|
|
PDF LTC1701ES5 Data sheet ( Hoja de datos )
| Número de pieza | LTC1701ES5 | |
| Descripción | 1MHz Step-Down DC/DC Converter in SOT-23 | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC1701ES5 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
Final Electrical Specifications
LTC1701
1MHz Step-Down
DC/DC Converter in SOT-23
December 1999
FEATURES
DESCRIPTIO
s Tiny 5-Lead SOT-23 Package
s Uses Tiny Capacitors and Inductor
s High Frequency Operation: 1MHz
s High Output Current: 500mA
s Low RDS(ON) Internal Switch: 0.28Ω
s High Efficiency: Up to 94%
s Current Mode Operation for Excellent Line
and Load Transient Response
s Short-Circuit Protected
s Low Quiescent Current: 135µA
s Low Dropout Operation: 100% Duty Cycle
s Ultralow Shutdown Current: IQ < 1µA
s Peak Inductor Current Independent of Inductor Value
s Output Voltages from 5V Down to 1.25V
U
APPLICATIO S
s PDAs/Palmtop PCs
s Digital Cameras
s Cellular Phones
s Portable Media Players
s PC Cards
s Handheld Equipment
The LTC®1701 is the industry’s first 5-lead SOT-23 step
down, current mode, DC/DC converter. Intended for small
to medium power applications, it operates from 2.5V to
5.5V input voltage range and switches at 1MHz, allowing
the use of tiny, low cost capacitors and inductors 2mm or
less in height. The output voltage is adjustable from 1.25V
to 5V. A built-in 0.28Ω switch allows up to 0.5A of output
current at high efficiency. OPTI-LOOPTM compensation
allows the transient response to be optimized over a wide
range of loads and output capacitors.
The LTC1701 incorporates automatic power saving Burst
ModeTM operation to reduce gate charge losses when the
load current drops below the level required for continuous
operation. With no load, the converter draws only 135µA.
In shutdown, it draws less than 1µA, making it ideal for
current sensitive applications.
In dropout, the internal P-channel MOSFET switch is
turned on continuously, thereby maximizing battery life.
Its small size and switching frequency enables the com-
plete DC/DC converter function to consume less than 0.3
square inches of PC board area.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
2.5V TO
5.5V
C1 +
10µF
VIN SW
R4
1M LTC1701
ITH/RUN
R3 GND
5.1k
C3
330pF
VFB
L1
4.7µH
D1
R2
121k
+
R1
121k
C1: TAIYO YUDEN JMK316BJ106ML
C2: SANYO POSCAP 6TPA47M
D1: MBRM120L
L1: SUMIDA CD43-4R7
Figure 1. Step-Down 2.5V/500mA Regulator
VOUT
(2.5V/
500mA)
C2
47µF
1701 F01
Efficiency Curve
100
VIN = 3.3V
95
90
85
80
75
70
1 10 100
LOAD CURRENT (mA)
1000
1701 F01a
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
1 page  
LTC1701
APPLICATIO S I FOR ATIO
where VD is the output Schottky diode forward drop.
Accepting larger values of ∆IL allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ∆IL = 0.4A.
The inductor value also has an effect on low current
operation. Lower inductor values (higher ∆IL) will cause
Burst Mode operation to begin at higher load currents,
which can cause a dip in efficiency in the upper range of
low current operation. In Burst Mode operation, lower
inductance values will cause the burst frequency to de-
crease.
Inductor Core Selection
Once the value for L is selected, the type of inductor must
be chosen. Basically, there are two kinds of losses in an
inductor —core and copper losses.
Core losses are dependent on the peak-to-peak ripple
current and core material. However, it is independent of
the physical size of the core. By increasing inductance, the
peak-to-peak inductor ripple current will decrease, there-
fore reducing core loss. Unfortunately, increased induc-
tance requires more turns of wire and, therefore, copper
losses will increase. When space is not a premium, larger
wire can be used to reduce the wire resistance. This also
prevents excessive heat dissipation in the inductor.
