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PDF LT1073CN8-5 Data sheet ( Hoja de datos )
| Número de pieza | LT1073CN8-5 | |
| Descripción | Micropower DC-DC Converter Ajustable and Fixed 5V/ 12V | |
| Fabricantes | Linear Technology | |
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FEATURES
s No Design Required
s Operates at Supply Voltages from 1V to 30V
s Consumes Only 95µA Supply Current
s Works in Step-Up or Step-Down Mode
s Only Three External Off-the-Shelf Components
Required
s Low-Battery Detector Comparator On-Chip
s User-Adjustable Current Limit
s Internal 1A Power Switch
s Fixed or Adjustable Output Voltage Versions
s Space-Saving 8-Pin PDIP or SO-8 Package
U
APPLICATIO S
s Pagers
s Cameras
s Single-Cell to 5V Converters
s Battery Backup Supplies
s Laptop and Palmtop Computers
s Cellular Telephones
s Portable Instruments
s 4mA to 20mA Loop Powered Instruments
s Hand-Held Inventory Computers
s Battery-Powered α, β, and γ Particle Detectors
LT1073
Micropower
DC/DC Converter
Adjustable and Fixed 5V, 12V
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.
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.
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
Single-Cell to 5V Converter
CADDELL-BURNS
7300-12
82µH 1N5818
5V
40mA
12
ILIM VIN
1.5V SW1 3
AA CELL* LT1073-5
SENSE 8
GND SW2
54
+ 100µF
SANYO
0S-CON
OPERATES WITH CELL VOLTAGE ≥1V
*ADD 10µF DECOUPLING CAPACITOR IF
BATTERY IS MORE THAN 2" AWAY FROM LT1073
1073 TA01
Single Alkaline “AA” Cell Operating
Hours vs DC Load Current
1000
100
10
1
1
L = 180µH
L = 82µH
10
LOAD CURRENT (mA)
100
LT1073 TA02
1
1 page  
U
OPERATIO
LT1073
The LT1073 is gated oscillator switcher. This type archi-
tecture 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 under-
stood by referring to the LT1073 Block Diagram. Com-
parator 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 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.
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.
LT1073
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
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 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.
( )VOUT
=
212mV
R2
R1
+ 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
considerably by using the gain block amp as a preamplifier
in front of the FB pin. See the Applications Information
section for details.
5
5 Page 
LT1073
APPLICATIO S I FOR ATIO
VBAT
212mV
R1 REF
SET
R2
VIN
–
+
LT1073
A0
5V
100k
TO
PROCESSOR
GND
( )R1 = R2
VLB
212mV
–1
VLB = BATTERY TRIP POINT
1073 F12
Figure 12. Settling Low Battery Detector Trip Point
Table 2. Inductor Manufacturers
MANUFACTURER
Gowanda Electronics Corporation
1 Industrial Place
Gowanda, NY 14070
716-532-2234
Caddell-Burns
258 East Second Street
Mineola, NY 11501
516-746-2310
Coiltronics International
984 S.W. 13th Court
Pompano Beach, FL 33069
305-781-8900
Toko America Incorporated
1250 Feehanville Drive
Mount Prospect, IL 60056
312-297-0070
Renco Electronics Incorporated
60 Jefryn Boulevard, East
Deer Park, NY 11729
800-645-5828
PART NUMBERS
GA10 Series
GA40 Series
7300 Series
6860 Series
Custom Toroids
Surface Mount
Type 8RBS
RL1283
RL1284
L1
R3
680k
VBAT
ILIM VIN
AO SW1
LT1073
FB SET
GND SW2
D1
VOUT
R2
+
C1
R1
( )( )VOUT =
R2
R1
+
1
212mV
1073 F13
Figure 13. Output Ripple Reduction Using Gain Block
Table 3. Capacitor Manufacturers
MANUFACTURER
Sanyo Video Components
1201 Sanyo Avenue
San Diego, CA 92073
619-661-6322
Nichicon America Corporation
927 East State Parkway
Schaumberg, IL 60173
708-843-7500
Sprague Electric Company
Lower Main Street
Stanford, ME 04073
207-324-4140
PART NUMBERS
OS-CON Series
PL Series
150D Solid Tantalums
550D Tantalex
TYPICAL APPLICATIO S
1.5V to 3V Step-Up Converter
L1†
120µH 1N5818
220Ω
3V OUTPUT
20mA AT
VBATTERY = 1V
ILIM VIN
1.5V
CELL
SW1
LT1073
FB
GND SW2
536k*
+
100µF
40.2k*
* 1% METAL FILM
† L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
1073 TA03
1.5V to 9V Step-Up Converter
L1†
120µH 1N5818
9V OUTPUT
7mA AT VBATTERY = 1V
16mA AT VBATTERY = 1.5V
1.5V
CELL
ILIM VIN
SW1
LT1073
FB
GND SW2
1M*
+
47µF
24.3k*
* 1% METAL FILM
† L1 = GOWANDA GA10-123k
OR CADDELL-BURNS 7300-14
1073 TA04
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1073CN8-5.PDF ] | |
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