전자부품 데이터시트 검색엔진
  Korean  ▼
ALLDATASHEET.CO.KR

X  

LM2717MT-ADJ 데이터시트(PDF) 11 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
부품명 LM2717MT-ADJ
상세설명  Dual Step-Down DC/DC Converter
Download  16 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
제조업체  NSC [National Semiconductor (TI)]
홈페이지  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM2717MT-ADJ 데이터시트(HTML) 11 Page - National Semiconductor (TI)

Back Button LM2717MT-ADJ Datasheet HTML 7Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 8Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 9Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 10Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 11Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 12Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 13Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 14Page - National Semiconductor (TI) LM2717MT-ADJ Datasheet HTML 15Page - National Semiconductor (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 11 / 16 page
background image
Buck Operation (Continued)
the DC resistance. The inductance is related to the peak-to-
peak inductor ripple current, the input and the output volt-
ages (for 300kHz operation):
A higher value of ripple current reduces inductance, but
increases the conductance loss, core loss, and current
stress for the inductor and switch devices. It also requires a
bigger output capacitor for the same output voltage ripple
requirement. A reasonable value is setting the ripple current
to be 30% of the DC output current. Since the ripple current
increases with the input voltage, the maximum input voltage
is always used to determine the inductance. The DC resis-
tance of the inductor is a key parameter for the efficiency.
Lower DC resistance is available with a bigger winding area.
A good tradeoff between the efficiency and the core size is
letting the inductor copper loss equal 2% of the output
power.
OUTPUT CAPACITOR
The selection of C
OUT is driven by the maximum allowable
output voltage ripple. The output ripple in the constant fre-
quency, PWM mode is approximated by:
The ESR term usually plays the dominant role in determining
the voltage ripple. Low ESR ceramic, aluminum electrolytic,
or tantalum capacitors (such as MuRata MLCC, Taiyo Yuden
MLCC, Nichicon PL series, Sanyo OS-CON, Sprague 593D,
594D, AVX TPS, and CDE polymer aluminum) is recom-
mended. An aluminum electrolytic capacitor is not recom-
mended for temperatures below −25˚C since its ESR rises
dramatically at cold temperatures. Ceramic or tantalum ca-
pacitors have much better ESR specifications at cold tem-
perature and is preferred for low temperature applications.
BOOTSTRAP CAPACITOR
A 4.7nF ceramic capacitor or larger is recommended for the
bootstrap capacitor. For applications where the input voltage
is less than twice the output voltage a larger capacitor is
recommended, generally 0.1µF to 1µF to ensure plenty of
gate drive for the internal switches and a consistently low
R
DSON.
SOFT-START CAPACITOR (BOTH REGULATORS)
The LM2717-ADJ contains circuitry that can be used to limit
the inrush current on start-up of the DC/DC switching regu-
lators. This inrush current limiting circuitry serves as a soft-
start. The external SS pins are used to tailor the soft-start for
a specific application. A current (I
SS) charges the external
soft-start capacitor, C
SS. The soft-start time can be esti-
mated as:
T
SS =CSS*0.6V/ISS
When programming the soft-start time use the equation
given in the Soft-Start Capacitor section above. The soft-
start function is used simply to limit inrush current to the
device that could stress the input voltage supply. The soft-
start time described above is the time it takes for the current
limit to ramp to maximum value. When this function is used
the current limit starts at a low value and increases to
nominal at the set soft-start time. Under maximum load
conditions the output voltage may rise at the same rate as
the soft-start, however at light or no load conditions the
output voltage will rise much faster as the switch will not
need to conduct much current to charge the output capacitor.
SHUTDOWN OPERATION (BOTH REGULATORS)
The shutdown pins of the LM2717-ADJ are designed so that
they may be controlled using 1.8V or higher logic signals. If
the shutdown function is not to be used the pin may be left
open. The maximum voltage to the shutdown pin should not
exceed 7.5V. If the use of a higher voltage is desired due to
system or other constraints it may be used, however a 100k
or larger resistor is recommended between the applied volt-
age and the shutdown pin to protect the device.
SCHOTTKY DIODE
The breakdown voltage rating of D
1 and D2 is preferred to be
25% higher than the maximum input voltage. The current
rating for the diode should be equal to the maximum output
current for best reliability in most applications. In cases
where the input voltage is much greater than the output
voltage the average diode current is lower. In this case it is
possible to use a diode with a lower average current rating,
approximately (1-D)*I
OUT however the peak current rating
should be higher than the maximum load current.
LOOP COMPENSATION
The general purpose of loop compensation is to meet static
and dynamic performance requirements while maintaining
stability. Loop gain is what is usually checked to determine
small-signal performance. Loop gain is equal to the product
of control-output transfer function and the output-control
transfer function (the compensation network transfer func-
tion). The DC loop gain of the LM2717 is usually around
55dB to 60dB when loaded. Generally speaking it is a good
idea to have a loop gain slope that is -20dB /decade from a
very low frequency to well beyond the crossover frequency.
The crossover frequency should not exceed one-fifth of the
switching frequency, i.e. 60kHz in the case of 300kHz
switching frequency. The higher the bandwidth is, the faster
the load transient response speed will potentially be. How-
ever, if the duty cycle saturates during a load transient,
further increasing the small signal bandwidth will not help.
Since the control-output transfer function usually has very
limited low frequency gain, it is a good idea to place a pole in
the compensation at zero frequency, so that the low fre-
quency gain will be relatively large. A large DC gain means
high DC regulation accuracy (i.e. DC voltage changes little
with load or line variations). The rest of the compensation
scheme depends highly on the shape of the control-output
plot.
www.national.com
11


