
A0
I
SW1
LIM
212mV
REFERENCE
GAIN BLOCK/ERROR AMP
V
IN
A1
OSCILLATOR
Q1
I
SW1
Q1
LIM
212mV
DRIVER
SW2
REFERENCE
COMPARATOR
A1
OSCILLATOR
R2
940k
R1
GND
DRIVER
LT1073-5: R1 = 40k
LT1073-12: R2 = 16.3k
SENSE
SW2
COMPARATOR
1073 BD02
FB
1073 BD01
GND
4
LT1073
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OPERATIO
LT1073
The LT1073 is gated oscillator switcher. This type archi-
tecture has very low supply current because the switch is
cycledonlywhenthefeedbackpinvoltagedropsbelowthe
reference voltage. Circuit operation can best be under-
stood by referring to the LT1073 Block Diagram. Com-
parator A1 compares the FB pin voltage with the 212mV
referencesignal.WhenFBdropsbelow212mV,A1switches
on the 19kHz oscillator. The driver amplifier boosts the
signal level to drive the output NPN power switch Q1. An
adaptive base drive circuit senses switch current and
provides just enough base drive to ensure switch satura-
tion without overdriving the switch, resulting in higher
efficiency. The switch cycling action raises the output
voltage and FB pin voltage. When the FB voltage is suffi-
cient to trip A1, the oscillator is gated off. A small amount
of hysteresis built into A1 ensures loop stability without
external frequency compensation. When the comparator
is low the oscillator and all high current circuitry is turned
off, lowering device quiescent current to just 95µA for the
reference, A1 and A2.
A resistor connected between the ILIM pin and VIN adjusts
maximum switch current. When the switch current ex-
ceeds the set value, the switch is turned off. This feature
isespeciallyusefulwhensmallinductancevaluesareused
withhighinputvoltages.Iftheinternalcurrentlimitof1.5A
is desired, ILIM should be tied directly to VIN. Propagation
delay through the current-limit circuitry is about 2µs.
In step-up mode, SW2 is connected to ground and SW1
drives the inductor. In step-down mode, SW1 is con-
nected to VIN and SW2 drives the inductor. Output voltage
is set by the following equation in either step-up or step-
down modes where R1 is connected from FB to GND and
R2 is connected from VOUT to FB.
R2
R1
VOUT = 212mV
+ 1
(
)
LT1073-5 and LT1073-12
The LT1073-5 and LT1073-12 fixed output voltage ver-
sions have the gain-setting resistor on-chip. Only three
external components are required to construct a fixed-
output converter. 5µA flows through R1 and R2 in the
LT1073-5, and 12.3µA flows in the LT1073-12. This
current represents a load and the converter must cycle
from time to time to maintain the proper output voltage.
Output ripple, inherently present in gated-oscillator de-
signs, will typically run around 150mV for the LT1073-5
and 350mV for the LT1073-12 with the proper inductor/
capacitor selection. This output ripple can be reduced
considerablybyusingthegainblockampasapreamplifier
in front of the FB pin. See the Applications Information
section for details.
The oscillator is set internally for 38µs ON time and 15µs
OFF time, optimizing the device for step-up circuits where
V
OUT ≈ 3VIN, e.g., 1.5V to 5V. Other step-up ratios as well
as step-down (buck) converters are possible at slight
losses in maximum achievable power output.
A2 is a versatile gain block that can serve as a low-battery
detector, a linear post-regulator, or drive an undervoltage
lockout circuit. The negative input of A2 is internally
connected to the 212mV reference. An external resistor
divider from VIN to GND provides the trip point for A2. The
AO output can sink 100µA (use a 56k resistor pull-up to
5V). This line can signal a microcontroller that the battery
voltage has dropped below the preset level.
