Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

AN701 Datasheet(PDF) 5 Page - Vishay Siliconix

Part No. AN701
Description  reduce the size of energy storage components
Download  19 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  VISHAY [Vishay Siliconix]
Homepage  http://www.vishay.com
Logo 

AN701 Datasheet(HTML) 5 Page - Vishay Siliconix

 
Zoom Inzoom in Zoom Outzoom out
 5 / 19 page
background image
AN701
Vishay Siliconix
Document Number: 70575
16-Jan-01
www.vishay.com
5
Figure 7 Oscillator
I1
C1
VREF
C2
I2
Q2
B1
B2
B3
SW1
Q1
CT
RT
U1
DQ
Q
CLK
SYNC
Figure 8 Oscillator Synchronization
+VIN
SHD
VREF
NI
FB
COMP
SS
VCC
Sense
Out
–VIN
SYNC
COSC
ROSC
Si9114A
14
13
12
11
10
9
8
1
2
3
4
5
6
7
Si9114A
14
13
12
11
10
9
8
1
2
3
4
5
6
7
Si9114A
14
13
12
11
10
9
8
1
2
3
4
5
6
7
Rt
Ct
IC1
IC2
IC3
+VIN
SHD
VREF
NI
FB
COMP
SS
VCC
Sense
Out
–VIN
SYNC
COSC
ROSC
+VIN
SHD
VREF
NI
FB
COMP
SS
VCC
Sense
Out
–VIN
SYNC
COSC
ROSC
VCC
R1
120 k
CVCC
1
mF
CT
–VIN
Rt
Ct
RT
68 k
SW1
SW1 Closed = Frequency High
SW1 Open = Frequency Low
Figure 9 Frequency Shifting Using Rt Current Change
D1
In certain circumstances, such as current limiting, it may be
desirable to change the frequency of the converter for a period
of time to overcome current tails (see Figure 16 for further
explanation). With the Si9114A, this is easily done by adding
or subtracting some current into the RT terminal:
S The charging current in CT is set by 8
RT.
S The voltage at the RT terminal is 4 V, as supplied by an
internal emitter follower from the reference.
The frequency can be changed easily by supplying some of
the current into RT from the VCC rail, thus “starving” the
internal current source, and slowing the frequency down.
The current in RT is set by V = IR where V = 4 V and R = RT.
Using a diode, and some type of switch, the frequency can be
easily changed: when SW1 is closed, D1 is reverse biased, and
has no effect on RT. When SW1 is open, current flows through
R1 and D1 into RT and removes some of the current supplied
by the internal emitter follower.
PIN 10 SYNCHRONIZATION
The SYNC input allows operation from a master clock as the
connection is made after the divide-by-two. As a result,
synchronization in both frequency and phase is possible. This
unique feature is important to systems designers who use
multiple
converters,
where
noise
caused
by
an
unsynchronized “beating” effect is present and causes difficult
EMI/EMC problems. If an external clock is used, duty cycles of
>50% are possible due to the position of the SYNC pin , after
the divide-by-two. Where >50% conduction is used, core reset
must be allowed, in order to prevent core saturation.
Synchronization is in master/slave mode, with one device (the
“master”) setting the switching frequency and others (the
“slaves”) with disabled oscillators locked to it. Alternatively, all
devices can be clocked using a master oscillator.
During slave mode, the unused CT pin should be connected to
ground, and the RT to VCC.


Html Pages

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


Datasheet Download




Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
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