유사한 부품 번호 - LM2717MT-ADJ

제조업체부품명데이터시트상세설명
logo
National Semiconductor ...
LM2717MT-ADJ NSC-LM2717MT-ADJ Datasheet
395Kb / 16P
   Dual Step-Down DC/DC Converter
logo
Texas Instruments
LM2717MT-ADJ/NOPB TI-LM2717MT-ADJ/NOPB Datasheet
1Mb / 24P
[Old version datasheet]   LM2717-ADJ Dual Step-Down DC/DC Converter
More results

유사한 설명 - LM2717MT-ADJ

제조업체부품명데이터시트상세설명
logo
National Semiconductor ...
LM2717 NSC-LM2717 Datasheet
673Kb / 12P
   Dual Step-down DC/DC Converter
LM2717 NSC-LM2717_08 Datasheet
324Kb / 14P
   Dual Step-Down DC/DC Converter
LM2717-ADJ NSC-LM2717-ADJ_08 Datasheet
395Kb / 16P
   Dual Step-Down DC/DC Converter
logo
Texas Instruments
LM2717 TI-LM2717_15 Datasheet
957Kb / 17P
[Old version datasheet]   LM2717 Dual Step-Down DC/DC Converter
LM3370 TI1-LM3370_15 Datasheet
4Mb / 33P
[Old version datasheet]   Dual Synchronous Step-Down DC-DC Converter
logo
Rohm
BP5226-18 ROHM-BP5226-18 Datasheet
478Kb / 3P
   Step-down DC/DC converter
logo
Texas Instruments
LM3212 TI1-LM3212_16 Datasheet
981Kb / 25P
[Old version datasheet]   Step-Down DC-DC Converter
LM53625-Q1 TI1-LM53625-Q1_16 Datasheet
5Mb / 55P
[Old version datasheet]   Step-Down DC-DC Converter
TPS57140-Q1 TI1-TPS57140-Q1_16 Datasheet
2Mb / 53P
[Old version datasheet]   Step-Down DC-DC Converter
TPS54340-Q1 TI1-TPS54340-Q1_15 Datasheet
1Mb / 48P
[Old version datasheet]   Step-Down DC-DC Converter
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16


데이터시트 다운로드

Go To PDF Page


링크 URL




개인정보취급방침
ALLDATASHEET.CO.KR
ALLDATASHEET 가 귀하에 도움이 되셨나요?  [ DONATE ] 

Alldatasheet는?   |   광고문의   |   운영자에게 연락하기   |   개인정보취급방침   |   링크교환   |   제조사별 검색
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