5
LT1073
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APPLICATIO S I FOR ATIO
Table 1. Component Selection for Step-Up Converters
INPUT
VOLTAGE (V)
BATTERY
TYPE
OUTPUT
VOLTAGE (V) CURRENT (MIN)
OUTPUT
INDUCTOR
VALUE (µH)
INDUCTOR
PART NUMBER
CAPACITOR
VALUE (µF)
NOTES
1.55-1.25
1.30-1.05
1.55-1.25
1.30-1.05
3.1-2.1
Single Alkaline
Single Ni-Cad
Single Alkaline
Single Ni-Cad
Two Alkaline
Two Alkaline
Lithium
3
3
60mA
20mA
30mA
10mA
80mA
25mA
100mA
25mA
5mA
82
G GA10-822K, CB 7300-12
G GA10-183K, CB 7300-16
G GA10-822K, CB 7300-12
G GA10-183K, CB 7300-16
G GA10-123K, CB 7300-14
G GA10-473K, CB 7300-21
G GA40-153K, CB 6860-15
G GA10-123K, CB 7300-14
G GA10-473K, CB 7300-21
G GA10-153K, CB 7300-15
G GA40-223K, CB 6860-17
G GA10-104K, CB 7300-25
G GA40-223K, CB 6860-17
150
47
180
5
82
100
22
5
180
5
120
470
150
470
220
100
220
470
100
150
*
*
*
3.1-2.1
5
470
3.3-2.5
5
150
3.1-2.1
Two Alkaline
Two Alkaline
Lithium
12
12
12
12
12
24
120
3.1-2.1
470
3.3-2.5
30mA
90mA
22mA
35mA
150
4.5-5.5
TTL Supply
TTL Supply
TTL Supply
220
*
*
*
4.5-5.5
1000
220
4.5-5.5
G = GOWANDA
CB = CADDELL-BURNS
*Add 68Ω from I to V
LIM IN
Measuring Input Current at Zero or Light Load
LT1073. The circuit must be “booted” by shorting V2 to
VSET. After the LT1073 output voltage has settled, discon-
nect the short. Input voltage is V2 and average input
current can be calculated by this formula:
Obtaining meaningful numbers for quiescent current and
efficiency at low output current involves understanding
howtheLT1073operates. Atveryloworzeroloadcurrent,
the device is idling for seconds at a time. When the output
voltage falls enough to trip the comparator, the power
switch comes on for a few cycles until the output voltage
rises sufficiently to overcome the comparator hysteresis.
When the power switch is on, inductor current builds up
to hundreds of milliamperes. Ordinary digital multimeters
are not capable of measuring average current because of
bandwidth and dynamic range limitations. A different
approach is required to measure the 100µA off-state and
500mA on-state currents of the circuit.
V2 – V1
100Ω
I =
IN
Inductor Selection
A DC/DC converter operates by storing energy as mag-
netic flux, in an inductor core and then switching this
energy into the load. Since it is flux, not charge, that is
stored, the output voltage can be higher, lower, or oppo-
site in polarity to the input voltage by choosing an appro-
priateswitchingtopology.Tooperateasanefficientenergy
transfer element, the inductor must fulfill three require-
ments. First, the inductance must be low enough for the
inductor to store adequate energy under the worst-case
condition of minimum input voltage and switch ON time.
The inductance must also be high enough so that maxi-
mum current ratings of the LT1073 and inductor are not
exceeded at the other worst-case condition of maximum
input voltage and ON time. Additionally, the inductor core
must be able to store the required flux, i.e., it must not
saturate. At power levels generally encountered with
LT1073-based designs, small axial-lead units with
1MΩ
12V
1µF*
–
100Ω
LT1073
LTC1050
CIRCUIT
V1
V2
+
+
1000µF
*NONPOLARIZED
V
SET
1073 F01
Figure 1. Test Circuit Measures No-Load
Quiescent Current of LT1073 Converter
Quiescent current can be accurately measured using the
circuit in Figure 1. VSET is set to the input voltage of the
6
LT1073
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APPLICATIO S I FOR ATIO
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1200
saturation current ratings in the 300mA to 1A range
(depending on application) are adequate. Lastly, the in-
ductor must have sufficiently low DC resistance so that
excessive power is not lost as heat in the windings. An
additional consideration is electro-magnetic interference
(EMI). Toroid and pot core type inductors are recom-
mended in applications where EMI must be kept to a
minimum; for example, where there are sensitive analog
circuitry or transducers nearby. Rod core types are a less
expensive choice where EMI is not a problem.
