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參數(shù)資料
| 型號(hào)： | FAN5091 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Synchronous Multi-Slice DC-DC Controller(同步多片DC-DC轉(zhuǎn)換控制器) |
| 中文描述： | 同步多層DC - DC控制器（同步多片的DC - DC轉(zhuǎn)換控制器） |
| 文件頁數(shù)： | 15/20頁 |
| 文件大小： | 116K |
| 代理商： | FAN5091 |
FAN5091
15
A
Current Sharing
The two independent current sensors of the FAN5091 operate
with their independent current control loops to guarantee that
the two slices each deliver half of the total output current.
The only mismatch between the two slices occurs if there is a
mismatch between the R
DS,on
of the low-side MOSFETs.
Short Circuit Current Characteristics
The FAN5091 short circuit current characteristic includes a
hysteresis function that prevents the DC-DC converter from
oscillating 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 current limit, RT the oscillator resistor
and R
DS,on
the one slice’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
DS,on
.
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 RC5091 re-soft-starts, ensuring that
it can also safely turn on into a short.
As an example, consider the typical characteristic of the
DC-DC converter circuit with two FDP6670AL low-side
MOSFETs (R
DS
= 6.5m
maximum at 25
°
C * 1.2 at 75
°
C
= 7.8m
each, or 3.9m
total) in each slice, RT = 42.1K
(600KHz oscillator) and a 100K
R
S
.
The converter exhibits a normal load regulation characteris-
tic until the voltage across the MOSFETs exceeds the inter-
nal short circuit threshold of 100K
/(3.9m
* 41.2K
*
10) = 62A. [Note that this current limit level can be as high
as 100K
/(3.5m
* 41.2K
* 10) = 75A, if the MOSFETs
have typical R
DS,on
rather than maximum, and are at 25
°
C.]
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 the inductor current
reaches 0A and the converter attempts to re-softstart.
Precision Current Sensing
The tolerances associated with the use of MOSFET current
sensing can be circumvented by the use of a current sense
resistor, as provided for by the FAN5092.
Light Load Efficiency
At light load, the FAN5091 uses a number of techniques to
improve efficiency. Because a synchronous buck converter is
two quadrant, able to both source and sink current, during
light load the inductor current will flow away from the out-
put and towards the input during a portion of the switching
cycle. This reverse current flow is detected by the RC5091 as
a positive voltage appearing on the low-side MOSFET dur-
ing its on-time. When reverse current flow is detected, the
low-side MOSFET is turned off for the rest of the cycle, and
the current instead flows through the body diode of the high-
side MOSFET, returning the power to the source. This tech-
nique substantially enhances light load efficiency.
E*-mode
In addition, further enhancement in efficiency can be obtained
by putting the RC5091 into E*-mode. When the Droop pin is
pulled to above the 7.5V BYPASS voltage, the “B” slice of
the RC5091 is completely turned off, reducing in half the
amount of gate charge power being consumed. E*-mode can
be implemented with the circuit shown in Figure 5:
Figure 5. Implementing E*-mode Control
Internal Voltage Reference
The reference included in the FAN5091 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 0.950V to
1.700V in 25mV steps.
BYPASS Reference
The internal logic of the FAN5091 runs on 7.5V. To permit
the IC to run with 12V only, it produces 7.5V 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 have a maxi-
mum of 1mA external load attached to it.
Dynamic Voltage Adjustment
The RC5091 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
simultaneously (within less than
500
nsec) to avoid false codes
generating undesired output voltages. The Power Good flag
tracks the VID codes, but has a 10msec delay transitioning
from high to low; this is long enough to ensure that there will
not be any glitches during dynamic voltage adjustment.
R
S
I
SC
R
Ds on
RT
10
=
+12V
10K
1K
10K
2N2222
2N2907
R
DROOP
RC5091
pin21
HI = E*-
mode on
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| FAN5091_CAB3116B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5091MTC | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| FAN5091MTC_Q | 功能描述:DC/DC 開關(guān)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(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 |
| FAN5091MTCX | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| FAN5091MTF | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 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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