LINER LT1073CS8-12 Micropower dc/dc converter adjustable and fixed 5v, 12v Datasheet

LT1073
Micropower
DC/DC Converter
Adjustable and Fixed 5V, 12V
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FEATURES
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DESCRIPTIO
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
Fixed or Adjustable Output Voltage Versions
Space-Saving 8-Pin PDIP or SO-8 Package
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APPLICATIO S
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Pagers
Cameras
Single-Cell to 5V Converters
Battery Backup Supplies
Laptop and Palmtop Computers
Cellular Telephones
Portable Instruments
4mA to 20mA Loop Powered Instruments
Hand-Held Inventory Computers
Battery-Powered α, β, and γ Particle Detectors
Average current drain of the LT1073-5 used as shown in
the Typical Application circuit below is just 135µA unloaded, 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.
The device can easily be configured as a step-up or stepdown converter, although for most step-down applications or input sources greater than 3V, the LT1173 is
recommended. Switch current limiting is user-adjustable
by adding a single external resistor. Unique reversebattery protection circuitry limits reverse current to safe,
nondestructive levels at reverse supply voltages up to
1.6V.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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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 lowbattery detector or linear post-regulator.
TYPICAL APPLICATION
Single Alkaline “AA” Cell Operating
Hours vs DC Load Current
Single-Cell to 5V Converter
1
ILIM
1.5V
AA CELL*
1000
5V
40mA
2
VIN
SW1
3
LT1073-5
SENSE
GND
5
SW2
4
8
+
100µF
SANYO
0S-CON
CONTINUOUS OPERATION (HOURS)
CADDELL-BURNS
7300-12
1N5818
82µH
100
L = 180µH
10
L = 82µH
1
OPERATES WITH CELL VOLTAGE ≥1V
*ADD 10µF DECOUPLING CAPACITOR IF
BATTERY IS MORE THAN 2" AWAY FROM LT1073
1
1073 TA01
10
LOAD CURRENT (mA)
100
LT1073 TA02
1
LT1073
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
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
ILIM 1
8
FB (SENSE)*
VIN 2
7
SET
SW1 3
6
A0
SW2 4
5
GND
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
*FIXED VERSIONS
TJMAX = 125°C, θJA = 100°C/W (N8)
TJMAX = 125°C, θJA = 120°C/W (S8)
ORDER PART
NUMBER
LT1073CN8
LT1073CN8-5
LT1073CN8-12
LT1073CS8
LT1073CS8-5
LT1073CS8-12
S8 PART MARKING
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
IQ
Quiescent Current
Switch Off
IQ
Quiescent Current, Step-Up
Mode Configuration
No Load
VIN
Input Voltage
Step-Up Mode
●
Step-Down Mode
●
Comparator Trip Point Voltage
LT1073 (Note 2)
●
202
Output Sense Voltage
LT1073-5 (Note 3)
LT1073-12 (Note 3)
●
●
4.75
11.4
Comparator Hysteresis
LT1073
●
5
10
mV
Output Hysteresis
LT1073-5
LT1073-12
●
●
125
300
250
600
mV
mV
VOUT
MIN
●
LT1073-5
LT1073-12
TYP
MAX
UNITS
95
130
µA
µA
µA
135
250
1.15
1.0
12.6
12.6
V
V
30
V
212
222
mV
5
12
5.25
12.6
V
V
fOSC
Oscillator Frequency
DC
Duty Cycle
tON
Switch ON Time
IFB
Feedback Pin Bias Current
LT1073, VFB = 0V
●
10
50
nA
ISET
Set Pin Bias Current
VSET = VREF
●
60
120
nA
VAO
AO Output Low
IAO = –100µA
●
0.15
0.4
V
Reference Line Regulation
1V ≤ VIN ≤ 1.5V
1.5V ≤ VIN ≤ 12V
●
●
0.35
0.05
1.0
0.1
%V
%V
Switch Saturation Voltage
Set-Up Mode
VIN = 1.5V, ISW = 400mA
300
400
600
mV
mV
400
550
750
mV
mV
700
1000
1500
mV
mV
VCESAT
Full Load (VFB = VREF)
●
15
19
23
kHz
●
65
72
80
%
●
30
38
50
µs
●
VIN = 1.5V, ISW = 500mA
●
VIN = 5V, ISW = 1A
●
AV
2
A2 Error Amp Gain
RL = 100kΩ (Note 4)
●
400
1000
V/V
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
IREV
Reverse Battery Current
(Note 5)
750
mA
ILIM
Current Limit
220Ω Between ILIM and VIN
400
mA
Current Limit Temperature Coefficient
MAX
UNITS
–0.3
ILEAK
Switch OFF Leakage Current
Measured at SW1 Pin
VSW2
Maximum Excursion Below GND
ISW1 ≤ 10µA, Switch Off
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: This specification guarantees that both the high and low trip point
of the comparator fall within the 202mV to 222mV range.
