|
|
PDF LT3742 Data sheet ( Hoja de datos )
| Número de pieza | LT3742 | |
| Descripción | 2-Phase Step-Down Switching Controller | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT3742 (archivo pdf) en la parte inferior de esta página. Total 26 Páginas | ||
|
No Preview Available !
Features
n Wide Input Voltage Range: 4V to 30V
n Wide Output Voltage Range: 0.8V to VIN
n Low Shutdown IQ: 20µA
n Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
n 0.8V ±1.5% Voltage Reference
n 500kHz Current Mode Fixed Frequency Operation
n Internal Boost Converter Provides Bias Rail for
N-channel MOSFET Gate Drive
n Power Good Voltage Monitor for Each Output
n Programmable Soft-Start
n 24-Lead 4mm × 4mm × 0.75mm Package
Applications
n Satellite and Cable TV Set-Top Boxes
n Distributed Power Regulation
n Automotive Systems
n Super Capacitor Charger
LT3742
Dual, 2-Phase Step-Down
Switching Controller
Description
The LT®3742 is a dual step-down DC/DC switching regulator
controller that drives high side N-channel power MOSFETs.
A 500kHz fixed frequency current mode architecture pro-
vides fast transient response with simple loop compensa-
tion components and cycle-by-cycle current limiting. The
output stages of the two controllers operate 180° out of
phase to reduce the input ripple current, minimizing the
noise induced on the input supply, and allowing less input
capacitance.
An internal boost regulator generates a bias rail of VIN + 7V
to provide gate drive for the N-channel MOSFETs allowing
low dropout and 100% duty cycle operation. The LT3742
can be used for applications where both controllers need
to operate independently, or where both controllers are
used to provide a single higher current output.
The device is available in a thermally enhanced 4mm ×
4mm QFN package.
L, LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase and Burst Mode are registered
trademarks and No RSENSE is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Typical Application
8V and 5V Dual Step-Down Converter
VIN
VOUT1
8V
4A
47µF
RUN1
VIN
10µH
4.7µF
14V
45.3k VIN
1µF UVLO
SWB BIAS
20.0k
10µF
0.010Ω 6.5µH
1.8k
200Ω
LT3742
G1 G2
SSSEWENN1SSEE11+–
FB1
SSEENNSSSEEW222+–
FB2
6.5µH 0.010Ω
1.05k
200Ω
VIN
10µF
VOUT2
5V
4A
47µF
1nF 1000pF
PG1 PG1
PG2 PG2
RUN/SS1 RUN/SS2
VC1 VC2
30k GND 20k
1000pF
1nF
RUN2
Efficiency vs Load Current
100 8VOUT
90
5VOUT
80
70
60
50
40
0 0.5 1 1.5 2 2.5 3 3.5 4
LOAD CURRENT (A)
3742 TA01b
3742 TA01a
3742fa
1
1 page  
Typical Performance Characteristics
Controller Frequency
vs Temperature
600
PG Threshold vs Temperature
1.0
550 0.9
500 0.8 POWER GOOD
450 0.7
LT3742
VBIAS – VIN vs Temperature
10
8
6
400
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3742 G09
SWB Current Limit
vs Temperature
380
360
340
320
0.6
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3742 G10
4
–50 –25
RUN/SS Threshold
vs Temperature
1.0
0 25 50 75
TEMPERATURE (°C)
100 125
3742 G11
0.7
0.4
300
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3742 G12
0.1
–25
0 25 50 75 100 125
TEMPERATURE (°C)
3742 G13
3742fa
5
5 Page 
LT3742
Applications Information
characteristic to notice about this method is that if the
output of controller 1 goes out of regulation enough
to trip the power good comparator, controller 2 will be
disabled.
In Figure 2b, a slightly larger capacitor on RUN/SS2 delays
the turn-on of controller 2 with respect to controller 1. The
start-up waveforms for this method look very similar to
the one shown in Figure 6a, but here controller 2 is not
disabled if controller 1 goes out of regulation.
In Figure 2c, both RUN/SS pins share a single capacitor
and start up at the same time. By sharing the same soft-
start signal, this method provides ratiometric tracking of
the two outputs.
Undervoltage Lockout (UVLO)
An external resistor divider can be used to accurately
set the minimum input voltage at which the LT3742 will
operate. Figure 3 shows the basic UVLO operation. Once
the UVLO pin drops below 1.25V, an undervoltage lock-
out event is signaled, turning on a 3µA current source to
provide hysteresis.
During a UVLO event, both controllers and the gate drive
boost regulator are disabled. For the LT3742, all RUN/SS
pins are discharged to get ready for a new soft-start cycle.
For each controller that is enabled, it’s RUN/SS pin will
be held to 500mV until the input voltage rises above the
upper UVLO trip voltage. The UVLO function is only active
when one or more of the controllers are enabled using the
RUN/SS pin. The UVLO pin can not be used to directly
start the part. Do not leave the UVLO pin unconnected;
tie it to VIN if not used. A separate, less accurate, internal
undervoltage lockout will disable the LT3742 when VIN is
less than 2.5V.
The UVLO resistor values are chosen to give the desired
minimum operating voltage (VIN(MIN)) and the desired
amount of hysteresis (VHYST). The LT3742 will turn on
when the input voltage is above (VIN(MIN) + VHYST), and
once on, will turn off when VIN drops below VIN(MIN). Select
the value for RUV1 first, then select the value for RUV2.
RUV1
=
VHYST
3µA
RUV 2
=
RUV1
•
1.25V
VIN(MIN) – 1.25V
Input Voltage Range
The minimum input voltage is determined by either the
LT3742’s minimum operating voltage of 4V, UVLO or by
the output voltages of a given application. The LT3742 can
operate at 100% duty cycle, so if the input voltage drops
close to or equal to one of the output voltages, the control-
ler will go into low dropout operation (100% duty cycle).
The duty cycle is the fraction of the time the N-channel
MOSFET is on every switch cycle, and is determined by
the input and output voltages:
DC
=
⎛
⎜
⎝
VOUT +
VIN – VDS
VD
+ VD
⎞
⎟
⎠
where VD is the forward drop of the catch diode (~0.4V)
and VDS is the typical MOSFET voltage drop (~0.1V).
VIN
VIN 2
1.25V
+
RUV1
UVLO 3
–
RUV2
3µA
UVLO
3742 F03
Figure 3. Undervoltage Lockout
3742fa
11
11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet LT3742.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT3740 | Synchronous Step-Down Controller |  Linear Technology |
| LT3741 | Step-Down Controller | Linear Technology |
| LT3741-1 | Step-Down Controller | Linear Technology |
| LT3742 | 2-Phase Step-Down Switching Controller | Linear Technology Corporation |
| 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 |