công cụ tìm kiếm bảng dữ liệu linh kiện điện tử
  Vietnamese  ▼
ALLDATASHEET.VN

X  

LM2745MTC bảng dữ liệu(PDF) 9 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
tên linh kiện LM2745MTC
Giải thích chi tiết về linh kiện  Synchronous Buck Controller with Pre-bias Startup, and Optional Clock Synchronization
Download  23 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
nhà sản xuất  NSC [National Semiconductor (TI)]
Trang chủ  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM2745MTC bảng dữ liệu(HTML) 9 Page - National Semiconductor (TI)

Back Button LM2745MTC Datasheet HTML 5Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 6Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 7Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 8Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 9Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 10Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 11Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 12Page - National Semiconductor (TI) LM2745MTC Datasheet HTML 13Page - National Semiconductor (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 9 / 23 page
background image
Application Information (Continued)
is approximated by the curve FREQUENCY vs. FRE-
QUENCY ADJUST RESISTOR in the Typical Performance
Characteristics section.
When it is desired to synchronize the switching frequency
with an external clock source, the LM2745 has the unique
ability to synchronize from this external source within the
range of 250 kHz to 1 MHz. The external clock signal should
be AC coupled to the FREQ/SYNC pin as shown below in
Figure 1, where the R
FADJ is chosen so that the fixed fre-
quency is approximately within ±30% of the external syn-
chronizing clock frequency. An internal protection diode
clamps the low level of the synchronizing signal to approxi-
mately -0.5V. The internal clock sychronizes to the rising
edge of the external clock.
It is recommended to choose an AC coupling capacitance in
the range of 50 pF to 100 pF. Exceeding the recommended
capacitance may inject excessive energy through the inter-
nal clamping diode structure present on the FREQ/SYNC
pin.
The typical trip level of the synchronization pin is 1.5V. To
ensure proper synchronization and to avoid damaging the
IC, the peak-to-peak value (amplitude) should be between
2.5V and V
CC. The minimum width of this pulse must be
greater than 100 ns, and it’s maximum width must be 100ns
less than the period of the switching cycle.
The external clock synchronization process begins once the
LM2745 is enabled and an external clock signal is detected.
During the external clock synchronization process the inter-
nal clock initially switches at approximately 1.5 MHz and
decreases until it has matched the external clock’s fre-
quency. The lock-in period is approximately 30 µs if the
external clock is switching at 1 MHz, and about 100 µs if the
external clock is at 200 kHz. When there is no clock signal
present, the LM2745 enters into fixed-frequency mode and
begins switching at the frequency set by the R
FADJ resistor.
If the external clock signal is removed after frequency syn-
chronization, the LM2745 will enter fixed-frequency mode
within two clock cycles. If the external clock is removed
within the 30 µs lock-in period, the LM2745 will re-enter
fixed-frequency mode within two internal clock cycles after
the lock-in period.
OUTPUT PRE-BIAS STARTUP
If there is a pre-biased load on the output of the LM2745/8
during startup, the IC will disable switching of the low-side
MOSFET and monitor the SW node voltage during the off-
time of the high-side MOSFET. There is no load current
sensing while in pre-bias mode because the low-side MOS-
FET never turns on. The IC will remain in this pre-bias mode
until it sees the SW node stays below 0V during the entire
high-side MOSFET’s off-time. Once it is determined that the
SW node remained below 0V during the high-side off-time,
the low-side MOSFET begins switching during the next
switching cycle. Figure 2 shows the SW node, HG, and LG
signals during pre-bias startup. The pre-biased output volt-
age should not exceed V
CC +VGS of the external High-Side
MOSFET to ensure that the High-Side MOSFET will be able
to switch during startup.
TRACKING A VOLTAGE LEVEL
The LM2745/8 can track the output of a master power supply
during soft-start by connecting a resistor divider to the SS/
TRACK pin. In this way, the output voltage slew rate of the
LM2745/8 will be controlled by the master supply for loads
that require precise sequencing. When the tracking function
is used no soft-start capacitor should be connected to the
SS/TRACK pin. However in all other cases, a C
SS value of at
least 1 nF between the soft-start pin and ground should be
used.
One way to use the tracking feature is to design the tracking
resistor divider so that the master supply’s output voltage
(V
OUT1) and the LM2745/8’s output voltage (represented
symbolically in Figure 3 as V
OUT2, i.e. without explicitly
showing the power components) both rise together and
20137489
FIGURE 1. AC Coupled Clock
20137491
FIGURE 2. Output Pre-Bias Mode Waveforms
20137407
FIGURE 3. Tracking Circuit
www.national.com
9