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.
%/°C
1
10
µA
–400
–350
mV
Note 4: 100k resistor connected between a 5V source and the AO pin.
Note 5: The LT1073 is guaranteed to withstand continuous application of
1.6V applied to the GND and SW2 pins while VIN, ILIM and SW1 pins are
grounded.
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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
1.2
1200
VIN = 1.5V
VIN = 1.25V
VCESAT (V)
0.8
VIN = 1V
VIN = 5V
0.6
VIN = 3V
0.4
VIN = 2V
1.2
1.1
1.0
0.9
0.2
0.8
0
0.7
VIN = 3V
1000
SWITCH CURRENT (mA)
SWITCH ON VOLTAGE (V)
1.0
L = 82µH
1100
1.3
900
800
700
600
VIN = 1.5V
500
400
300
200
0
0.2
0.4
0.6
0.8
1.0
0
1.2
0.1
0.3
0.2
ISWITCH (A)
0.4
0.5
0.6
100
10
0.8
1073 G03
SET Pin Bias Current vs
Temperature
“Gain Block” Gain
200
1800
18
175
1600
14
12
10
8
6
125
100
75
25
50
75
100
125
TEMPERATURE (°C)
800
200
0
25
50
75
100
125
0
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
TEMPERATURE (°C)
1073 G04
1000
400
25
0
1200
600
50
0
–50 –25
VIN = 1.5V
RL = 100k
1400
150
GB GAIN (V/V)
SET PIN BIAS CURRENT (nA)
20
16
1000
1073 G02
FB Pin Bias Current vs
Temperature
4
–50 –25
100
RLIM (Ω)
ISWITCH (A)
1073 G01
FB BIAS CURRENT (nA)
0.7
1073 G05
1073 G06
3
LT1073
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TYPICAL PERFOR A CE CHARACTERISTICS
Recommended Minimum
Inductance Value
Supply Current vs Temperature
SUPPLY CURRENT (µA)
130
120
110
100
90
80
70
1000
RLIM = 0V
250
OUTPUT CURRENT (mA)
140
300
VIN = 1.5V
MINIMUM INDUCTANCE (µH)
150
Guaranteed Minimum Output
Current at 5V vs VIN
200
150
100
100
FOR VIN > 1.6V A
68Ω RESISTOR
MUST BE CONNECTED
BETWEEN ILIM AND VIN
50
60
50
–50 –25
25
0
50
75
100
125
0
1.0 1.5
TEMPERATURE (°C)
2.0
2.5 3.0 3.5 4.0
INPUT VOLTAGE (V)
4.5
10
1.0
5.0
1.5
2.0
2.5
VIN (V)
3.5
1073 G09
1073 G08
1073 G07
3.0
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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.
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.
SW2 (Pin 4): Emitter of Power Transistor. For step-up
mode connect to ground. For step-down mode connect to
inductor/diode. This pin must never be allowed to go more
than a Schottky diode drop below ground.
GND (Pin 5): Ground.
AO (Pin 6): Auxiliary Gain Block (GB) Output. Open collector, 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.
