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PDF LT3504 Data sheet ( Hoja de datos )
| Número de pieza | LT3504 | |
| Descripción | Quad 40V/1A Step-Down Switching Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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Features
n Wide Input Range: 3.2V to 40V
n Four 1A Outputs
n 100% Duty Cycle Operation
n Resistor-Programmed Constant Frequency
n Short-Circuit Robust
n Wide SYNC Range: 350kHz to 2.2MHz
n Anti-Phase Switching Reduces Ripple
n 800mV FB Voltage
n Independent Run/Soft-Start Pins
n Shutdown with UVLO
n Internal Compensation
n Thermal Shutdown
n Tiny 28-Lead (4mm × 5mm) Thermally Enhanced
QFN Package
Applications
n Automotive Battery Regulation
n Industrial Control Supplies
n Wall Transformer Regulation
n Distributed Supply Regulation
LT3504
Quad 40V/1A Step-Down
Switching Regulator with
100% Duty Cycle Operation
Description
The LT®3504 consists of four 1A output current buck
regulators. The LT3504 has a wide operating input range
of 3.2V to 40V. An on-chip boost regulator allows each
channel to operate up to 100% duty cycle and eliminates
the need for four external charge pump circuits. The LT3504
is designed to minimize external component count and
results in a simple and small application circuit.
The LT3504 operates robustly in fault conditions. Cycle-
by-cycle peak current limit and catch diode current limit
sensing protect the part during overload conditions. Ther-
mal shutdown protects the power switches at elevated
temperatures. Soft-start helps keep the peak inductor
current under control during startup.
The LT3504 also features output voltage tracking and
sequencing, programmable frequency, programmable
undervoltage lockout, and a power good pin to indicate
when all outputs are in regulation.
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.
Typical Application
Quad Buck Regulator in 4 × 5 QFN
VIN
5.4V to 20V
TRANSIENT TO 40V
1µF
1µF
10µH
1µF
50nF
SKY
LT3504
SW5
EN/UVLO
VIN
VIN
VIN
VIN
RUN/SS1
RUN/SS2
RUN/SS3
RUN/SS4
RT/SYNC
18.2k
GND
SW4
DA4
FB4
SW3
DA3
FB3
SW2
DA2
FB2
SW1
DA1
FB1
fSW = 1MHz
10µH
52.3k
5V/1A
10µF
6.8µH
10k
31.6k
3.3V/1A
10µF
4.7µH
10k
22.1k
2.5V/1A
22µF
3.3µH
10k
24.9k
20k
1.8V/1A
22µF
3504 TA01a
For more information www.linear.com/LT3504
LT3504 Start-Up and Shutdown
Waveform.
from 0V Up
VtoIN8(VToapndTrTahcee)n
Is Ramped
Back Down
to 0V. The Other Four Traces Are the
Output Voltages of All Four Channels
5V CHANNEL BEGINS
100% DC OPERATION
3.3V CHANNEL BEGINS
100% DC OPERATION
VIN 1V/DIV
CH4 1V/DIV
UVLO = ~2.9V
PARTS SHUTS
OFF
CH3 1V/DIV
CH2 1V/DIV
CH1 1V/DIV
100ms/DIV
3504 TA01b
3504fa
1
1 page  
LT3504
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
Input Voltage Undervoltage
Lockout
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3504 G10
VIN Pin Current
10
9
8
7
6
5
4
3
2
1
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VEN/UVLO (V)
3504 G11
RUN/SS vs FB Voltage
900
800
700
600
500
400
300
200
100
0
0 200 400 600 800 1000 1200
RUN/SS VOLTAGE (mV)
3504 G13
Switch Voltage Drop
600
500
400
300
200
100
0
0 200 400 600 800 1000
SWITCH CURRENT (mA)
3504 G16
Soft Start Current
0
–0.2
–0.4
–0.6
–0.8
–1.0
–1.2
–1.4
–1.6
–1.8
–2.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3504 G14
Switch Voltage Drop,
ISW = 500mA
320
300
280
260
240
220
200
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3504 G17
For more information www.linear.com/LT3504
Input Quiescent Current
vs Input Voltage
40
35
30
25
20
15
10
5 ALL SS = 2V
ALL SS = 0V
0
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
3504 G12
Switching Frequency
vs Temperature
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3504 G15
Switch and Diode Current Limit
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
3504 G18
3504fa
5
5 Page 
LT3504
applications information
Frequency Selection
The maximum frequency that the LT3504 can be pro-
grammed to is 2.5MHz. The minimum frequency is 250kHz.
The switching frequency can be programmed in two ways.
The first method is by tying a 1% resistor (RT) from the
RT/SYNC pin to ground. Table 1 can be used to select the
value of RT. The second method is to synchronize (sync)
the internal oscillator to an external clock. The external
clock must have a minimum amplitude from 0V to 1.6V
and a minimum pulse-width of 50ns.
Table 1. RT/SYNC Pin Resistance to Program Oscillator
Frequency
FREQUENCY (MHz)
RT/SYNC PIN RESISTANCE (kΩ)
0.20 140
0.3 82.5
0.4 56.2
0.5 43.2
0.6 34.8
0.7 28.0
0.8 23.7
0.9 20.5
1.0 18.2
1.1 16.9
1.2 14.7
1.3 13.0
1.4 11.5
1.5 10.7
1.6 9.76
1.7 8.66
1.8 8.06
1.9 7.32
2.0 6.81
2.1 6.34
2.2 6.04
2.3 5.62
2.4 5.36
2.5 4.99
In certain applications, the LT3504 may be required to be
alive and switching for a period of time before it begins
to receive a sync signal. If the sync signal is in a high
impedance state when it is inactive then the solution is to
simply tie an RT resistor from the RT/SYNC pin to ground
(Figure 2). The sync signal should be capable of driving the
RT resistor. If the sync signal is in a low impedance state
or an unknown state when it is inactive, then the solution
is to tie the RT resistor from the RT/SYNC pin to ground
and then to drive the RT/SYNC pin with the sync signal
through a 1nF capacitor as shown in Figure 3.
PORT
LT3504
RT/SYNC
RT
GND
3504 F02
Figure 2. Driving the RT/SYNC Pin From
a Port That Is in a High Impedance State
When it Is Inactive
PORT
1nF LT3504
RT/SYNC
RT
GND
3504 F03
Figure 3. Driving the RT/SYNC Pin from
a Port That Is in a Low Impedance State
When it Is Inactive
BOOST Regulator and SKY Pin Considerations
The on-chip boost regulator generates the SKY voltage
to be 4.85V above VIN. The SKY voltage is the source of
drive current for the buck regulators which is used to fully
saturate the power switch. The boost regulator requires
two external components: an inductor and a capacitor.
A good first choice for an inductor is given by:
L
=
20.5µH
f
where f is in MHz.
Thus, for a 250kHz programmed switching frequency,
a good first choice for an inductor value is 82µH. For a
2.5MHz programmed switching frequency, a good first
For more information www.linear.com/LT3504
3504fa
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT3504.PDF ] | |
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