1000
800
600
400
200
0
0
1
2
3
4
5
V
(V)
IN
Specifying a proper inductor for an application requires
first establishing minimum and maximum input voltage,
output voltage and output current. In a step-up converter,
theinductiveeventsaddtotheinputvoltagetoproducethe
output voltage. Power required from the inductor is deter-
mined by:
1073 F02
Figure 2. Maximum Switch Current vs Input Voltage
Capacitor Selection
Selecting the right output capacitor is almost as important
as selecting the right inductor. A poor choice for a filter
capacitor can result in poor efficiency and/or high output
ripple.Ordinaryaluminumelectrolytics,whileinexpensive
andreadilyavailable, mayhaveunacceptablypoorequiva-
lent series resistance (ESR) and ESL (inductance). There
are low-ESR aluminum capacitors on the market specifi-
cally designed for switch-mode DC/DC converters which
work much better than general purpose units. Tantalum
capacitors provide still better performance at more ex-
pense. We recommend OS-CON capacitors from Sanyo
Corporation (San Diego, CA). These units are physically
quite small and have extremely low ESR. To illustrate,
Figures 3, 4, and 5 show the output voltage of an LT1073
based converter with three 100µF capacitors. The peak
switch current is 500mA in all cases. Figure 3 shows a
Sprague 501D aluminum capacitor. VOUT jumps by over
150mV when the switch turns off, followed by a drop in
voltage as the inductor dumps into the capacitor. This
worksouttobeanESRofover300mΩ.Figure4showsthe
same circuit, but with a Sprague 150D tantalum capacitor
replacing the aluminum unit. Output jump is now about
30mV, correspondingtoanESRof60mΩ. Figure5shows
the circuit with an OS-CON unit. ESR is now only 30mΩ.
PL = (VOUT + VD – VIN)(IOUT
)
where VD is the diode drop (0.5V for a 1N5818 Schottky).
Maximum power in the inductor is
PL= EL• fOSC
= L iPEAK2 • fOSC
1
2
where
VIN
R
–RtON
L
iPEAK
=
1– e
R = Switch equivalent resistance (1Ω maximum)
added to the DC resistance of the inductor and tON = ON
time of the switch.
AtmaximumVIN andONtime, iPEAK shouldnotbeallowed
to exceed the maximum switch current shown in Figure 2.
Some input/output voltage combinations will cause con-
tinuous1 mode operation. In these cases a resistor is
neededbetweenILIM (Pin1)andVIN (Pin 2)tokeepswitch
current under control. See the “Using the ILIM Pin” section
for details.
In very low power applications where every microampere
is important, leakage current of the capacitor must be
considered. The OS-CON units do have leakage current in
the 5µA to 10µA range. If the load is also in the
NOTE 1: i.e., inductor current does not go to zero when the switch is off.
7
LT1073
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APPLICATIO S I FOR ATIO
50mV/DIV
50mV/DIV
50mV/DIV
20µs/DIV
20µs/DIV
20µs/DIV
Figure 3. Aluminum
Figure 4. Tantalum
Figure 5. OS-CON
microampere range, a leaky capacitor will noticeably de-
crease efficiency. In this type application tantalum capaci-
torsarethebestchoice,withtypicalleakagecurrentsinthe
1µA to 5µA range.
short-circuit protected since there is a DC path from input
to output.
The usual step-up configuration for the LT1073 is shown
in Figure 6. The LT1073 first pulls SW1 low causing VIN-
VCESAT toappearacrossL1. AcurrentthenbuildsupinL1.
At the end of the switch ON time the current in L1 is2:
Diode Selection
Speed, forward drop and leakage current are the three
main considerations in selecting a catch diode for LT1073
converters. “General-purpose” rectifiers such as the
1N4001 are unsuitable for use in any switching regulator
application. Although they are rated at 1A, the switching
time of a 1N4001 is in the 10µs to 50µs range. At best,
efficiency will be severely compromised when these
diodes are used and at worst, the circuit may not work at
all. Most LT1073 circuits will be well served by a 1N5818
Schottky diode. The combination of 500mV forward drop
at 1A current, fast turn-on and turn-off time and 4µA to
10µA leakage current fit nicely with LT1073 requirements.
Atpeakswitchcurrentsof100mAorless, a1N4148signal
diode may be used. This diode has leakage current in the
1nA to 5nA range at 25°C and lower cost than a 1N5818.
(You can also use them to get your circuit up and running,
but beware of destroying the diode at 1A switch currents.)
InsituationswheretheloadisintermittentandtheLT1073
is idling most of the time, battery life can sometimes be
extended by using a silicon diode such as the 1N4933,
which can handle 1A but has leakage current of less than
1µA. Efficiency will decrease somewhat compared to a
1N5818 while delivering power, but the lower idle current
may be more important.