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 resistor that sets output voltage.
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LT1073-5 and LT1073-12
BLOCK DIAGRA S
SET
+
LT1073
A2
+
SET
A0
–
A2
GAIN BLOCK/ERROR AMP
VIN
A0
–
ILIM
VIN
A1
ILIM
OSCILLATOR
Q1
SW1
DRIVER
212mV
REFERENCE
SW2
COMPARATOR
A1
GND
OSCILLATOR
Q1
R1
DRIVER
COMPARATOR
FB
4
SW1
212mV
REFERENCE
GAIN BLOCK/ERROR AMP
SENSE
SW2
1073 BD01
R2
940k
GND
LT1073-5: R1 = 40k
LT1073-12: R2 = 16.3k
1073 BD02
LT1073
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OPERATIO
LT1073
The LT1073 is gated oscillator switcher. This type architecture has very low supply current because the switch is
cycled only when the feedback pin voltage drops below the
reference voltage. Circuit operation can best be understood by referring to the LT1073 Block Diagram. Comparator A1 compares the FB pin voltage with the 212mV
reference signal. When FB drops below 212mV, A1 switches
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 saturation 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 sufficient 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.
The oscillator is set internally for 38µs ON time and 15µs
OFF time, optimizing the device for step-up circuits where
VOUT ≈ 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.
A resistor connected between the ILIM pin and VIN adjusts
maximum switch current. When the switch current exceeds the set value, the switch is turned off. This feature
is especially useful when small inductance values are used
with high input voltages. If the internal current limit of 1.5A
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 connected to VIN and SW2 drives the inductor. Output voltage
is set by the following equation in either step-up or stepdown modes where R1 is connected from FB to GND and
R2 is connected from VOUT to FB.
 R2 
VOUT = 212mV  + 1
 R1 
(
)
LT1073-5 and LT1073-12
The LT1073-5 and LT1073-12 fixed output voltage versions have the gain-setting resistor on-chip. Only three
external components are required to construct a fixedoutput 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 designs, 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
considerably by using the gain block amp as a preamplifier
in front of the FB pin. See the Applications Information
section for details.
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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)
OUTPUT
CURRENT (MIN)
INDUCTOR
VALUE (µH)
INDUCTOR
PART NUMBER
CAPACITOR
VALUE (µF)
1.55-1.25
Single Alkaline
3
60mA
82
G GA10-822K, CB 7300-12
150
1.30-1.05
Single Ni-Cad
3
20mA
180
G GA10-183K, CB 7300-16
47
1.55-1.25
Single Alkaline
5
30mA
82
G GA10-822K, CB 7300-12
100
1.30-1.05
Single Ni-Cad
5
10mA
180
G GA10-183K, CB 7300-16
22
3.1-2.1
Two Alkaline
5
80mA
120
G GA10-123K, CB 7300-14
470
*
3.1-2.1
Two Alkaline
5
25mA
470
G GA10-473K, CB 7300-21
150
*
3.3-2.5
Lithium
5
100mA
150
G GA40-153K, CB 6860-15
470
*
3.1-2.1
Two Alkaline
12
25mA
120
G GA10-123K, CB 7300-14
220
3.1-2.1
Two Alkaline
12
5mA
470
G GA10-473K, CB 7300-21
100
3.3-2.5
Lithium
12
30mA
150
G GA10-153K, CB 7300-15
220
4.5-5.5
TTL Supply
12
90mA
220
G GA40-223K, CB 6860-17
470
*
4.5-5.5
TTL Supply
12
22mA
1000
G GA10-104K, CB 7300-25
100
*
4.5-5.5
TTL Supply
24
35mA
220
G GA40-223K, CB 6860-17
150
*
G = GOWANDA
CB = CADDELL-BURNS
Measuring Input Current at Zero or Light Load
Obtaining meaningful numbers for quiescent current and
efficiency at low output current involves understanding
how the LT1073 operates. At very low or zero load current,
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.
