|
|
PDF LT3507A Data sheet ( Hoja de datos )
| Número de pieza | LT3507A | |
| Descripción | Triple Monolithic Step-Down Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT3507A (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
|
No Preview Available !
FEATURES
n Wide Input Range: 4V to 36V
n One 2.7A and Two 1.8A Output Switching
Regulators with Internal Power Switches
n Low Dropout Linear Regulator with External
Transistor
n Antiphase Switching Reduces Ripple
n Independent Run, Tracking/Soft-Start, and Power
Good Indicators Ease Supply Sequencing
n Uses Small Inductors and Ceramic Capacitors
n Adjustable, 250kHz to 2.5MHz Switching Frequency,
Synchronizable Over the Full Range
n User Programmable Overvoltage and Undervoltage
Lockouts
n Thermally Enhanced, 38-Lead TSSOP and
5mm × 7mm QFN Packages
APPLICATIONS
n Automotive
n Industrial Supplies
n Distributed Power Regulation
n DSP Power
LT3507A
Triple Monolithic Step-Down
Regulator with LDO
DESCRIPTION
The LT®3507A is a triple, current mode, DC/DC converter
with internal power switches and a low dropout regulator.
The switching converters are step-down converters capable
of generating one 2.7A output and two 1.8A outputs. All
three converters are synchronized to a single oscillator.
The 2.7A output runs with opposite phase to the other two
converters, reducing input ripple current. Each regulator
has independent shutdown and soft-start circuits, and
generates a power good signal when its output is in regu-
lation, easing power supply sequencing and interfacing
with microcontrollers and DSPs.
The switching frequency is set with a single resistor yielding
a range of 250kHz to 2.5MHz. The high switching frequency
allows the use of small inductors and capacitors resulting
in a very small triple output supply. The constant switching
frequency, combined with low impedance ceramic capaci-
tors, results in low, predictable output ripple. Frequency
foldback and thermal shutdown provide protection against
fault conditions. The LT3507A provides higher output cur-
rent than available with the LT3507.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V, 3.3V, 2.5V and 1.8V Step-Down Regulator
VIN
6V TO 36V
VOUT1
1.8V
2.7A
VOUT3
5V
1.8A
22µF
4.7µH
VIN1 VIN2 VIN3
BOOST1
BOOST2
0.22µF
SW1
18.7k
100µF
15k
25.5k
VOUT2
15µH
680pF
FB1
VC1
LT3507A
0.22µF BOOST3
SW3
53.6k
22µF
10.2k
25.5k 680pF
FB3
VC3
SW2
FB2
VC2
BIAS
DRIVE
RT/SYNC
107k GND
FB4
0.22µF
10µH
34.8k
680pF 25.5k 11k
24.3k
11.5k
VOUT2
3.3V
33µF 1.5A
2.2µF
VOUT4
2.5V
0.3A
fSW = 450kHz
3507A TA01a
Start-Up Waveforms—Coincident Tracking
1V/DIV
VOUT3
VOUT2
VOUT4
VOUT1
1ms/DIV
3507 TA01b
3507af
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT3507A
Efficiency vs Load Current,
Channel 1, VOUT = 1.8V
90 INDUCTOR: NIC NPIM74C4R7MTRF
fSW = 450kHz
80 VIN = 6V
VIN = 12V
70
VIN = 36V
60
50
40
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
IOUT (A)
3507A G01
BOOST Pin Current vs Switch
Current, Channels 1, 2 and 3
100
90
80
70
60 CHANNELS 2, 3
50
CHANNEL 1
40
30
20
10
0
0 0.5 1.0 1.5 2.0 2.5 3.0
ISW (A)
3507A G04
Frequency vs Temperature
0.5
0.0
–0.5
–1.0
–1.5
–2.0
–50 –30 –10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3507A G07
Efficiency vs Load Current,
Channels 2 and 3, VOUT = 3.3V
100
90 VIN = 6V
80 VIN = 12V
VIN = 36V
70
60
50
40
0
INDUCTOR: NIC NPIM74C8R2MTRF
fSW = 450kHz
0.3 0.6 0.9 1.2
IOUT (A)
1.5 1.8
3507A G02
VFB vs Temperature
805
804
803
802
801
800
799
798
797
796
795
–50 –30 –10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3507A G05
Frequency vs VFB (Foldback)
1200
1000
RT = 40.2k
TA = 25°C
800
600
400
200
0
0 0.2 0.4 0.6 0.8 1
VFB (V)
3507A G08
CShwaitncnheVlsCE1S,A2T
vs Switch
and 3
Current,