VIN
iPEAK
=
tON
L
NOTE 2: This simple expression neglects the effect of switch and coil resistance. These are taken
into account in the “Inductor Selection” section.
D1
L1
V
V
IN
OUT
R3*
I
V
IN
LIM
R2
R1
SW1
LT1073
+
C1
FB
GND
SW2
1073 F06
*= OPTIONAL
Figure 6. Step-Up Mode Hookup.
(Refer to Table 1 for Component Values)
Immediately after switch turn-off, the SW1 voltage pin
starts to rise because current cannot instantaneously stop
flowing in L1. When the voltage reaches VOUT + VD, the
inductor current flows through D1 into C1, increasing
VOUT. This action is repeated as needed by the LT1073 to
keep VFB at the internal reference voltage of 212mV. R1
and R2 set the output voltage according to the formula:
Step-Up (Boost Mode) Operation
A step-up DC/DC converter delivers an output voltage
higher than the input voltage. Step-up converters are not
8
LT1073
W U U
APPLICATIO S I FOR ATIO
U
R3 programs switch current limit. This is especially im-
portant in applications where the input varies over a wide
range. Without R3, the switch stays on for a fixed time
each cycle. Under certain conditions the current in L1 can
build up to excessive levels, exceeding the switch rating
and/or saturating the inductor. The 220Ω resistor pro-
grams the switch to turn off when the current reaches
approximately 400mA. When using the LT1073 in step-
down mode, output voltage should be limited to 6.2V or
less.
R2
R1
VOUT = 1+
212mV
(
)
Step-Down (Buck Mode) Operation
Astep-downDC/DCconverterconvertsahighervoltageto
a lower voltage. It is short-circuit protected because the
V
IN
R3
220Ω
I
V
SW1
FB
LIM IN
Inverting Configurations
LT1073
SW2
L1
+
The LT1073 can be configured as a positive-to-negative
converter (Figure 8), or a negative-to-positive converter
(Figure 9). In Figure 8, the arrangement is very similar to
a step-down, except that the high side of the feedback is
referredtoground.Thislevelshiftstheoutputnegative.As
in the step-down mode, D1 must be a Schottky diode, and
VOUT should be less than 6.2V.
V
C2
OUT
R2
GND
+
D1
1N5818
C1
R1
1073 FO7
Figure 7. Step-Down Mode Hookup
switch is in series with the output. Step-down converters
are characterized by low output voltage ripple but high
input current ripple. The usual hookup for an LT1073-
based step-down converter is shown in Figure 7.
+V
IN
+
C2 R3
I
V
SW1
FB
LIM IN
When the switch turns on, SW2 pulls up to VIN – VSW. This
LT1073
SW2
L1
puts a voltage across L1 equal to VIN – VSW – VOUT
,
causingacurrentto buildupinL1. Attheendoftheswitch
ON time, the current in L1 is equal to
GND
R1
R2
+
D1
C1
1N5818
V – VSW – VOUT
IN
iPEAK
=
tON
–V
OUT
L
1073 FO8
Figure 8. Positive-to-Negative Converter
When the switch turns off the SW2 pin falls rapidly and
actually goes below ground. D1 turns on when SW2
reaches 0.4V below ground. D1 MUST BE A SCHOTTKY
DIODE. The voltage at SW2 must never be allowed to go
below–0.5V.Asilicondiodesuchasthe1N4933willallow
SW2togoto–0.8V, causingpotentiallydestructivepower
dissipation inside the LT1073. Output voltage is deter-
mined by
D1
L1
+V
OUT
+
C1
R1
I
V
IN
LIM
SW1
LT1073
2N3906
+
C2
AO
FB
GND
SW2
R2
R2
R1
–V
IN
R1
VOUT = 1+
212mV
(
)
V
=
(R2)212mV + 0.6V
OUT
1073 F09
Figure 9. Negative-to-Positive Converter
9
LT1073
W U U
U
APPLICATIO S I FOR ATIO
In Figure 9, the input is negative while the output is
positive. In this configuration, the magnitude of the input
voltage can be higher or lower than the output voltage. A
levelshift, providedbythePNPtransistor, suppliesproper
polarity feedback information to the regulator.