1MΩ
12V
1µF*
–
100Ω
LTC1050
+
V1
V2
LT1073
CIRCUIT
+
1000µF
VSET
*NONPOLARIZED
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
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NOTES
*Add 68Ω from ILIM to VIN
LT1073. The circuit must be “booted” by shorting V2 to
VSET. After the LT1073 output voltage has settled, disconnect the short. Input voltage is V2 and average input
current can be calculated by this formula:
IIN =
V2 – V1
100Ω
Inductor Selection
A DC/DC converter operates by storing energy as magnetic 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 opposite in polarity to the input voltage by choosing an appropriate switching topology. To operate as an efficient energy
transfer element, the inductor must fulfill three requirements. 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 maximum 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
LT1073
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APPLICATIO S I FOR ATIO
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,
the inductive events add to the input voltage to produce the
output voltage. Power required from the inductor is determined by:
PL = (VOUT + VD – VIN)(IOUT)
where VD is the diode drop (0.5V for a 1N5818 Schottky).
Maximum power in the inductor is
P L = E L• fOSC
2
1
= L iPEAK • fOSC
2
where
V 
iPEAK =  IN 
 R 

–RtON 
1–
e

L 

R = Switch equivalent resistance (1Ω maximum)
added to the DC resistance of the inductor and t ON = ON
time of the switch.
At maximum VIN and ON time, iPEAK should not be allowed
to exceed the maximum switch current shown in Figure 2.
Some input/output voltage combinations will cause continuous1 mode operation. In these cases a resistor is
needed between ILIM (Pin 1) and VIN (Pin 2) to keep switch
current under control. See the “Using the ILIM Pin” section
for details.
NOTE 1: i.e., inductor current does not go to zero when the switch is off.
1200
1000
ISWITCH (mA)
saturation current ratings in the 300mA to 1A range
(depending on application) are adequate. Lastly, the inductor 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 recommended 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.
800
600
400
200
0
0
1
2
3
4
5
VIN (V)
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. Ordinary aluminum electrolytics, while inexpensive
and readily available, may have unacceptably poor equivalent series resistance (ESR) and ESL (inductance). There
are low-ESR aluminum capacitors on the market specifically designed for switch-mode DC/DC converters which
work much better than general purpose units. Tantalum
capacitors provide still better performance at more expense. 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
works out to be an ESR of over 300mΩ. Figure 4 shows the
same circuit, but with a Sprague 150D tantalum capacitor
replacing the aluminum unit. Output jump is now about
30mV, corresponding to an ESR of 60mΩ. Figure 5 shows
the circuit with an OS-CON unit. ESR is now only 30mΩ.
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
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LT1073
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APPLICATIO S I FOR ATIO
50mV/DIV
50mV/DIV
50mV/DIV
20µs/DIV
20µs/DIV
Figure 3. Aluminum
Figure 4. Tantalum
microampere range, a leaky capacitor will noticeably decrease efficiency. In this type application tantalum capacitors are the best choice, with typical leakage currents in the
1µA to 5µA range.
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.
At peak switch currents of 100mA or less, a 1N4148 signal
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.)
In situations where the load is intermittent and the LT1073
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.
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
20µs/DIV
Figure 5. OS-CON
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 VINVCESAT to appear across L1. A current then builds up in L1.
At the end of the switch ON time the current in L1 is2:
iPEAK =
V IN
t ON
L
NOTE 2: This simple expression neglects the effect of switch and coil resistance. These are taken
into account in the “Inductor Selection” section.
L1
D1
VIN
VOUT
R3*
ILIM
VIN
R2
+
SW1
C1
LT1073
FB
GND
SW2
R1
*= OPTIONAL
1073 F06
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:
LT1073
U
W
U U
APPLICATIO S I FOR ATIO
VOUT
 R2
=  1 +  212mV
 R1
(
)
Step-Down (Buck Mode) Operation
A step-down DC/DC converter converts a higher voltage to
a lower voltage. It is short-circuit protected because the
VIN
R3
220Ω
R3 programs switch current limit. This is especially important 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 programs the switch to turn off when the current reaches
approximately 400mA. When using the LT1073 in stepdown mode, output voltage should be limited to 6.2V or
less.
