參數(shù)資料
型號(hào)： FAN6520AIM
廠商： FAIRCHILD SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： Single Synchronous Buck PWM Controller
中文描述： 1 A SWITCHING CONTROLLER, 340 kHz SWITCHING FREQ-MAX, PDSO8
封裝： MS-012AA, SOIC-8
文件頁(yè)數(shù)： 6/15頁(yè)
文件大小： 580K
代理商： FAN6520AIM
6
REV. 1.0.2 8/26/04
FAN6520A
PRODUCT SPECIFICATION
Circuit Description
Initialization
The FAN6520A automatically initializes upon receipt of
power. The Power-On Reset (POR) function continually
monitors the bias voltage at the VCC pin. When the supply
voltage exceeds its POR threshold, the IC initiates the
Over-current Protection (OCP) sample and hold operation.
Upon completion of the OCP sampling and hold operation,
the POR function initiates the soft-start operation.
Over-Current Protection
The over-current function protects the converter from a
shorted output by using the upper MOSFET’s on-resistance,
R
DS(ON)
, to monitor the current. This method enhances the
converter’s efficiency and reduces cost by eliminating the
need for a current-sensing resistor. The over-current function
cycles the soft-start function in a hiccup mode to provide
fault protection. A resistor (R
OCSET
current trip level (see Typical Application diagram).
Immediately following POR, the FAN6520A initiates the
Over-current Protection sampling and hold operation. First,
the internal error amplifier is disabled. This allows an inter-
nal 20μA current sink to develop a voltage across R
The FAN6520A then samples this voltage at the COMP pin.
This sampled voltage, which is referenced to the VCC pin,
is held internally as the Over-current Set Point. When the
voltage across the upper MOSFET, which is also referenced
to the VCC pin, exceeds the Over-current Set Point, the
over-current function initiates a soft-start sequence. Figure 3
shows the inductor current after a fault is introduced while
running at 15A. The continuous fault causes the FAN6520A
to go into a hiccup mode with a typical period of 25ms. The
inductor current increases to 18A during the soft-start inter-
val and causes an over-current trip. The converter dissipates
very little power with this method. The measured input
power for the conditions shown in Figure 3 is only 1.5W.
) programs the over-
OCSET
.
Figure 3. Over-Current Operation
The over-current function will trip at a peak inductor current
(I
PEAK
) determined by:
where I
typical). The OC trip point varies mainly due to the
MOSFET’s R
DS(ON)
variations. To avoid over-current
tripping in the normal operating load range, find the R
resistor from the equation above with:
OCSET
is the internal OCSET current source (20μA
OCSET
1.
The maximum R
temperature.
DS(ON)
at the highest junction
2.
The minimum I
OCSET
for
from the specification table.
3.
Determine I
where
PEAK
,
I is the output inductor ripple current.
For an equation for the ripple current see “Output Inductor
(L
out
)” under Component Selection.
Internal circuitry of the FAN6520A will not recognize a volt-
age drop across R
OCSET
larger than 0.5V. Any voltage drop
across R
OCSET
that is greater than 0.5V will set the overcur-
rent trip point to:
An overcurrent trip cycles the soft-start function.
Soft-Start
The POR function initiates the soft-start sequence after the
over-current set point has been sampled. Soft-start clamps
the error amplifier output (COMP pin) and reference input
(noninverting terminal of the error amp) to the internally
generated soft-start voltage. Figure 4 shows a typical start up
interval where the COMP/OCSET pin has been released
from a grounded (system shutdown) state. Initially, the
COMP/OCSET is used to sample the over-current setpoint
by disabling the error amplifier and drawing 20μA through
R
OCSET
. Once the over-current level has been sampled, the
soft-start function is initiated. The clamp on the error
amplifier (COMP/OCSET pin) initially controls the
converter’s output voltage during soft-start. The oscillator’s
triangular waveform is compared to the ramping error
amplifier voltage. This generates SW pulses of increasing
width that charge the output capacitor(s). When the inter-
nally generated soft-start voltage exceeds the feedback (FB
pin) voltage, the output voltage is in regulation. This method
provides a rapid and controlled output voltage rise. The
entire startup sequence typically takes about 11ms.
OUTPUT INDUCTOR
CURRENT
5A/DIV.
I
PEAK
I
-----------R
R
×
DS ON
)
=
(1)
I
PEAK
I
OUT MAX
)
I
2
-----
+
>
I
PEAK
DS ON
)
R
=
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FAN6520AIMX 功能描述:電壓模式 PWM 控制器 ANG FG SynchBuck Regulator- 8ld RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AM 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AM_Q 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AMX 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AMX_Q 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
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