VOUT + VDIODE
1
<
V – VSW
IN
1– DC
When the input and output voltages satisfy this relation-
ship, inductor current does not go to zero during the
switch OFF time. When the switch turns on again, the
current ramp starts from the nonzero current level in the
inductor just prior to switch turn-on. As shown in
Figure 10, the inductor current increases to a high level
before the comparator turns off the oscillator. This high
current can cause excessive output ripple and requires
oversizingtheoutputcapacitorandinductor. WiththeILIM
feature, however, the switch current turns off at a pro-
grammed level as shown in Figure 11, keeping output
ripple to a minimum.
Using the ILIM Pin
The LT1073 switch can be programmed to turn off at a set
switch current, a feature not found on competing devices.
This enables the input to vary over a wide range without
exceeding the maximum switch rating or saturating the
inductor. Consider the case where analysis shows the
LT1073 must operate at an 800mA peak switch current
with a 2V input. If VIN rises to 4V, the peak switch current
will rise to 1.6A, exceeding the maximum switch current
rating.Withtheproperresistor(seethe“MaximumSwitch
Current vs RLIM” characteristic) selected, the switch cur-
rent will be limited to 800mA, even if the input voltage
increases. The LT1073 does this by sampling a small
fraction of the switch current and passing this current
throughtheexternalresistor. WhenthevoltageontheILIM
pin drops a VBE below VIN, the oscillator terminates the
cycle. Propagation delay through this loop is about 2µs.
Using the Gain Block
The gain block (GB) on the LT1073 can be used as an error
amplifier, low-battery detector or linear post-regulator.
ThegainblockitselfisaverysimplePNPinputopampwith
an open-collector NPN output. The (–) input of the gain
block is tied internally to the 212mV reference. The (+)
input comes out on the SET pin.
Another situation where the ILIM feature is useful is when
the device goes into continuous mode operation. This
occurs in step-up mode when
Arrangement of the gain block as a low battery detector is
straightforward.Figure12showshookup.R1andR2need
only be low enough in value so that the bias current of the
SET input does not cause large errors. 100kΩ for R2 is
adequate.
Output ripple of the LT1073, normally 150mV at 5VOUT
,
PROGRAMMED CURRENT LIMIT
can be reduced significantly by placing the gain block in
front of the FB input as shown in Figure 13. This effectively
I
L
I
L
reduces the comparator hysteresis by the gain of the gain
ON
ON
block. Output ripple can be reduced to just a few millivolts
SWITCH
OFF
SWITCH
OFF
using this technique. Ripple reduction wo
1
r
07
ks with step-
3 F1
1
1073 F10
down or inverting modes as well.
Figure 11. Current Limit Keeps Inductor Current Under Control
Figure 10. No Current Limit Causes
Large Inductor Current Build-Up
10
LT1073
W U U
U
APPLICATIO S I FOR ATIO
D1
L1
V
OUT
5V
R3
V
IN
LT1073
680k
I
V
LIM
IN
SW1
LT1073
R2
100k
212mV
REF
–
+
AO
R1
R2
+
V
A0
BAT
TO
C1
PROCESSOR
SET
FB
SET
V
=
BAT
GND
SW2
R1
GND
V
LB
)
212mV
R1 = R2
(
–1
1073 F13
R2
V
= BATTERY TRIP POINT
V
OUT
+ 1 212mV
LB
(
)
R1
)
(
1073 F12
Figure 12. Settling Low Battery Detector Trip Point
Table 2. Inductor Manufacturers
Figure 13. Output Ripple Reduction Using Gain Block
Table 3. Capacitor Manufacturers