ILIM VIN SW1
Inverting Configurations
FB
+
LT1073
L1
SW2
C2
VOUT
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 LT1073based step-down converter is shown in Figure 7.
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
referred to ground. This level shifts the output negative. As
in the step-down mode, D1 must be a Schottky diode, and
VOUT should be less than 6.2V.
+VIN
+
C2 R3
ILIM VIN SW1
FB
When the switch turns on, SW2 pulls up to VIN – VSW. This
puts a voltage across L1 equal to VIN – VSW – VOUT,
causing a current to build up in L1. At the end of the switch
ON time, the current in L1 is equal to
iPEAK
LT1073
GND
VOUT
(
)
+
R2
C1
–VOUT
1073 FO8
Figure 8. Positive-to-Negative Converter
L1
D1
+VOUT
+
C1
ILIM
+
C2
R1
VIN
SW1
2N3906
LT1073
AO
GND
 R2
=  1 +  212mV
 R1
R1
D1
1N5818
V –V –V
= IN SW OUT tON
L
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. A silicon diode such as the 1N4933 will allow
SW2 to go to –0.8V, causing potentially destructive power
dissipation inside the LT1073. Output voltage is determined by
L1
SW2
FB
SW2
R2
–VIN
VOUT =
( R1
)212mV + 0.6V
R2
1073 F09
Figure 9. Negative-to-Positive Converter
9
LT1073
U
W
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
level shift, provided by the PNP transistor, supplies proper
polarity feedback information to the regulator.
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. With the proper resistor (see the “Maximum Switch
Current vs RLIM” characteristic) selected, the switch current 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
through the external resistor. When the voltage on the ILIM
pin drops a VBE below VIN, the oscillator terminates the
cycle. Propagation delay through this loop is about 2µs.
Another situation where the ILIM feature is useful is when
the device goes into continuous mode operation. This
occurs in step-up mode when
IL
ON
SWITCH
OFF
1073 F10
Figure 10. No Current Limit Causes
Large Inductor Current Build-Up
10
VOUT + VDIODE
1
<
VIN – VSW
1 – DC
When the input and output voltages satisfy this relationship, 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
oversizing the output capacitor and inductor. With the ILIM
feature, however, the switch current turns off at a programmed level as shown in Figure 11, keeping output
ripple to a minimum.
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.
The gain block itself is a very simple PNP input op amp with
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.
Arrangement of the gain block as a low battery detector is
straightforward. Figure 12 shows hookup. R1 and R2 need
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
IL
reduces the comparator hysteresis by the gain of the gain
ON
block. Output
ripple
can be reduced to just a few millivolts
SWITCH
OFF
using this technique. Ripple reduction works with stepdown or inverting modes as well.