Số phần tương tự - LM2745MTC

nhà sản xuấttên linh kiệnbảng dữ liệuGiải thích chi tiết về linh kiện
logo
Texas Instruments
LM2745MTC TI-LM2745MTC Datasheet
1Mb / 37P
[Old version datasheet]   LM2745 / LM2748 Synchronous Buck Controller with Pre-Bias Startup, and Optional Clock
LM2745MTC/NOPB TI1-LM2745MTC/NOPB Datasheet
1Mb / 37P
[Old version datasheet]   LM2745 / LM2748 Synchronous Buck Controller with Pre-Bias Startup
LM2745MTCX TI-LM2745MTCX Datasheet
1Mb / 37P
[Old version datasheet]   LM2745 / LM2748 Synchronous Buck Controller with Pre-Bias Startup, and Optional Clock
LM2745MTCX/NOPB TI1-LM2745MTCX/NOPB Datasheet
1Mb / 37P
[Old version datasheet]   LM2745 / LM2748 Synchronous Buck Controller with Pre-Bias Startup
More results

Mô tả tương tự - LM2745MTC

nhà sản xuấttên linh kiệnbảng dữ liệuGiải thích chi tiết về linh kiện
logo
Texas Instruments
LM2747 TI-LM2747_15 Datasheet
1Mb / 38P
[Old version datasheet]   Synchronous Buck Controller with Pre-Bias Startup, and Optional Clock Synchronization
logo
National Semiconductor ...
LM2747 NSC-LM2747 Datasheet
1,009Kb / 23P
   Synchronous Buck Controller with Pre-bias Startup, and Optional Clock Synchronization
logo
Texas Instruments
LM2745MTCX TI-LM2745MTCX Datasheet
1Mb / 37P
[Old version datasheet]   LM2745 / LM2748 Synchronous Buck Controller with Pre-Bias Startup, and Optional Clock
LM2748MTC TI1-LM2748MTC Datasheet
1Mb / 37P
[Old version datasheet]   LM2745 / LM2748 Synchronous Buck Controller with Pre-Bias Startup
logo
International Rectifier
IR3621 IRF-IR3621 Datasheet
375Kb / 29P
   2-PHASE / DUAL SYNCHRONOUS PWM CONTROLLER WITH OSCILLATOR SYNCHRONIZATION AND PRE-BIAS STARTUP
logo
Delta Electronics, Inc.
DNL DELTA-DNL Datasheet
936Kb / 15P
   Pre-bias startup
DNT12SIP05 DELTA-DNT12SIP05 Datasheet
716Kb / 13P
   Pre-bias startup
logo
Texas Instruments
TPS40195RGYTG4 TI-TPS40195RGYTG4 Datasheet
1Mb / 44P
[Old version datasheet]   4.5-V TO 20-V SYNCHRONOUS BUCK CONTROLLER WITH SYNCHRONIZATION AND
TPS40195 TI-TPS40195 Datasheet
665Kb / 39P
[Old version datasheet]   4.5-V TO 20-V SYNCHRONOUS BUCK CONTROLLER WITH SYNCHRONIZATION AND POWER GOOD
logo
National Semiconductor ...
LM20136 NSC-LM20136 Datasheet
543Kb / 22P
   6A, Synchronous Buck Regulator with Input Synchronization
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23


bảng dữ liệu tải về

Go To PDF Page


Link URL




Chính sách bảo mật
ALLDATASHEET.VN
Cho đến nay ALLDATASHEET có giúp ích cho doanh nghiệp của bạn hay không?  [ DONATE ] 

Alldatasheet là   |   Quảng cáo   |   Liên lạc với chúng tôi   |   Chính sách bảo mật   |   Trao đổi link   |   Tìm kiếm theo nhà sản xuất
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com