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參數(shù)資料
| 型號： | FAN5090 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Two Phase Interleaved Synchronous Buck Converter for VRM 9.x Applications |
| 中文描述： | 兩相交錯同步降壓轉換器的電源模組采用9.x中的應用 |
| 文件頁數(shù)： | 12/17頁 |
| 文件大?。?/td> | 183K |
| 代理商： | FAN5090 |
FAN5090
PRODUCT SPECIFICATION
12
REV. 1.0.1 9/16/03
pin for return. Typically, the BOOT pin will use a charge
pump as shown in Figure 2. Note that the BOOT and VCC
pins are separated from the chip’s internal power and ground,
BYPASS and AGND, for switching noise immunity.
Adaptive Delay Gate Drive
The FAN5090 embodies an advanced design that ensures
minimum MOSFET transition times while eliminating
shoot-through current. It senses the state of the MOSFETs
and adjusts the gate drive adaptively to ensure that they are
never on simultaneously. When the high-side MOSFET turns
off, the voltage on its source begins to fall. When the voltage
there reaches approximately 2.2V, the low-side MOSFETs
gate drive is applied. When the low-side MOSFET turns off,
the voltage at the LDRV pin is sensed. When it drops below
approximately 1.2V, the high-side MOSFET’s gate drive is
applied with 50ns delay.
Maximum Duty Cycle
In order to ensure that the current-sensing and charge-
pumping work, the FAN5090 guarantees that the low-side
MOSFET will be on a certain portion of each period. For low
frequencies, this occurs as a maximum duty cycle of approxi-
mately 90%. Thus at 250KHz, with a period of 4μsec, the
low-side will be on at least 4μsec 10% = 400nsec. At higher
frequencies, this time might fall so low as to be ineffective.
The FAN5090 provides a minimum low-side on-time of
approximately 330nsec, regardless of duty cycle.
Current Sensing
The FAN5090 has two independent current sensors, one for
each phase. Current sensing is accomplished by measuring
the source-to-drain voltage of the low-side MOSFET during
its on-time. Each phase has its own power ground pin, to per-
mit the phases to be placed in different locations without
affecting measurement accuracy. For best results, it is impor-
tant to connect the PGND and SW pins for each phase as a
Kelvin trace pair directly to the source and drain, respec-
tively, of the appropriate low-side MOSFET. Care is required
in the layout of these grounds; see the layout guidelines in
this datasheet.
Current Sharing
The two independent current sensors of the FAN5090 operate
with their independent current control loops to guarantee that
the two phases each deliver half of the total output current.
Mismatch between the two phases occurs only if there is a
mismatch between the R
DSon
of the low-side MOSFETs.
Short Circuit Current Characteristics (ILIM pin)
The FAN5090 short circuit current characteristic includes a
function that protects the DC-DC converter from damage in
the event of a short circuit. The short circuit limit is set with
the R
S
resistor, as given by the formula
with I
SC
the desired output current limit, R
T
the oscillator
resistor and R
DSon
one phase’s low-side MOSFET’s on resis-
tance. Remember to make the R
S
large enough to include the
effects of initial tolerance and temperature variation on the
MOSFETs’ R
DSon
.
Important Note!
The oscillator frequency must be selected
before selecting the current limit resistor, because the value
of RT is used in the calculation of R
S
.
When an overcurrent is detected, the high-side MOSFETs
are turned off, and the low-side MOSFETs are turned on,
and they remain in this state until the measured current
through the low-side MOSFET has returned to zero amps.
After reaching zero, the FAN5090 soft-starts, ensuring that it
can also safely turn on into a faulted load.
A limitation on the current sense circuit is that I
SC
R
DS,on
must be less that 375mV. To ensure correct operation, use
I
SC
R
DS,on
≤
300mV; between 300mV and 375mV. There
will be some non-linearity in the short-circuit current that is
not accounted for in the equation.
As an example, consider the typical characteristics of the
circuit using two FDD6696 low-side MOSFETs (8m
@
25°C, 10.4m
@ 95°C, each), R
T
= 56.2K, and R
S
= 75K:
The converter maintains a normal load regulation character-
istic until the voltage across the MOSFETs exceeds the
internal short circuit threshold of 75K / (3.33 x 56.2K x
5.2m
) = 77A. At this point, the internal comparator trips
and signals the controller to leave on the low-side MOSFETs
and keep off the high-side MOSFETs. The inductor current
decreases, and power is not applied again until inductor
current reaches 0A and the converter attempts a new
soft-start cycle.
Internal Voltage Reference
The reference included in the FAN5090 is a precision band-
gap voltage reference. Its internal resistors are precisely
trimmed to provide a near zero temperature coefficient (TC).
Based on the reference is the output from an integrated 5-bit
DAC. The DAC monitors the 5 voltage identification pins,
VID0-4, and scales the reference voltage from 1.100V to
1.850V in 25mV steps.
BYPASS Reference
The internal logic of the FAN5090 runs on 5V. To permit the
IC to run with 12V only, it produces 5V internally with a
linear regulator, whose output is present on the BYPASS pin.
This pin should be bypassed with a 100nF capacitor for noise
suppression. The BYPASS pin should not have any external
load attached to it.
Dynamic Voltage Adjustment
The FAN5090 can have its output voltage dynamically
adjusted to accommodate low power modes. The designer
must ensure that the transitions on the VID lines all occur
R
S
(
)
I
SC
R
DS on
R
T
3.33
=
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| FAN5090_ABC3026B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5090_ABC3116B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5090MTC | 功能描述:DC/DC 開關控制器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| FAN5090MTC_Q | 功能描述:DC/DC 開關控制器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
| FAN5090MTCX | 功能描述:DC/DC 開關控制器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 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 安裝風格: 封裝 / 箱體:CPAK |
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