MANUFACTURER
PART NUMBERS
MANUFACTURER
PART NUMBERS
Gowanda Electronics Corporation
1 Industrial Place
Gowanda, NY 14070
GA10 Series
GA40 Series
Sanyo Video Components
1201 Sanyo Avenue
San Diego, CA 92073
619-661-6322
OS-CON Series
716-532-2234
Caddell-Burns
7300 Series
6860 Series
Nichicon America Corporation
927 East State Parkway
Schaumberg, IL 60173
708-843-7500
PL Series
258 East Second Street
Mineola, NY 11501
516-746-2310
Coiltronics International
984 S.W. 13th Court
Pompano Beach, FL 33069
305-781-8900
Custom Toroids
Surface Mount
Sprague Electric Company
Lower Main Street
Stanford, ME 04073
207-324-4140
150D Solid Tantalums
550D Tantalex
Toko America Incorporated
1250 Feehanville Drive
Mount Prospect, IL 60056
312-297-0070
Type 8RBS
Renco Electronics Incorporated
60 Jefryn Boulevard, East
Deer Park, NY 11729
800-645-5828
RL1283
RL1284
U
TYPICAL APPLICATIO S
1.5V to 3V Step-Up Converter
1.5V to 9V Step-Up Converter
L1†
L1†
1N5818
1N5818
120µH
9V OUTPUT
7mA AT V
120µH
3V OUTPUT
20mA AT
BATTERY
= 1V
BATTERY
BATTERY
16mA AT V
= 1.5V
V
= 1V
220Ω
I
V
LIM
IN
SW1
LT1073
I
V
IN
LIM
1M*
536k*
+
SW1
LT1073
+
1.5V
CELL
1.5V
CELL
47µF
100µF
FB
FB
GND
SW2
GND
SW2
24.3k*
40.2k*
* 1% METAL FILM
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
* 1% METAL FILM
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
†
1073 TA04
†
1073 TA03
11
LT1073
U
TYPICAL APPLICATIO S
1.5V to 12V Step-Up Converter
3V to 5V Step-Up Converter
L1†
68µH
L1†
120µH
1N5818
1N5818
5V OUTPUT
100mA AT
12V OUTPUT
5mA AT V
= 1V
= 1.5V
BATTERY
V
= 2V
BATTERY
16mA AT V
BATTERY
100Ω
I
V
IN
LIM
I
V
LIM
IN
SW1
LT1073-12
SW1
LT1073-5
+
+
TWO
1.5V
CELLS
1.5V
CELL
100µF
47µF
SENSE
SW2
SENSE
SW2
GND
GND
†
†
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
1073 TA06
1073 TA05
3V to 12V Step-Up Converter
3V to 15V Step-Up Converter
L1†
68µH
L1†
68µH
1N5818
1N5818
12V OUTPUT
35mA AT
BATTERY
15V OUTPUT
27mA AT
V
= 2V
V
= 2V
BATTERY
100Ω
100Ω
1M*
I
V
IN
I
V
IN
LIM
LIM
SW1
SW1
+
+
TWO
1.5V
CELLS
TWO
1.5V
CELLS
47µF
47µF
LT1073-12
LT1073
SENSE
SW2
FB
GND
GND
SW2
14.3k*
†
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
* 1% METAL FILM
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
1073 TA07
†
1073 TA08
5V to 12V Step-Up Converter
5V to 15V Step-Up Converter
L1†
150µH
L1†
150µH
1N5818
1N5818
12V OUTPUT
130mA AT 4.5V
15V OUTPUT
100mA AT 4.5V
5V
IN
5V
IN
IN
IN
50Ω
50Ω
I
V
1M*
LIM
IN
SW1
LT1073-12
I
V
IN
LIM
+
+
100µF
100µF
SW1
LT1073
+
+
100µF
100µF
SENSE
SW2
GND
FB
GND
SW2
14.3k*
†
L1 = GOWANDA GA20-153k
OR CADDELL-BURNS 7200-15
1073 TA09
* 1% METAL FILM
1073 TA10
† L1 = GOWANDA GA20-153k
OR CADDELL-BURNS 7200-15
12
LT1073
U
TYPICAL APPLICATIO S
1.5V to 5V Step-Up Converter with Low-Battery Detector
1.5V to 5V Step-Up Converter with Logic Shutdown
L1†
82µH
L1†
82µH
1N5818
1N5818
5V OUTPUT
5V OUTPUT
100k
909k*
442k*
100k*
I
V
IN
I
V
IN
LIM
LIM
1.5V
CELL
SW1
LT1073
SET
SW1
+
+
1.5V
CELL
100µF
100µF
LT1073-5
FB
AO
SENSE
SW2
GND
SW2
GND
LO BAT
1N4148
74C04
40.2k*
GOES LOW
AT V
BATTERY
= 1.15V
* 1% METAL FILM
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
†
1073 TA11
1073 TA12
SHUTDOWN
* 1% METAL FILM
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
OPERATE
†
9V to 5V Step-Down Converter
9V to 3V Step-Down Converter
3V OUTPUT
536k*
220Ω
220Ω
I
V
I
V
LIM
IN
SW1