High efficiency converters generally cannot afford the core
loss found in low cost powdered iron cores, forcing the
use of more expensive ferrite, molypermalloy or Kool Mµ®
cores. These low core loss materials allow the user to
concentrate on reducing copper loss and preventing satu-
ration.
Ferrite designs have very low core loss and are preferred
at high switching frequencies. Ferrite core material satu-
rates “hard,” which means that inductance collapses
abruptly when the peak design current is exceeded. This
results in an abrupt increase in inductor ripple current and
consequent output voltage ripple. Do not allow the core to
saturate!
Molypermalloy (from Magnetics, Inc.) is a very good, low
loss core material for toroids, but it is more expensive than
ferrite. A reasonable compromise from the same manu-
facturer is Kool Mµ core material. Toroids are very space
efficient, expecially when you can use several layers of
wire. Because they generally lack a bobbin, mounting is
more difficult. However, surface mount designs that do
not increase the height significantly are available
Catch Diode Selection
The diode D1 shown in Figure 1 conducts during the off-
time. It is important to adequately specify the diode peak
current and average power dissipation so as not to exceed
the diode ratings.
Losses in the catch diode depend on forward drop and
switching times. Therefore, Schottky diodes are a good
choice for low drop and fast switching times.
Since the catch diode carries the load current during the
off-time, the average diode current is dependent on the
switch duty cycle. At high input voltages, the diode con-
ducts most of the time. As VIN approaches VOUT, the diode
conducts only a small fraction of the time. The most
stressful condition for the diode is when the regulator
output is shorted to ground.
Under short-circuit conditions (VOUT = 0V), the diode
must safely handle ISC(PK) at close to 100% duty cycle.
Under normal load conditions, the average current con-
ducted by the diode is simply:
IDIODE(avg)
=
ILOAD(avg)
VIN − VOUT
VIN + VD
Remember to keep lead lengths short and observe proper
grounding (see Board Layout Considerations) to avoid
ringing and increased dissipation.
The forward voltage drop allowed in the diode is calculated
from the maximum short-circuit current as:
VD
≈
PD
ISC(avg)
VIN + VD
VIN
where PD is the allowable diode power dissipation and will
be determined by efficiency and/or thermal requirements
(see Efficiency Considerations).
Kool Mµ is a registered trademark of Magnetics, Inc.
5
5 Page 
TYPICAL APPLICATIO S
5V to 3.3V Converter with Push-Button On/Off
L1
4.7µH
VIN
5V
VIN SW
+
C1
15µF
ON
C4
1µF
R4
1M
R5 R3
OFF 5.1M 5.1k
C1: AVX TAJA156M010R
C2: AVX TAJA226M006R
C4: TAIYO YUDEN LMK212BJ105MG
C5: TAIYO YUDEN JMK212BJ475MG
D1: MBRM120L
L1: MURATA LQH3C4R7M24
LTC1701
ITH/RUN
VFB
GND
C3
330pF
D1
R2
34k
R1
20.5k
+
C2
22µF
LTC1701
VOUT
(3.3V/0.5A)
C5
4.7µF
1701 TA03
PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted.
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
2.80 – 3.00
(0.110 – 0.118)
(NOTE 3)
2.60 – 3.00
(0.102 – 0.118)
1.50 – 1.75
(0.059 – 0.069)
1.90
(0.074)
REF
0.00 – 0.15
(0.00 – 0.006)
0.95
(0.037)
REF
0.90 – 1.45
(0.035 – 0.057)
0.35 – 0.55
(0.014 – 0.022)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.35 – 0.50
0.90 – 1.30
(0.014 – 0.020) (0.035 – 0.051)
FIVE PLACES (NOTE 2)
S5 SOT-23 0599
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DIMENSIONS ARE INCLUSIVE OF PLATING
3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
4. MOLD FLASH SHALL NOT EXCEED 0.254mm
5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC1701ES5.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC1701ES5 | 1MHz Step-Down DC/DC Converter in SOT-23 | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |