|
|
PDF LT1767-2.5 Data sheet ( Hoja de datos )
| Número de pieza | LT1767-2.5 | |
| Descripción | 1.25MHz Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT1767-2.5 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
|
No Preview Available !
LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
Monolithic 1.5A, 1.25MHz
Step-Down Switching Regulators
Features
n 1.5A Switch in a Small MSOP Package
n Constant 1.25MHz Switching Frequency
n High Power Exposed Pad (MS8E) Package
n Wide Operating Voltage Range: 3V to 25V
n High Efficiency 0.22Ω Switch
n 1.2V Feedback Reference Voltage
n Fixed Output Voltages of 1.8V, 2.5V, 3.3V, 5V
n 2% Overall Output Tolerance
n Uses Low Profile Surface Mount Components
n Low Shutdown Current: 6µA
n Synchronizable to 2MHz
n Current Mode Loop Control
n Constant Maximum Switch Current Rating at All Duty
Cycles*
Applications
n DSL Modems
n Portable Computers
n Wall Adapters
n Battery-Powered Systems
n Distributed Power
Description
The LT®1767 is a 1.25MHz monolithic buck switching
regulator. A high efficiency 1.5A, 0.22Ω switch is included
on the die together with all the control circuitry required
to complete a high frequency, current mode switching
regulator. Current mode control provides fast transient
response and excellent loop stability.
New design techniques achieve high efficiency at high
switching frequencies over a wide operating range. A
low dropout internal regulator maintains consistent per-
formance over a wide range of inputs from 24V systems
to Li-Ion batteries. An operating supply current of 1mA
improves efficiency, especially at lower output currents.
Shutdown reduces quiescent current to 6µA. Maximum
switch current remains constant at all duty cycles. Syn-
chronization allows an external logic level signal to increase
the internal oscillator from 1.5MHz to 2MHz.
The LT1767 is available in an 8-pin MSOP fused lead-frame
package and a low thermal resistance exposed pad package.
Full cycle-by-cycle current limit and thermal shutdown are
provided. High frequency operation allows the reduction
of input and output filtering components and permits the
use of chip inductors.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 6611131, 6498466.
Typical Application
12V to 3.3V Step-Down Converter
D2
CMDSH-3
VIN
12V C3
2.2µF
CERAMIC
OPEN
OR
HIGH
= ON
C2
0.1µF
BOOST
VIN VSW
LT1767-3.3
SHDN
FB
SYNC GND VC
CC
1.5nF
RC
4.7k
L1
5µH
D1
UPS120
*MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.
OUTPUT
3.3V
1.2A*
C1
10µF
CERAMIC
1767 TA01
For more information www.linear.com/LT1767
Efficiency vs Load Current
95
VIN = 10V
90 VOUT = 5V
85
80
75
70
0 0.2 0.4 0.6 0.8 1 1.2 1.4
LOAD CURRENT (A)
1767 TA01a
1767fb
1
1 page  
LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
TYPICAL PERFORMANCE Characteristics TA = 25°C, unless otherwise noted.
