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PDF AN727 Data sheet ( Hoja de datos )
| Número de pieza | AN727 | |
| Descripción | High-Frequency / High-Efficiency Buck Converter Design For Multi-Cell Battery Configured Systems | |
| Fabricantes | Vishay Siliconix | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AN727 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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AN727
Vishay Siliconix
High-Frequency, High-Efficiency Buck Converter Design For
Multi-Cell Battery Configured Systems Using Si9167
Nitin Kalje
INTRODUCTION
The Si9167 is a high-frequency synchronous dc-to-dc
switching buck regulator, with an operating range suitable for
two-cell Li+ battery-powered applications. Capable of
operation up to 2 MHz, the Si9167 can be used to supply
power amplifiers and to power up baseband circuits in satellite
phones. Its high operating frequency reduces the size of
inductor and capacitor components, while its low
on-resistance internal driver ensures maximum power
conversion efficiency. Additional features include an
integrated input undervoltage lockout, power on reset,
integrated soft start, light load pulse skipping mode selection,
synchronization, clock output for master-slave configuration of
multiple regulators, uncommitted power-good comparator,
and over temperature protection. An output power in excess of
2 W at 3.6 VO is possible in 0.3 square inches.
TYPICAL APPLICATION CIRCUIT
+VIN 1
5 - 10 V
2
PGND
C1
10 mF
16 V
C1
0.1 mF
ENABLE/DISABLE
PWM/PSM
Si9167
1
SD
20
COIL
2 19
PWM/PSM COIL
R9*
51 kW
3
VIN
4
VIN
5
POK
PGND
COIL
PGND
18
17
16
6
SYNC
15
POKIN
1.3 V
C3
0.1 mF
7
CLK
8
GND
9
VREF
10
FB
VO
VDD
ROSC
COMP
14
13
12
11
STAR GND CON
* Optional
R3
8.2 kW
C5
1000 pF
R1*
51 W
L1
4.7 mH
IHLP2525
D1
R2
75 kW
C4
56 pF
C6
0.1 mF
R4
200 W
C7
330 pF
FIGURE 1. Typical Application Circuit—Buck
C1
10 mF
16 V
R5
22 kW
R6
12.4 kW
3.6 V @ 600 mA
7
VOUT
C9
0.1 mF
8
PGND
R7
105 kW
R8
64 kW
Document Number: 70959
07-Jul-99
www.vishay.com S FaxBack 408-970-5600
1
1 page  
AN727
Vishay Siliconix
Where
VINMAX = Maximum input voltage (V)
VOUT = Output Voltage (V)
VDSQP = Voltage drop across the main switch (V)
DI = Max ripple current allowed for acceptable ripple (A)
dMIN= Duty ratio at VINMAX.
VR_DROP = Resistive drop through inductor and PCB traces (V)
IOUT = Rated output current (A)
RL = Equivalent Series Resistance (W)
RTRACE = Combined resistance of positive and negative output
traces (W)
Fsw = Oscillator Frequency (Hz)
Refer to Figure 7 when deciding the inductance and frequency.
The frequency VS inductance plot assumes a 10-mF ceramic
multilayer chip capacitor with a 20-mW maximum ESR and
10-mVp-p output ripple.
FSW vs. Inductance
16
14
12
10
8
6
4
2
0
300 500 700 900 1100 1300 1500 1700 1900
Fsw (kHz)
FIGURE 7. Inductor Value Selection for 10-mF Ceramic
Output Capacitor
Output Voltage
The divider resistor pair, R5 and R6 in Figure 1 determine the
output regulation point. Since R5 is part of the compensation
network, it is strongly recommended that R6 be adjusted in
order to change the regulation voltage without affecting the
loop gain. With fixed R5, R6 can be easily calculated by (3) for
the desired output voltage setting.
R6
+
R5
VOUT
VREF
*
1
The typical value for VREF is 1.3 V.
(3)
Power_Good Comparator
The inverting input is internally connected to the reference
voltage of 1.3 V (see functional block diagram, Figure 2). This
uncommitted comparator, with about 50 mV hysteresis, is
intended to be used to sense the output voltage and raise a
high flag once the output voltage Vout reaches its regulation
limit. The 50-mV hysteresis at the comparator input is provided
while output is transitional from high to low. The output is
capable of sourcing 2 mA and sinking 1 mA current. The source
current can be increased up to 1 mA by pulling the output high
with an external resistor (Figure 1). Use following equation for
the POK to switch to high at a VOL and to low at
[VOL – VHYSTERESIS].
VOL + 1.3
(R7 ) R8)
R8
Volts
VHYSTERESIS + 50
(R7 ) R8)
R8
mVolts
(4)
VIN
(VOL – VHYSTERESIS)
(VOL)
FIGURE 8. VOUT (V)
Synchronization
Systems using more than one converter for power
management functions often face EMC problems. The
reflected ripple at the inputs from these independent
converters, which operate at different frequencies and phases,
can create a wide frequency range of harmonics. Obviously, it
is difficult, if not impossible, to eliminate all of these from the
emission spectrum. The alternatives are to incorporate a
heavy filter at the input of each converter or let all converters
oscillate at the same frequency and phase.
Document Number: 70959
07-Jul-99
www.vishay.com S FaxBack 408-970-5600
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet AN727.PDF ] | |
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