0.6 TA = 25°C
0.5
CHANNELS 2 AND 3
0.4
CHANNEL 1
0.3
0.2
0.1
0
0 0.5 1 1.5 2 2.5 3
ISW (A)
3507A G03
Frequency vs RT
2.5
2.0
1.5
1.0
0.5
0
0 20 40 60 80 100 120 140 160 180 200
RT (kΩ)
3507A G06
ITRK/SS vs Temperature
1.30
1.28
1.26
1.24
1.22
1.20
–50 –30 –10 30 50 70 90 110 130 150
TEMPERATURE (°C)
3507A G09
3507af
5
5 Page 
LT3507A
APPLICATIONS INFORMATION
fMAX2 is the frequency at which the maximum duty cycle
is exceeded. If there is sufficient charge on the BOOST
capacitor, the regulator will skip OFF periods to increase
the overall duty cycle at frequencies about fMAX2. It will
continue to regulate but with increased inductor current
and greatly increased output ripple.
Note that the restriction on the operating input voltage
refers to steady-state limits to keep the output in regula-
tion; the circuit will tolerate input voltage transients up to
the absolute maximum rating.
Switching Frequency
Once the upper and lower bounds for the switching
frequency are found from the duty cycle requirements,
the frequency may be set within those bounds. Lower
frequencies result in lower switching losses, but require
larger inductors and capacitors. The user must decide
the best trade-off.
The switching frequency is set by a resistor connected
from the RT/SYNC pin to ground, or by forcing a clock
signal into RT/SYNC. The LT3507A applies a voltage of
~1.25V across this resistor and uses the current to set
the oscillator speed. The switching frequency is given by
the following formula:
fSW
=
53.2
RT + 12.4
where fSW is in MHz and RT is in kΩ.
The formula will give a frequency value that is accurate to
within ±3%, for better accuracy use Table 1.
Table 1. RT for Common Frequencies
SWITCHING FREQUENCY (MHz)
0.25
0.5
0.75
1.0
1.25
1.5
1.75
2.0
2.25
2.5
RT (kΩ)
203
93.8
58.0
40.2
30.0
23.0
18.0
14.3
11.4
9.17
The frequency sync signal will support VH logic levels from
1.8V to 5V CMOS or TTL. The duty cycle is not important,
but it needs a minimum on time of 100ns and a minimum
off time of 100ns. If the sync circuit is to be powered from
one of the LT3507A outputs there may be start-up problems
if the driving gate is high impedance without a supply or
pulls high or low at some intermediate supply voltage.
The circuit shown in Figure 2 prevents these problems by
isolating the clock sync circuit until the clock is operating.
The Schottky diode should be a low leakage type such as
the BAS70 from On Semi or CMOD6263 from Central Semi.
RT should be set to provide a frequency within ±25% of
the final sync frequency.
VCC
CLOCK
SYNC
CLK
1k 470pF
BAS70
LT3507A
RT/SYNC SW1
RT
VOUT1
3507A F02
Figure 2. Clock Powered from LT3507A Output
Inductor Selection and Maximum Output Current
The current in the inductor is a triangle wave with an
average value equal to the load current. The peak switch
current is equal to the output current plus half the peak-
to-peak inductor ripple current. The LT3507A limits its
switch current in order to protect itself and the system
from overload faults. Therefore, the maximum output
current that the LT3507A will deliver depends on the
switch current limit, the inductor value and the input and
output voltages.
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
ΔIL
=
(1–
DC)
VOUT +
L•f
VF
where f is the switching frequency of the LT3507A and L
is the value of the inductor. The peak inductor and switch
current is:
ISWPK
= ILPK
= IOUT
+
ΔIL
2
3507af
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LT3507A.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT3507 | Triple Monolithic Step-Down Regulator |  Linear Technology |
| LT3507A | Triple Monolithic Step-Down 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 |