LT1073-5
LIM
IN
SW1
LT1073
9V
BATTERY
9V
BATTERY
5V OUTPUT
SENSE
SW2
FB
L1†
100µH
L1†
100µH
GND
GND
SW2
40.2k*
+
+
1N5818
100µF
1N5818
100µF
†
L1 = GOWANDA GA10-103k
OR CADDELL-BURNS 7300-13
* 1% METAL FILM
L1 = GOWANDA GA10-103k
OR CADDELL-BURNS 7300-13
1073 TA14
†
1073 TA13
Memory Backup Supply
1.5V to 5V Bootstrapped Step-Up Converter
5V TO MEMORY,
4.5V WHEN MAIN
SUPPLY OPEN
L1†
47µH
5V MAIN
SUPPLY
1N5818
5V OUTPUT
50mA
L1†
82µH
1N5818
2N3906
56Ω
2.2k
I
V
IN
LIM
+
806k*
I
V
IN
1.5V
CELL
LIM
100µF
SW1
LT1073
+
SW1
LT1073-5
1.5V
CELL
100µF**
FB
SENSE
SW2
GND
SW2
GND
40.2k*
* 1% METAL FILM
†
1073 TA16
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
**OPTIONAL
1073 TA15
†
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
MINIMUM START-UP VOLTAGE = 1.1V
13
LT1073
U
TYPICAL APPLICATIO S
1.5V to 5V Low Noise Step-Up Converter
3V to 5V Step-Up Converter with Undervoltage Lockout
L1†
68µH
L1†
5V OUTPUT
100mA
1N5818
82µH
1N5818
5V OUTPUT
LOCKOUT
AT 1.8V
20mV RIPPLE
P-P
100k
100Ω
680k
1.5V
909k*
I
V
I
V
IN
LIM
IN
LIM
909k*
1M*
100k
2.2M
AO
SW1
LT1073
SW1
LT1073
FB
2N3906
+
+
100µF
OS-CON
100µF
3V
SET
FB
AO
SET
GND
SW2
GND
SW2
100k*
40.3k*
40.2k*
* 1% METAL FILM
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
* 1% METAL FILM
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
†
†
1073 TA17
1073 TA18
1.5V to 5V Very Low Noise Step-Up Converter
9V to 5V Reduced Noise Step-Down Converter
L1†
L1†
1N5818
470µH
47µH
+V
5V
OUT
IN
6.5V TO 12V
5V OUTPUT
BATTERY
10mV RIPPLE
P-P
90mA AT 6.5V
IN
5mA AT V
= 1V
680k
220Ω
680k
1.5V
909k*
1N5818
I
V
SW1
LIM IN
I
V
IN
LIM
+
909k*
100µF
OS-CON
FB
SW1
LT1073
FB
+
100µF
OS-CON
LT1073
AO
GND
SET
AO
SET
SW2
GND
SW2
40.2k*
40.2k*
1073 TA20
* 1% METAL FILM
* 1% METAL FILM
L1 = GOWANDA GA10-472k
OR CADDELL-BURNS 7300-09
EFFICIENCY ≈ 80%
I ≈ 130µA
Q
OUTPUT NOISE ≈ 100mV
P-P
†
†
L1 = GOWANDA GA10-473k
OR CADDELL-BURNS 7300-21
EFFICIENCY = 83% AT 5mA LOAD
1073 TA19
3V to 6V at 1A Step-Up Converter
1.5V Powered 350ps Risetime Pulse Generator
INPUT
3V TO 6V
(2 LITHIUM CELLS)
6V OUTPUT
1A AT
IN
L1†
25µH
MUR120
90V BIAS
V
= 3V
L1†
150µH
0.1µF
0.1µF
1.5V
MUR120
1M
I
V
IN
560k
549k*
LIM
1N5820
C1
SW1
LT1073
FB
2pF TO 4pF
220Ω
10M
+
+
2200µF
1000µF
I
V
IN
LIM
MUR120
0.1µF
AO
SET
Q1
SW1
LT1073
2N2369
GND
SW2
OUTPUT
5V INTO
50Ω PULSE
WIDTH ≈ 1ns
1N5818
FB
51Ω
20k*
MTP3055EL
GND
SW2
24k 10k
50Ω
2N3906
†L1 = TOKO 262LYF-0095K
SELECT Q1 AND C1 FOR OPTIMUM RISE AND FALL
1073 TA22
5.1k
* 1% METAL FILM
†
L1 = COILTRONICS CTX25-5-52
1073 TA21
LOW I (<250µA)
Q
14
LT1073
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400*
(10.160)
MAX
0.130 ± 0.005
0.300 – 0.325
0.045 – 0.065
(3.302 ± 0.127)
(1.143 – 1.651)
(7.620 – 8.255)
8
1
7
6
5
0.065
(1.651)
TYP
0.255 ± 0.015*
(6.477 ± 0.381)
0.009 – 0.015
(0.229 – 0.381)
0.125
0.020
(0.508)
MIN
(3.175)
MIN
+0.035
–0.015
2
4
3
0.325
0.018 ± 0.003
0.100
(2.54)
BSC
+0.889
8.255
(0.457 ± 0.076)
(
)
N8 1098
–0.381
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
(0.254 – 0.508)
7
5
8
6
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
0.016 – 0.050
(0.406 – 1.270)
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
TYP
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
SO8 1298
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
3
4
2
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.