1073 F11
Figure 11. Current Limit Keeps Inductor Current Under Control
LT1073
U
W
U U
APPLICATIO S I FOR ATIO
L1
VOUT
5V
VIN
R1
VBAT
212mV
REF
SET
R3
680k
LT1073
100k
–
A0
ILIM
VIN
AO
SW1
TO
PROCESSOR
+
FB
VBAT
+
C1
SET
GND
SW2
R1
V
LB
( 212mV
–1)
R1 = R2
R2
LT1073
R2
GND
D1
Table 2. Inductor Manufacturers
)(
(
1073 F12
Figure 12. Settling Low Battery Detector Trip Point
1073 F13
VOUT = R2 + 1 212mV
R1
VLB = BATTERY TRIP POINT
)
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
716-532-2234
GA10 Series
GA40 Series
Sanyo Video Components
1201 Sanyo Avenue
San Diego, CA 92073
619-661-6322
OS-CON Series
Caddell-Burns
258 East Second Street
Mineola, NY 11501
516-746-2310
7300 Series
6860 Series
Nichicon America Corporation
927 East State Parkway
Schaumberg, IL 60173
708-843-7500
PL Series
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
L1†
120µH
1N5818
1.5V
CELL
VIN
L1†
120µH
3V OUTPUT
20mA AT
VBATTERY = 1V
220Ω
ILIM
1.5V to 9V Step-Up Converter
ILIM
536k*
+
SW1
100µF
LT1073
1.5V
CELL
SW2
* 1% METAL FILM
†
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
VIN
9V OUTPUT
7mA AT VBATTERY = 1V
16mA AT VBATTERY = 1.5V
1M*
+
SW1
47µF
LT1073
FB
FB
GND
1N5818
GND
SW2
40.2k*
1073 TA03
* 1% METAL FILM
†
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
24.3k*
1073 TA04
11
LT1073
U
TYPICAL APPLICATIO S
1.5V to 12V Step-Up Converter
L1†
120µH
L1†
68µH
12V OUTPUT
5mA AT VBATTERY = 1V
16mA AT VBATTERY = 1.5V
ILIM
+
SW1
TWO
1.5V
CELLS
47µF
LT1073-12
†
5V OUTPUT
100mA AT
VBATTERY = 2V
VIN
+
SW1
100µF
LT1073-5
SENSE
SENSE
GND
1N5818
100Ω
VIN
ILIM
1.5V
CELL
1N5818
3V to 5V Step-Up Converter
GND
SW2
†
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
1073 TA05
SW2
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
3V to 12V Step-Up Converter
3V to 15V Step-Up Converter
†
L1
68µH
1N5818
L1†
68µH
12V OUTPUT
35mA AT
VBATTERY = 2V
100Ω
1073 TA06
1N5818
15V OUTPUT
27mA AT
VBATTERY = 2V
100Ω
1M*
ILIM
VIN
ILIM
+
SW1
TWO
1.5V
CELLS
TWO
1.5V
CELLS
47µF
LT1073-12
SENSE
GND
†
VIN
47µF
FB
SW2
GND
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
1073 TA07
SW2
L1†
150µH
1N5818
12V OUTPUT
130mA AT 4.5VIN
5VIN
LT1073-12
1M*
ILIM
+
100µF
+
100µF
SENSE
GND
+
SW1
SW2
L1 = GOWANDA GA20-153k
OR CADDELL-BURNS 7200-15
VIN
100µF
LT1073
FB
GND
†
15V OUTPUT
100mA AT 4.5VIN
50Ω
VIN
SW1
100µF
1N5818
5VIN
50Ω
+
1073 TA08
5V to 15V Step-Up Converter
†
L1
150µH
14.3k*
* 1% METAL FILM
†
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
5V to 12V Step-Up Converter
ILIM
+
SW1
LT1073
SW2
14.3k*
1073 TA09
* 1% METAL FILM
† L1 = GOWANDA GA20-153k
OR CADDELL-BURNS 7200-15
12
1073 TA10
LT1073
U
TYPICAL APPLICATIO S
1.5V to 5V Step-Up Converter with Logic Shutdown
L1†
82µH
1.5V to 5V Step-Up Converter with Low-Battery Detector
L1†
82µH
1N5818
1N5818
5V OUTPUT
5V OUTPUT
909k*
ILIM
1.5V
CELL
+
SW1
1.5V
CELL
442k*
VIN
100µF
LT1073
100k
ILIM
VIN
SET
SW1
+
100µF
LT1073-5
100k*
FB
GND
AO
SW2
40.2k*
1N4148
1073 TA11
OPERATE
SW2
LO BAT
GOES LOW
AT VBATTERY
= 1.15V
* 1% METAL FILM
†
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
74C04
SHUTDOWN
SENSE
GND
1073 TA12
* 1% METAL FILM
†
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
9V to 5V Step-Down Converter
