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PDF SI9117 Data sheet ( Hoja de datos )
| Número de pieza | SI9117 | |
| Descripción | High-Frequency Converter | |
| Fabricantes | Vishay | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SI9117 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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Si9117
Vishay Siliconix
High-Frequency Converter for Telecom Applications
FEATURES
D On-board high-voltage, 1-W Switching FET
D Switching Frequencies of Up to 1 MHz
D Synchronization Capability
D Easily Compensated Current-Mode Operation
DESCRIPTION
The Si9117 high-efficiency converter for telecom systems
running off 48 V is ideal for emerging applications such as
interactive video (IV) set-top boxes and microcell base
stations, such as those used for Personal Communications
Systems (PCS). IV set-top boxes and microcell base stations
typically require less than 15 W of power and have access to
the analog telephone line power. Both IV set-top boxes and
microcell base stations process extremely low-level,
modulated analog signals (on the order of mVs), making the
frequency and energy content of radiated and conducted
noise a major issue. These application circuits are also
constrained in terms of available board space and place a
premium on minimal footprint.
The combination of an on-board, high-voltage, 1-W switch and
a PWM IC with operational input voltage of 200 V allows
operation off of the analog telephone line, even with the worst
case battery voltage and ringing voltage. Once the converter
has started up, a simple bootstrap circuit can provide power to
the IC by raising the source voltage of the n-channel, depletion
mode, start-up FET above its gate voltage of 9.2 V. This
technique lowers system costs, reduces the area required for
circuit implementation, and minimizes circuit power
consumption.
APPLICATIONS CIRCUIT
VIN
D Operates with Input Voltages Up to 200 V
D 1.8-MHz Error Amplifier
D Soft-Start
D Latched SHUTDOWN
Processing high-frequency, modulated analog signals for
video or RF requires receivers with sensitivities in the range of
0.5 to 25 mV. At these levels, noise generated by switchmode
power conversion can impair the signal recovery process.
Controlling radiated noise is a matter of proper layout and
shielding. Controlling conducted noise is a matter of limiting its
energy and isolating the conducted energy’s fundamental and
harmonic frequencies to bands which will not affect the
frequencies of interest. The high-frequency, synchronized
switching of the Si9117 enables this design requirement. First,
for a given output current, high-frequency switching attenuates
output ripple, minimizing conducted energy. Second,
synchronizing the high switching frequency to an external
frequency allows the fundamental and its harmonics to be
moved out of range of the frequency bands of interest. An
additional benefit of high-frequency switching is reduced size
and cost of the inductor and the output filter capacitance.
In addition to these mandatory design considerations, the
Si9117 is easy to design with and compensate, and takes a
minimum of board area to implement: an important benefit in
high-volume/small-package applications such as set-top
boxes and microcell base stations.
The Si9117 is available in both standard and lead (Pb)-free
packages.
+
VOUT
1 16
2 15
3 14
SYNC 4 Si9117 13
5 12
6 11
7 10
89
SHUTDOWN
NC
Document Number: 70027
S-40750—Rev. E, 19-Apr-04
www.vishay.com
1
Free Datasheet http://www.datasheet-pdf.com/
1 page  
TYPICAL CHARACTERISTICS
Error Amp Gain and Phase
100 −20
80 −40
60 Gain
40
Phase
20
0
−60
−80
−100
−120
−20
0.1
1 10 100
f − Frequency (kHz)
−140
1000 4000
Oscillator Frequency vs. Temperature
215 1050
f = 1 MHz
210
1025
205
f = 200 kHz
200
1000
975
195
−50
−25
0
950
25 50 75 100
TJ − Temperature (_C)
Si9117
Vishay Siliconix
Reference Voltage vs. Temperature
4020
4010
4000
3990
3980
3970
3960
−50
−25
0
25 50 75 100
Document Number: 70027
S-40750—Rev. E, 19-Apr-04
www.vishay.com
5
Free Datasheet http://www.datasheet-pdf.com/
5 Page 
1000
COSC = 47 pF
100 pF
150 pF
200 pF
100
10
10
100
ROSC − Oscillator Resistance (kHz)
1000
FIGURE 6. Oscillator Frequency Selection
Si9117
Vishay Siliconix
−VIN
VCC
R1
120 k
Rt D1
CVCC
1 mF
Ct SW1
RT
CT 68 k
SW1 Closed = Frequency High
SW1 Open = Frequency Low
FIGURE 7. Frequency Shifting Using Rt Current Change
Ct Rt Si9117
1 SS COMP 16
2 ROSC
FB 15
3 COSC
NI 14
4 SYNC VREF 13
5 V−
SD 12
6 VCC
7 ISENSE
8S
V+ 11
NC 10
D9
IC1
Si9117
1 SS COMP 16
2 ROSC
FB 15
3 COSC
NI 14
4 SYNC VREF 13
5 V−
SD 12
6 VCC
7 ISENSE
8S
V+ 11
NC 10
D9
IC2
FIGURE 8. Oscillator Synchronization
Si9117
1 SS COMP 16
2 ROSC
FB 15
3 COSC
NI 14
4 SYNC VREF 13
5 V−
SD 12
6 VCC
7 ISENSE
8S
V+ 11
NC 10
D9
IC3
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.
Synchronization
The SYNC input allows operation from a master clock as the
connection is made after the divide-by-two. As a result,
Document Number: 70027
S-40750—Rev. E, 19-Apr-04
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. (See
Figure 8.)
www.vishay.com
11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet SI9117.PDF ] | |
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