|
|
PDF LT1940L Data sheet ( Hoja de datos )
| Número de pieza | LT1940L | |
| Descripción | 1.1MHz Step-Down Switching Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT1940L (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
|
No Preview Available !
FEATURES
s Wide Input Voltage Range
LT1940: 3.6V to 25V
LT1940L: 3.6V to 7V
s Two 1.4A Output Switching Regulators with
Internal Power Switches
s Constant 1.1MHz Switching Frequency
s Anti-Phase Switching Reduces Ripple
s Independent Shutdown/Soft-Start Pins
s Independent Power Good Indicators Ease
Supply Sequencing
s Uses Small Inductors and Ceramic Capacitors
s Small 16-Lead Thermally Enhanced
TSSOP Surface MUount Package
APPLICATIO S
s Disk Drives
s DSP Power Supplies
s Wall Transformer Regulation
s Distributed Power Regulation
s DSL Modems
s Cable Modems
, LTC and LT are registered trademarks of Linear Technology Corporation.
LT1940/LT1940L
Dual Monolithic 1.4A,
1.1MHz Step-Down
Switching Regulator
DESCRIPTIO
The LT®1940 is a dual current mode PWM step-down
DC/DC converter with internal 2A power switches. Both con-
verters are synchronized to a single 1.1MHz oscillator and
run with opposite phases, reducing input ripple current. The
output voltages are set with external resistor dividers, and
each regulator has independent shutdown and soft-start
circuits. Each regulator generates a power-good signal
when its output is in regulation, easing power supply se-
quencing and interfacing with microcontrollers and DSPs.
The LT1940’s 1.1MHz switching frequency allows the use
of tiny inductors and capacitors, resulting in a very small
dual 1.4A output solution. Constant frequency and ceramic
capacitors combine to produce low, predictable output
ripple voltage. With its wide input range of 3.6V to 25V, the
LT1940 regulates a wide variety of power sources, from
4-cell batteries and 5V logic rails to unregulated wall trans-
formers, lead acid batteries and distributed-power supplies.
The LT1940L is intended to operate from regulated 5V
supplies. A current mode PWM architecture provides fast
transient response with simple compensation components
and cycle-by-cycle current limiting. Frequency foldback and
thermal shutdown provide additional protection.
TYPICAL APPLICATIO
VIN
7V TO 25V
4.7µF
CMDSH-3
VIN
BOOST1 BOOST2
OUT1
3.3V
1.4A
0.1µF
3.3µH
UPS140
16.5k
LT1940
SW1 SW2
FB1 FB2
CMDSH-3
0.1µF
4.7µH
UPS140
30.1k
OUT2
5V
1.4A
10.0k
15k
VC1
RUN/SS1
VC2
PG1
15k 10.0k
10µF
10µF
330pF
1nF
RUN/SS2
PG2
GND
330pF
100k
POWER
1940 F01 GOOD
Figure 1. 3.3V and 5V Dual Output Step-Down Converter with Output Sequencing (LT1940)
Efficiency vs Load Current
100
VIN = 12V
90
VOUT = 5V
80
VOUT = 3.3V
70
60
0
0.5 1.0
LOAD CURRENT (A)
1.5
1940 F01b
1940fa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
RUN/SS Thresholds vs
Temperature
1.4
1.2
1.0
TO SWITCH
0.8
0.6
TO RUN
0.4
0.2
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1940 G13
Minimum Input Voltage,
VOUT = 3.3V
6.0
5.5
VIN TO START
TA = 25°C
DBOOST = BAT54
5.0
4.5
4.0
VIN TO RUN
3.5
BOOST DIODE
TIED TO OUTPUT
BOOST DIODE
TIED TO INPUT
3.0
1
10 100
LOAD CURRENT (mA)
1000
1940 G14
LT1940/LT1940L
Minimum Input Voltage,
VOUT = 5V
7.5
7.0 VIN TO START
TA = 25°C
DBOOST = BAT54
6.5
6.0
5.5
VIN TO RUN
5.0
BOOST DIODE
TIED TO OUTPUT
BOOST DIODE
TIED TO INPUT
4.5
1
10 100
LOAD CURRENT (mA)
1000
1940 G14
PI FU CTIO S
BOOST1, BOOST2 (Pins 1, 8): The BOOST pins are used
to provide drive voltages, higher than the input voltage, to
the internal bipolar NPN power switches.Tie through a
diode from VOUT or from VIN.
SW1, SW2 (Pins 2, 7): The SW pins are the outputs of the
internal power switches. Connect these pins to the induc-
tors, catch diodes and boost capacitors.
VIN (Pins 3, 4, 5, 6): The VIN pins supply current to the
LT1940’s internal regulator and to the internal power
switches. These pins must be tied to the same source, and
must be locally bypassed.
FB1, FB2 (Pins 9, 16): The LT1940 regulates each feed-
back pin to 1.25V. Connect the feedback resistor divider
taps to these pins.
