データシートサーチシステム
  Japanese  ▼
ALLDATASHEET.JP

X  

LM3475MF データシート(PDF) 10 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
部品番号 LM3475MF
部品情報  Hysteretic PFET Buck Controller
Download  14 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
メーカー  NSC [National Semiconductor (TI)]
ホームページ  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM3475MF データシート(HTML) 10 Page - National Semiconductor (TI)

Back Button LM3475MF Datasheet HTML 6Page - National Semiconductor (TI) LM3475MF Datasheet HTML 7Page - National Semiconductor (TI) LM3475MF Datasheet HTML 8Page - National Semiconductor (TI) LM3475MF Datasheet HTML 9Page - National Semiconductor (TI) LM3475MF Datasheet HTML 10Page - National Semiconductor (TI) LM3475MF Datasheet HTML 11Page - National Semiconductor (TI) LM3475MF Datasheet HTML 12Page - National Semiconductor (TI) LM3475MF Datasheet HTML 13Page - National Semiconductor (TI) LM3475MF Datasheet HTML 14Page - National Semiconductor (TI)  
Zoom Inzoom in Zoom Outzoom out
 10 / 14 page
background image
Design Information (Continued)
voltage regulated. The hysteretic control topology is well
suited to using ceramic output capacitors. However, ceramic
capacitors have a very low ESR, resulting in a 90˚ phase
shift of the output voltage ripple. This results in low operating
frequency and increased output ripple. To fix this problem a
low value resistor could be added in series with the ceramic
output capacitor. Although counter intuitive, this combination
of a ceramic capacitor and external series resistance provide
highly accurate control over the output voltage ripple. An-
other method is to add an external ramp at the FB pin as
shown in Figure 3. By proper selection of R1 and C2, the FB
pin sees faster voltage change than the output ripple can
cause. As a result, the switching frequency is higher while
the output ripple becomes lower. The switching frequency is
approximately:
Other types of capacitor, such as Sanyo POSCAP, OS-CON,
and Nichicon ’NA’ series are also recommended and may be
used without additional series resistance. For all practical
purposes, any type of output capacitor may be used with
proper circuit verification.
Capacitors with high ESL (equivalent series inductance) val-
ues should not be used. As shown in Figure 1, the output
ripple voltage contains a small step at both the high and low
peaks. This step is caused by and is directly proportional to
the output capacitor’s ESL. A large ESL, such as in an
electrolytic capacitor, can create a step large enough to
cause abnormal switching behavior.
INPUT CAPACITOR SELECTION
A bypass capacitor is required between V
IN and ground. It
must be placed near the source of the external PFET. The
input capacitor prevents large voltage transients at the input
and provides the instantaneous current when the PFET turns
on. The important parameters for the input capacitor are the
voltage rating and the RMS current rating. Follow the manu-
facturer’s recommended voltage de-rating. RMS current and
power dissipation (PD) can be calculated with the equations
below:
DIODE SELECTION
The catch diode provides the current path to the load during
the PFET off time. Therefore, the current rating of the diode
must be higher than the average current through the diode,
which be calculated as shown:
I
D_AVE =IOUT x(1−D)
The peak voltage across the catch diode is approximately
equal to the input voltage. Therefore, the diode’s peak re-
verse voltage rating should be greater than 1.3 times the
input voltage.
A Schottky diode is recommended, since a low forward
voltage drop will improve efficiency.
For high temperature applications, diode leakage current
may become significant and require a higher reverse voltage
rating to achieve acceptable performance.
P-CHANNEL MOSFET SELECTION
The PFET switch should be selected based on the maximum
Drain-Source voltage (VDS), Drain current rating (I
D), maxi-
mum Gate-Source voltage (VGS), on resistance (R
DSON),
and Gate capacitance. The voltage across the PFET when it
is turned off is equal to the sum of the input voltage and the
diode forward voltage. The VDS must be selected to provide
some margin beyond the sum of the input voltage and Vd.
Since the current flowing through the PFET is equal to the
current through the inductor, I
D must be rated higher than the
maximum I
PK. During switching, PGATE swings the PFET’s
gate from V
IN to ground. Therefore, A PFET must be se-
lected with a maximum VGS larger than V
IN. To insure that
the PFET turns on completely and quickly, refer to the
PGATE section.
20070120
FIGURE 3. External Ramp
www.national.com
10


同様の部品番号 - LM3475MF

メーカー部品番号データシート部品情報
logo
Texas Instruments
LM3475MF TI1-LM3475MF Datasheet
1Mb / 25P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3475MF/NOPB TI1-LM3475MF/NOPB Datasheet
1Mb / 25P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3475MFX/NOPB TI1-LM3475MFX/NOPB Datasheet
1Mb / 25P
[Old version datasheet]   Hysteretic PFET Buck Controller
More results

同様の説明 - LM3475MF

メーカー部品番号データシート部品情報
logo
National Semiconductor ...
LM3485 NSC-LM3485 Datasheet
369Kb / 15P
   Hysteretic PFET Buck Controller
logo
Texas Instruments
LM3485 TI-LM3485_15 Datasheet
1Mb / 24P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3485 TI1-LM3485_14 Datasheet
1,023Kb / 22P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3475 TI1-LM3475_14 Datasheet
1Mb / 21P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3485 TI1-LM3485_16 Datasheet
1Mb / 28P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3485MMX TI-LM3485MMX Datasheet
996Kb / 23P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3475 TI1-LM3475 Datasheet
1Mb / 25P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3485MM TI-LM3485MM Datasheet
1Mb / 23P
[Old version datasheet]   Hysteretic PFET Buck Controller
LM3485EVAL TI-LM3485EVAL Datasheet
1,023Kb / 22P
[Old version datasheet]   LM3485 Hysteretic PFET Buck Controller
LM3475 TI-LM3475_15 Datasheet
1Mb / 24P
[Old version datasheet]   LM3475 Hysteretic PFET Buck Controller
More results


Html Pages

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


データシート ダウンロード

Go To PDF Page


リンク URL




プライバシーポリシー
ALLDATASHEET.JP
ALLDATASHEETはお客様のビジネスに役立ちますか?  [ DONATE ] 

Alldatasheetは   |   広告   |   お問い合わせ   |   プライバシーポリシー   |   リンク交換   |   メーカーリスト
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