15
LT1073
U
TYPICAL APPLICATIO S
1.5V Powered Temperature Compensated Crystal Oscillator
L1†
820µH
1.5V
30.1k* 27.4k*
150k*
+
–
I
V
LIM
IN
SW1
LT1073
SET
FB
LT1017
150k
1.5V
2N3906
1k
6.81K*
LM134-3
1.5V
2N3906
100k
A0
SW2
1N4148
1.5V
150k*
73.2k*
+
+
39.2k*
47µF
47µF
100Ω
100k
10M*
2N3904
OUTPUT
1MHz
0.05ppm/°C
100k
1MHz
560k
510pF
510pF
0.02µF
MV209
* 1% METAL FILM
2k
†
L1 = J.W. MILLER #100267
= AT CUT –35° 20' ANGLE
1073 TA23
1.5V Powered α, β, γParticle Detector
0.01µF
T1
3
10
1N976
D1
D2
D3
1M
3M
330Ω
4
1N4148
NC
I
V
2N3906
LIM
IN
SW1
LT1073
X1
0.01µF
5
7
FB
2N3904
NC
NC
1
2
0.01µF
1M
1.5V
10k
AO
SET
500V
REGULATED
GND
SW2
10M
68pF
600V
1N5818
T1 = COILTRONICS CTX10052-1
X1 = PROJECTS UNLIMITED AT-
11k OR 8Ω SPEAKER
1073 TA24
R1
500M
210k
0.01µF
U1
D1, D2, D3 = MUR1100
R1 = VICTOREEN MOX-300
U1 = LND-712 CORP., OCEANSIDE, NY
RELATED PARTS
PART NUMBER
LT1307
DESCRIPTION
COMMENTS
Single Cell Micropower 600kHz PWM DC/DC Converter
3.3V at 75mA from One Cell, MSOP Package
LT1316
Burst ModeTM Operation DC/DC with Programmable Current Limit
2-Cell Micropower DC/DC with Low-Battery Detector
Single Cell Micropower DC/DC Converter
1.5V Minimum, Precise Control of Peak Current Limit
3.3V at 200mA from Two Cells, 600kHz Fixed Frequency
3V at 30mA from 1V, 1.7MHz Fixed Frequency
–5V at 150mA from 5V Input, Tiny SOT-23 Package
5V at 200mA from 3.3V Input, Tiny SOT-23 Package
20V at 12mA from 2.5V, Tiny SOT-23 Package
–15V at 12mA from 2.5V, Tiny SOT-23 Package
5V at 450mA from 3.3V Input, Tiny SOT-23 Package
LT1317
LT1610
LT1611
Inverting 1.4MHz Switching Regulator in 5-Lead SOT-23
1.4MHz Switching Regulator in 5-Lead SOT-23
LT1613
LT1615
Micropower Constant Off-Time DC/DC Converter in 5-Lead SOT-23
Micropower Inverting DC/DC Converter in 5-Lead SOT-23
LT1617
LT1930/LT1930A 1.2MHz/2.2MHz, 1A Switching Regulator in 5-Lead SOT-23
LT1931/LT1931A 1.2MHz/2.2MHz, 1A Inverting Switching Regulator in 5-Lead SOT-23 –5V at 350mA from 5V Input, Tiny SOT-23 Package
Burst Mode operation is a trademark of Linear Technology Corporation.
1073fa LT/TP 0301 2K REV A • PRINTED IN USA
16 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
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LINEAR TECHNOLOGY CORPORATION 2000
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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