VC1, VC2 (Pins 10, 15): The VC pins are the outputs of the
internal error amps. The voltages on these pins control the
peak switch currents. These pins are normally used to
compensate the control loops, but can also be used to
override the loops. Pull these pins to ground with an open
drain to shut down each switching regulator.
PG1, PG2 (Pins 11, 14): The Power Good pins are the
open collector outputs of an internal comparator. PG
remains low until the FB pin is within 10% of the final
regulation voltage. As well as indicating output regulation,
the PG pins can be used to sequence the two switching
regulators. These pins can be left unconnected. The PG
outputs are valid when VIN is greater than 2.4V and either
of the RUN/SS pins is high. The PG comparators are
disabled in shutdown.
RUN/SS1, RUN/SS2 (Pins 12, 13): The RUN/SS pins are
use to shut down the individual switching regulators and
the internal bias circuits. They also provide a soft-start
function. To shut down either regulator, pull the RUN/SS
pin to ground with an open drain or collector. Tie a
capacitor from these pins to ground to limit switch current
during start-up. If neither feature is used, leave these pins
unconnected.
GND (Pin 17): The Exposed Pad of the package provides
both electrical contact to ground and good thermal con-
tact to the printed circuit board. The Exposed Pad must be
soldered to the circuit board for proper operation.
1940fa
5
5 Page 
LT1940/LT1940L
APPLICATIO S I FOR ATIO
Table 2. Low-ESR Surface Mount Capacitors
Vendor
Type
Series
Taiyo Yuden
Ceramic X5R, X7R
AVX Ceramic X5R, X7R
Tantalum
TPS
Kemet
Tantalum
Ta Organic
Al Organic
T491,T494,T495
T520
A700
Sanyo
Ta or Al Organic
POSCAP
Panasonic
Al Organic
SP CAP
TDK Ceramic X5R, X7R
Catch Diode
Use a 1A Schottky diode for the catch diode (D1 in
Figure 2). The diode must have a reverse voltage rating
greater than the maximum input voltage. The ON Semi-
conductor MBRM120LT3 (20V) and MBRM130LT3 (30V)
are good choices; they have a tiny package with good
thermal properties. Many vendors have surface mount
versions of the 1N5817 (20V) and 1N5818 (30V) 1A
Schottky diodes such as the Microsemi UPS120 that are
suitable.
Boost Pin Considerations
The capacitor and diode tied to the BOOST pin generate a
voltage that is higher than the input voltage. In most cases
a 0.1µF capacitor and fast switching diode (such as the
CMDSH-3 or FMMD914) will work well. Figure 3 shows
three ways to arrange the boost circuit. The BOOST pin
must be more than 2.5V above the SW pin for full effi-
ciency. For outputs of 3.3V and higher the standard circuit
(Figure 3a) is best. For outputs between 2.8V and 3.3V,
use a small Schottky diode (such as the BAT-54). For lower
output voltages the boost diode can be tied to the input
(Figure␣ 3b). The circuit in Figure 3a is more efficient
because the BOOST pin current comes from a lower
voltage source. Finally, as shown in Figure 3c, the anode
of the boost diode can be tied to another source that is at
least 3V. For example, if you are generating 3.3V and 1.8V
and the 3.3V is on whenever the 1.8V is on, the 1.8V boost
diode can be connected to the 3.3V output. In any case,
you must also be sure that the maximum voltage at the
BOOST pin is less than the maximum specified in the
Absolute Maximum Ratings section.
D2 D2
BOOST
C3
LT1940
VIN VIN SW
GND
VOUT
BOOST
C3
LT1940
VIN VIN SW
GND
VOUT
VIN2 > 3V
VIN
VBOOST – VSW ≅ VOUT
MAX VBOOST ≅ VIN + VOUT
(3a)
D2
BOOST
LT1940
VIN SW
GND
C3
VBOOST – VSW ≅ VIN2
MAX VBOOST ≅ VIN2 + VIN
MINIMUM VALUE FOR VIN2 = 3V
(3c)
VOUT
1940 F03
VIN2
>VIN + 3V
VIN
VBOOST – VSW ≅ VIN
MAX VBOOST ≅ 2VIN
D2
(3b)
BOOST
LT1940
VIN SW
GND
MAX VBOOST – VSW ≅ VIN2
MAX VBOOST ≅ VIN2
MINIMUM VALUE FOR VIN2 = VIN + 3V
(3d)
VOUT
1940 F03
Figure 3. Generating the Boost Voltage
1940fa
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT1940L.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT1940 | 1.1MHz Step-Down Switching Regulator |  Linear Technology |
| LT1940EFE | Dual Monolithic 1.4A/ 1.1MHz Step-Down Switching Regulator | Linear Technology |
| LT1940L | 1.1MHz Step-Down Switching Regulator | Linear |
| 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 |