MMiinniimmuumm IInnppuutt VVoollttaaggee,, 33..33VV OOuutt
7.0
6.5
BOOST DIODE TIED TO VOUT
BOOST DIODE TIED TO VIN
6.0
5.5
5.0 TO START
4.5
SHDN Supply Current
300
VIN = 15V
250
200
150
Input Supply Current
1200
1000
800
600
MINIMUM
INPUT
VOLTAGE
4.0 100 400
3.5
3.0 TO RUN
50
200
2.5
1
10 100
LOAD CURRENT (mA)
1k
1767 G07
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
SHUTDOWN VOLTAGE (V)
1767 G08
0
0 5 10 15 20
INPUT VOLTAGE (V)
25 30
1767 G09
Current Limit Foldback
2.0
Maximum Load Current,
VOUT = 5V
40 1.5
Maximum Load Current,
VOUT = 2.5V
1.5
1.5 30
SWITCH CURRENT
1.0 20
0.5 10
FB CURRENT
00
0 0.2 0.4 0.6 0.8 1 1.2
FEEDBACK VOLTAGE (V)
1767 G10
1.3
1.1
0.9
0.7
0.5
0
L = 4.7µH
L = 2.2µH
L = 1.5µH
5 10 15 20
INPUT VOLTAGE (V)
25
1767 G11
1.3
1.1
0.9
0.7
0
L = 4.7µH
L = 2.2µH
L = 1.5µH
5 10 15 20
INPUT VOLTAGE (V)
25
1767 G12
For more information www.linear.com/LT1767
1767fb
5
5 Page 
LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
APPLICATIONS INFORMATION
CATCH DIODE
The suggested catch diode (D1) is a UPS120 Schottky, or
its Motorola equivalent, MBRM120LTI/MBRM130LTI. It is
rated at 2A average forward current and 20V/30V reverse
voltage. Typical forward voltage is 0.5V at 1A. The diode
conducts current only during switch off time. Peak reverse
voltage is equal to regulator input voltage. Average forward
current in normal operation can be calculated from:
( )
ID(AVG) = IOUT
VIN − VOUT
VIN
Shutdown and Undervoltage Lockout
Figure 4 shows how to add undervoltage lockout (UVLO)
to the LT1767. Typically, UVLO is used in situations where
the input supply is current limited, or has a relatively high
source resistance. A switching regulator draws constant
power from the source, so source current increases as
source voltage drops. This looks like a negative resistance
load to the source and can cause the source to current limit
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where these problems might occur.
BOOST PIN
For most applications, the boost components are a 0.1µF
capacitor and a CMDSH-3 diode. The anode is typically
connected to the regulated output voltage to generate
a voltage approximately VOUT above VIN to drive the
output stage. The output driver requires at least 2.7V of
headroom throughout the on period to keep the switch
fully saturated. However, the output stage discharges the
boost capacitor during the on time. If the output voltage is
less than 3.3V, it is recommended that an alternate boost
supply is used. The boost diode can be connected to the
input, although, care must be taken to prevent the 2x VIN
boost voltage from exceeding the BOOST pin absolute
maximum rating. The additional voltage across the switch
driver also increases power loss, reducing efficiency. If
available, an independent supply can be used with a local
bypass capacitor.
A 0.1µF boost capacitor is recommended for most ap-
plications. Almost any type of film or ceramic capacitor
is suitable, but the ESR should be <1Ω to ensure it can
be fully recharged during the off time of the switch. The
capacitor value is derived from worst-case conditions of
700ns on-time, 50mA boost current, and 0.7V discharge
ripple. This value is then guard banded by 2x for secondary
factors such as capacitor tolerance, ESR and temperature
effects. The boost capacitor value could be reduced under
less demanding conditions, but this will not improve cir-
cuit operation or efficiency. Under low input voltage and
low load conditions, a higher value capacitor will reduce
discharge ripple and improve start up operation.
LT1767
VIN IN
7µA
1.33V
R1 3µA
SHDN
C1 R2
GND
OUTPUT
VSW
VCC +
Figure 4. Undervoltage Lockout
1767 F04
An internal comparator will force the part into shutdown
below the minimum VIN of 2.6V. This feature can be
used to prevent excessive discharge of battery-operated
systems. If an adjustable UVLO threshold is required, the
shutdown pin can be used. The threshold voltage of the
shutdown pin comparator is 1.33V. A 3µA internal current
source defaults the open pin condition to be operating (see
Typical Performance Graphs). Current hysteresis is added
above the SHDN threshold. This can be used to set voltage
hysteresis of the UVLO using the following:
R1=
VH − VL
7µA
R2 =
(VH
1.33V
− 1.33V)
R1
+
3µA
VH – Turn-on threshold
VL – Turn-off threshold
For more information www.linear.com/LT1767
1767fb
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT1767-2.5.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT1767-2.5 | 1.25MHz Step-Down Switching Regulators | 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 |