9V to 3V Step-Down Converter
3V OUTPUT
220Ω
220Ω
ILIM
VIN
ILIM
536k*
VIN
SW1
SW1
LT1073-5
LT1073
9V
BATTERY
9V
BATTERY
FB
GND
L1†
100µH
SW2
+
†
* 1% METAL FILM
L1 = GOWANDA GA10-103k
OR CADDELL-BURNS 7300-13
1073 TA13
1073 TA14
Memory Backup Supply
5V TO MEMORY,
4.5V WHEN MAIN
SUPPLY OPEN
5V MAIN
SUPPLY
†
1N5818
5V OUTPUT
50mA
L1†
82µH
2N3906
1.5V
CELL
100µF
L1 = GOWANDA GA10-103k
OR CADDELL-BURNS 7300-13
1.5V to 5V Bootstrapped Step-Up Converter
2.2k
L1†
100µH
1N5818
100µF
†
L1
47µH
SW2
40.2k*
+
1N5818
5V OUTPUT
SENSE
GND
1N5818
56Ω
ILIM
VIN
ILIM
+
100µF
SW1
1.5V
CELL
LT1073-5
+
100µF**
FB
GND
SW2
†
L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
MINIMUM START-UP VOLTAGE = 1.1V
806k*
LT1073
SENSE
GND
VIN
SW1
1073 TA15
SW2
* 1% METAL FILM
**OPTIONAL
†
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
40.2k*
1073 TA16
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
100k
909k*
100Ω
100k
2N3906
3V
ILIM
VIN
AO
SW1
SET
+
100k*
ILIM
VIN
FB
SW1
1.5V
100µF
AO
SW2
40.3k*
* 1% METAL FILM
L1 = GOWANDA GA10-682k
OR CADDELL-BURNS 7300-11
909k*
+
SW2
40.2k*
* 1% METAL FILM
†
L1 = GOWANDA GA10-822k
OR CADDELL-BURNS 7300-12
1073 TA17
1.5V to 5V Very Low Noise Step-Up Converter
1073 TA18
9V to 5V Reduced Noise Step-Down Converter
L1†
47µH
†
L1
470µH
1N5818
5V OUTPUT
5mA AT VBATTERY = 1V
10mVP-P RIPPLE
680k
ILIM
VIN
FB
SW1
1.5V
AO
680k
+
100µF
OS-CON
LT1073
AO
GND
SET
SW2
40.2k*
40.2k*
1073 TA20
* 1% METAL FILM
L1 = GOWANDA GA10-473k
OR CADDELL-BURNS 7300-21
EFFICIENCY = 83% AT 5mA LOAD
†
* 1% METAL FILM
†
L1 = GOWANDA GA10-472k
OR CADDELL-BURNS 7300-09
1073 TA19
3V to 6V at 1A Step-Up Converter
INPUT
3V TO 6V
(2 LITHIUM CELLS)
L1†
25µH
EFFICIENCY ≈ 80%
IQ ≈ 130µA
OUTPUT NOISE ≈ 100mVP-P
1.5V Powered 350ps Risetime Pulse Generator
6V OUTPUT
1A AT
VIN = 3V
MUR120
†
L1
150µH
1.5V
560k
549k*
ILIM
VIN
FB
SW1
+
1N5820
AO
GND
ILIM
VIN
MTP3055EL
GND
OUTPUT
5V INTO
50Ω PULSE
WIDTH ≈ 1ns
SW2
24k
10k
50Ω
†
L1 = TOKO 262LYF-0095K
SELECT Q1 AND C1 FOR OPTIMUM RISE AND FALL
5.1k
†
14
C1
2pF TO 4pF
Q1
2N2369
FB
51Ω
2N3906
* 1% METAL FILM
L1 = COILTRONICS CTX25-5-52
LOW IQ (<250µA)
MUR120
0.1µF
LT1073
20k*
1M
SW1
SW2
1N5818
0.1µF
10M
2200µF
SET
0.1µF MUR120
90V BIAS
220Ω
+
LT1073
1000µF
909k*
1N5818
FB
100µF
OS-CON
SET
SW2
5VOUT
90mA AT 6.5VIN
220Ω
ILIM VIN SW1
LT1073
GND
+VIN
6.5V TO 12V
909k*
+
100µF
OS-CON
SET
GND
†
5V OUTPUT
20mVP-P RIPPLE
LT1073
FB
GND
1N5818
680k
1M*
LT1073
2.2M
L1†
82µH
5V OUTPUT
100mA
LOCKOUT
AT 1.8V
1N5818
1073 TA21
1073 TA22
LT1073
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.300 – 0.325
(7.620 – 8.255)
0.009 – 0.015
(0.229 – 0.381)
(
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
0.065
(1.651)
TYP
+0.035
0.325 –0.015
+0.889
8.255
–0.381
0.400*
(10.160)
MAX
)
8
7
6
5
1
2
3
4
0.255 ± 0.015*
(6.477 ± 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)
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
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
(0.406 – 1.270)
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
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
8
7
6
5
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
SO8 1298
1
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.
2
3
4
15
LT1073
U
TYPICAL APPLICATIO S
1.5V Powered Temperature Compensated Crystal Oscillator
L1†
820µH
1.5V
30.1k*
27.4k*
150k*
+
LT1017
150k
1.5V
–
6.81K*
ILIM
VIN
FB
SW1
1k
LT1073
A0
SET
LM134-3
SW2
1.5V
1.5V
2N3906
100k
2N3906
1N4148
150k*
73.2k*
+
+
47µF
100Ω
100k
39.2k*
47µF
10M*
2N3904
OUTPUT
1MHz
0.05ppm/°C
0.02µF
* 1% METAL FILM
L1 = J.W. MILLER #100267
= AT CUT –35° 20' ANGLE
510pF
2k
†
100k
1MHz
560k
MV209
510pF
1073 TA23
1.5V Powered α, β, γ Particle Detector
3 T1 10
1M
3M
1N976
330Ω
1N4148
X1
2N3906
2N3904
ILIM
VIN
FB
SW1
10k
AO
GND
D1
NC
D3
0.01µF
SET
SW2
NC
7
1
0.01µF
2
1M
68pF
600V
1N5818
T1 = COILTRONICS CTX10052-1
X1 = PROJECTS UNLIMITED AT11k OR 8Ω SPEAKER
D1, D2, D3 = MUR1100
R1 = VICTOREEN MOX-300
U1 = LND-712 CORP., OCEANSIDE, NY
D2
4
5
NC
LT1073
1.5V
0.01µF
500V
REGULATED
10M
1073 TA24
0.01µF
210k
R1
500M
U1
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1307
Single Cell Micropower 600kHz PWM DC/DC Converter
3.3V at 75mA from One Cell, MSOP Package
TM
LT1316
Burst Mode Operation DC/DC with Programmable Current Limit
1.5V Minimum, Precise Control of Peak Current Limit
LT1317
2-Cell Micropower DC/DC with Low-Battery Detector
3.3V at 200mA from Two Cells, 600kHz Fixed Frequency
LT1610
Single Cell Micropower DC/DC Converter
3V at 30mA from 1V, 1.7MHz Fixed Frequency
LT1611
Inverting 1.4MHz Switching Regulator in 5-Lead SOT-23
–5V at 150mA from 5V Input, Tiny SOT-23 Package
LT1613
1.4MHz Switching Regulator in 5-Lead SOT-23
5V at 200mA from 3.3V Input, Tiny SOT-23 Package
LT1615
Micropower Constant Off-Time DC/DC Converter in 5-Lead SOT-23
20V at 12mA from 2.5V, Tiny SOT-23 Package
LT1617
Micropower Inverting DC/DC Converter in 5-Lead SOT-23
–15V at 12mA from 2.5V, Tiny SOT-23 Package
LT1930/LT1930A 1.2MHz/2.2MHz, 1A Switching Regulator in 5-Lead SOT-23
5V at 450mA from 3.3V Input, Tiny SOT-23 Package
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.
16
Linear Technology Corporation
1073fa LT/TP 0301 2K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 2000
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