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參數(shù)資料
| 型號： | SI9122A |
| 廠商： | Vishay Intertechnology,Inc. |
| 英文描述： | 500-kHz Half-Bridge DC/DC Controller With Integrated Secondary Synchronous Rectification Drivers |
| 中文描述： | 500千赫半橋DC / DC變換器與集成的次級同步整流驅(qū)動(dòng)器控制器 |
| 文件頁數(shù)： | 9/15頁 |
| 文件大?。?/td> | 241K |
| 代理商： | SI9122A |
Si9122A
Vishay Siliconix
Document Number: 73492
S–51921—Rev. A, 12-Sep-05
www.vishay.com
9
Care needs to be taken if there is a delay prior to the external
circuit feeding back to the V
CC
supply. To prevent excessive
power dissipation within the IC it is advisable to use an external
PNP device. A pin has been incorporated on the IC,
(REG_COMP) to provide compensation when employing the
external device. In this case the V
IN
pin is connected to the
base of the PNP device and controls the current, while the
REG_COMP pin determines the frequency compensation of
the circuit. To understand the operation please refer to
Figure 5
.
The soft-start circuit is designed for the dc-dc converter to
start-up in an orderly manner and reduce component stress on
the IC. This feature is programmable by selecting an external
C
SS
. An internal 20- A current source charges C
SS
from 0 V
to the final clamped voltage of 8 V. In the event of UVLO or
shutdown, V
SS
will be held low (<1 V) disabling driver
switching. To prevent oscillations, a longer soft-start time may
be needed for highly capacitive loads and/or high peak output
current applications.
Reference
The reference voltage of Si9122A is set at 3.3 V. The reference
voltage should be de-coupled externally with 0.1- F capacitor.
The V
REF
voltage is 0 V in shutdown mode and has 50-mA
source capability.
Voltage Mode PWM Operation
Under normal load conditions, the IC operates in voltage mode
and generates a fixed frequency pulse width modulated signal
to the drivers. Duty cycle is controlled over a wide range to
maintain output voltage under line and load variation. Voltage
feed forward is also included to take account of variations in
supply voltage V
IN
.
In the half-bridge topology requiring isolation between output
and input, the reference voltage and error amplifier must be
supplied externally, usually on the secondary side. The error
information is thus passed to the power controller through an
opto-coupling device. This information is inverted, hence 0 V
represents the maximum duty cycle, whilst 2 V represents
minimum duty cycle. The error information enters the IC via pin
EP, and is passed to the PWM generator via an inverting
amplifier. The relationship between Duty cycle and V
EP
is
shown in the Typical Characteristic Graph,
Duty Cycle vs. V
EP
25 C
, page 11. Voltage feedforward is implemented by taking
the attenuated V
IN
signal at V
INDET
and directly modulating the
duty cycle.
At start-up, i.e., once V
CC
is greater than V
UVLO
, switching is
initiated under soft-start control which increases primary
switch on-times linearly from D
MIN
to D
MAX
over the soft-start
period. Start-up from a V
INDET
power down is also initiated
under soft-start control.
Half-Bridge and Synchronous Rectification Timing
Sequence
The PWM signal generated within the Si9122A controls the
low and high-side bridge drivers on alternative cycles. A period
of inactivity always results after initiation of the soft-start cycle
until the soft-start voltage reaches approximately 1.2 V and
PWM controlled switching begins. The first bridge driver to
switch is always the low-side (D
L
), as this allows charging of
the high-side boost capacitor.
The timing and coordination of the drives to the primary and
secondary stages is very important and shown in
Figure 3
. It
is essential to avoid the situation where both of the secondary
MOSFETs are on when either the high or the low-side switch
are active. In this situation the transformer would effectively be
presented with a short across the output. To avoid this, a
dedicated break-before-make circuit is included which will
generate non overlapping waveforms for the primary and the
secondary drive signals. This is achieved by a programmable
timer which delays the switching on of the primary driver
relative to the switching off of the related secondary and
subsequently delays the switching on of the secondary relative
to the switching off of the related primary.
Typical variations of BBM times with respect to R
BBM
and other
operating parameters are shown on page 13 and 14.
Primary High- and Low-Side MOSFET Drivers
The drive voltage for the low-side MOSFET switch is provided
directly from V
CC
. The high-side MOSFET however requires
the gate voltage to be enhanced above V
IN
. This is achieved
by bootstrapping the V
CC
voltage onto the L
X
voltage (the
high-side MOSFET source). In order to provide the
bootstrapping an external diode and capacitor are required as
shown on the application schematic. The capacitor will charge
up after the low-side driver has turned on. The switch gate
drive signals D
H
and D
L
are shown in
Figure 3
.
Secondary MOSFET Drivers
The secondary side MOSFETs are driven from the Si9122A
via a center tapped pulse transformer and inverter drivers. The
waveforms from SRH and SRL are shown in
Figure 3
. Of
importance is the relative voltage between SRH and SRL, i.e.
that which is presented across the primary of the pulse
transformer. When both potentials of SRL and SRH are equal
then by the action of the inverting drivers both secondary
MOSFETs are turned on.
Oscillator
The oscillator is designed to operate at a nominal frequency of
500 kHz. The 500-kHz operating frequency allows the converter
to minimize the inductor and capacitor size, improving the power
density of the converter. The oscillator and therefore the
switching frequency is programmable by attaching a resistor to
the R
OSC
pin. Under overload conditions the oscillator frequency
is reduced by the current overload protection to enable a constant
current to be maintained into a low impedance circuit.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SI9122A_08 | 制造商:VISHAY 制造商全稱:Vishay Siliconix 功能描述:500-kHz Half-Bridge DC/DC Controller with Integrated Secondary Synchronous Rectification Drivers |
| SI9122ADLP-T1-E3 | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 500kHz DC/DC Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| SI9122ADQ-T1-E3 | 功能描述:DC/DC 開關(guān)控制器 500kHz DC/DC Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| SI9122DLP-T1-E3 | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 500kHz DC/DC Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| SI9122DQ | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 500kHz DC/DC Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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