|
|
PDF LTC3776 Data sheet ( Hoja de datos )
| Número de pieza | LTC3776 | |
| Descripción | No RSENSE Synchronous Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC3776 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
|
No Preview Available !
FEATURES
■ No Current Sense Resistors Required
■ Out-of-Phase Controllers Reduce Required
Input Capacitance
■ VOUT2 Tracks 1/2 VREF
■ Symmetrical Source/Sink Output Current
Capability (VOUT2)
■ Spread Spectrum Operation (When Enabled)
■ Wide VIN Range: 2.75V to 9.8V
■ Constant Frequency Current Mode Operation
■ 0.6V ±1.5% Voltage Reference (VOUT1)
■ Low Dropout Operation: 100% Duty Cycle
■ True PLL for Frequency Locking or Adjustment
■ Internal Soft-Start Circuitry
■ Power Good Output Voltage Monitor
■ Output Overvoltage Protection
■ Micropower Shutdown: IQ = 9µA
■ Tiny Low Profile (4mm × 4mm) QFN and Narrow
SSOP Packages
U
APPLICATIO S
■ DDR, DDR II and QDR Memory
www■.DaStaSSTheLe,t4HUS.cToLmTermination Supplies
■ Servers, RAID Systems
■ Distributed DC Power Systems
LTC3776
Dual 2-Phase, No RSENSETM,
Synchronous Controller for
DDR/QDR Memory Termination
DESCRIPTIO
The LTC®3776 is a 2-phase dual output synchronous step-
down switching regulator controller for DDR/QDR memory
termination applications. The second controller regulates
its output voltage to 1/2 VREF while providing symmetrical
source and sink output current capability.
The No RSENSE constant frequency current mode architec-
ture eliminates the need for sense resistors and improves
efficiency. Power loss and noise due to the ESR of the
input capacitance are minimized by operating the two
controllers out of phase.
The switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and ca-
pacitors. For noise sensitive applications, the LTC3776
switching frequency can be externally synchronized from
250kHz to 850kHz, or can be enabled for spread spectrum
operation. Forced continuous operation reduces noise and
RF interference. Soft-start for VOUT1 is provided internally
and can be extended using an external capacitor.
The LTC3776 is available in the tiny thermally enhanced
(4mm × 4mm) QFN package or 24-lead SSOP narrow
package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark of Linear Technology Corporation. No RSENSE is a trademark of
Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258,
6304066, 6611131, 6498466, patent pending on Spread Spectrum.
TYPICAL APPLICATIO
High Efficiency, 2-Phase, DDR Memory (VDDQ and VTT) Supplies
VIN
3.3V
VIN
SENSE1+ SENSE2+
10µF
×2
1.5µH
TG1 TG2
SW1 SW2
LTC3776
BG1 BG2
1.5µH
PGND
PGND
(VDDQ)VOUT1
2.5V
4A
187k
47µF
470pF
59k
VREF
VFB1
VFB2
ITH1 ITH2
SGND
15k
2200pF
6.2k
VOUT2 (VTT)
1.25V
±4A
47µF
3776 TA01a
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
10
FIGURE 14 CIRCUIT
CHANNEL 2 (VIN = 3.3V)
CHANNEL 1 (VIN = 5V)
CHANNEL 1 (VIN = 3.3V)
CHANNEL 2 (VIN = 5V)
100 1000
LOAD CURRENT (mA)
10000
3776 TA01b
3776f
1
1 page  
LTC3776
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Maximum Current Sense Voltage
vs ITH2 Pin Voltage (CH2)
100
80
60
40
20
0
–20
–40
–60
–80
–100
0
1.0 1.5
ITH2 VOLTAGE (V)
2.0
3776 G08
Shutdown (RUN) Threshold
vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
www.Dat0aSheet4U.com
–60 –40 –20 0 20 40 60 80 100
TEMPERATURE (°C)
3736 G11
Maximum Current Sense
Threshold (CH2) vs Temperature
150 IPRG2 = FLOAT
145
140
135
130
125
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3776 G14
Regulated Feedback Voltage
(CH2) vs Temperature
1.2625
VREF = 2.500V
1.2600
1.2575
1.2550
1.2525
1.2500
1.2475
1.2450
1.2425
1.2400
1.2375
–60 –40 –20 0 20 40 60 80 100
TEMPERATURE (°C)
3776 G09
RUN/SS Pull-Up Current
vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3736 G12
Oscillator Frequency
vs Temperature
10
8
6
4
2
0
–2
–4
–6
–8
–10
–60 –40 –20 0 20 40 60 80 100
TEMPERATURE (°C)
3736 G15
Regulated Feedback Voltage
(CH1) vs Temperature
0.612
0.608
0.604
0.600
0.596
0.592
0.588
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3776 G10
Maximum Current Sense Threshold
(CH1) vs Temperature
135 IPRG1 = FLOAT
130
125
120
115
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3736 G13
Undervoltage Lockout Threshold
vs Temperature
2.50
2.45
VIN RISING
2.40
2.35
2.30
VIN FALLING
2.25
2.20
2.15
2.10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
3736 G16
3776f
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
phase detector adjusts the voltage on the PLLLPF pin to
align the turn-on of controller 1’s external P-channel
MOSFET to the rising edge of the synchronizing signal.
Thus, the turn-on of controller 2’s external P-channel
MOSFET is 180 degrees out of phase with the rising edge
of the external clock source.
The typical capture range of the LTC3776’s phase-locked
loop is from approximately 200kHz to 1MHz, with a
guarantee over all process variations and temperature to
be between 250kHz and 850kHz. In other words, the
LTC3776’s PLL is guaranteed to lock to an external clock
source whose frequency is between 250kHz and 850kHz.
Alternatively, the SYNC/SSEN pin may be tied to VIN to
–10
RBW = 3kHz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
0
6 12 18 24 30
FREQUENCY (MHz)
37361 F01a
Figure 1a. Output Noise Spectrum of Conventional Buck
www.DSatwaiStchheient4gUC.coonmverter (LTC3776 with Spread Spectrum
Disabled) Showing Fundamental and Harmonic Frequencies
–10
RBW = 1kHz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
0
6 12 18
FREQUENCY (MHz)
24 30
37361 F01c
Figure 1c. Output Noise Spectrum of the LTC3776 Spread
Spectrum Buck Switching Converter. Note the Reduction in
Fundamental and Harmonic Peak Spectral Amplitude
Compared to Figure 1a.
LTC3776
enable spread spectrum operation (see Spread Spectrum
Operation section).
Spread Spectrum Operation
Switching regulators can be particularly troublesome in
applications where electromagnetic interference (EMI) is
a concern. Switching regulators operate on a cycle-by-
cycle basis to transfer power to an output. In most cases,
the frequency of operation is either fixed or is a constant
based on the output load. This method of conversion
creates large components of noise at the frequency of
operation (fundamental) and multiples of the operating
frequency (harmonics). Figures 1a and 1b depict the
–10
RBW = 30Hz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
410
450 490 530 570 610
FREQUENCY (kHz)
37361 F01b
Figure 1b. Zoom-In of Fundamental Frequency of Conventional
Buck Switching Converter
–10
RBW = 30Hz
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
410
450 490 530 570 610
FREQUENCY (kHz)
37361 F01d
Figure 1d. Zoom-In of Fundamental Frequency of the
LTC3776 Spread Spectrum Switching Converter. Note the
>20dB Reduction in Peak Amplitude and Spreading of the
Frequency Spectrum (Between Approximately 450kHz and
580kHz) Compared to Figure 1b.
3776f
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3776.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC3770 | Synchronous Controller | Linear Technology |
| LTC3772 | Micropower No RSENSE Constant Frequency Step-Down DC/DC Controller | Linear Technology |
| LTC3772B | Micropower No RSENSE Constant Frequency Step-Down DC/DC Controller | Linear Technology |
| LTC3773 | Triple Output Synchronous 3-Phase DC/DC Controller | 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 |