參數(shù)資料
型號: FAN6961SZ
廠商: Fairchild Semiconductor
文件頁數(shù): 9/13頁
文件大?。?/td> 738K
描述: IC PFC CONTROLLER DCM 8SOP
標(biāo)準(zhǔn)包裝: 1
模式: 間歇導(dǎo)電(DCM)
頻率 - 開關(guān): 60kHz
電流 - 啟動: 10µA
電源電壓: 13.5 V ~ 24.5 V
工作溫度: -40°C ~ 125°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應(yīng)商設(shè)備封裝: 8-SOP
包裝: 標(biāo)準(zhǔn)包裝
產(chǎn)品目錄頁面: 1222 (CN2011-ZH PDF)
其它名稱: FAN6961SZDKR
 
?2013 Fairchild Semiconductor Corporation
 
www.fairchildsemi.com
FAN6961 " Rev. 1.0.6
9
Functional Description
Error Amplifier
The inverting input of the error amplifier is referenced to
INV. The output of the error amplifier is referenced to
COMP. The non-inverting input is internally connected
to a fixed 2.5 V ?2% voltage. The output of the error
amplifier is used to determine the on-time of the PWM
output and regulate the output voltage. To achieve a
low input current THD, the variation of the on time within
one input AC cycle should be very small. A multi-vector
error amplifier is built in to provide fast transient
response and precise output voltage clamping.
For FAN6961, connecting a capacitance, such as 1 礔,
between COMP and GND is suggested. The error
amplifier is a trans-conductance amplifier that converts
voltage to current with a 125 祄ho.
Startup Current
Typical startup current is less than 20 礎(chǔ). This ultra-low
startup current allows the usage of high resistance, low-
wattage startup resistor. For example, 1 M&/0.25 W
startup   resistor   and   a   10 礔/25 V   (V
CC
   hold-up)
capacitor are recommended for an AC-to-DC power
adaptor with a wide input range 85-265 V
AC
.
Operating Current
Operating current is typically 4.5 mA. The low operating
current enables a better efficiency and reduces the
requirement of V
CC
 hold-up capacitance.
Maximum On-Time Operation
Given a fixed inductor value and maximum output
power,   the   relationship   between   on-time   and   line
voltage is:
?/DIV>
"
"
"
=
2
2
rms
o
on
V
P
L
t
 
(1)
If the line voltage is too low or the inductor value is too
high, t
ON
  is too long. To avoid extra low operating
frequency   and   achieve   brownout   protection,   the
maximum value of t
ON
 is programmable by one resistor,
R
I
, connected between MOT and GND. A 24 k& resistor
R
I
 generates corresponds to 25 祍 maximum on time:
(  )
s
k
R
t
I
on
?/DIV>
24
25
)
(
(max)
"
?/DIV>
=
 
(2)
The range of the maximum on-time is designed as 10 ~
50 祍.  
Peak Current Limiting
The switch current is sensed by one resistor. The signal
is   feed   into   CS   pin   and   an   input   terminal   of   a
comparator. A high voltage in CS pin terminates a
switching cycle immediately and cycle-by-cycle current
limit   is   achieved.   The   designed   threshold   of   the
protection point is 0.82 V.
Leading-Edge Blanking (LEB)
A turn-on spike on CS pin appears when the power
MOSFET is switched on. At the beginning of each
switching pulse, the current-limit comparator is disabled
for around 400ns to avoid premature termination. The
gate drive output cannot be switched off during the
blanking   period.   Conventional   RC   filtering   is   not
necessary, so the propagation delay of current limit
protection can be minimized.
Under-Voltage Lockout (UVLO)
The turn-on and turn-off threshold voltage is fixed
internally   at   12 V/9.5 V.   This   hysteresis   behavior
guarantees   a   one-shot   startup with proper startup
resistor and hold-up capacitor. With an ultra-low startup
current of 20 礎(chǔ), one 1 M& R
IN
 is sufficient for startup
under low input line voltage, 85 V
rms
. Power dissipation
on R
IN
 would be less than 0.1 W even under high line
(V
AC
=265 V
rms
) condition.
Output Driver
With   low   on   resistance   and   high   current   driving
capability, the output driver can drive an external
capacitive load larger than 3000 pF. Cross conduction
current has been avoided to minimize heat dissipation,
improving efficiency and reliability. This output driver is
internally clamped by a 16.5 V Zener diode.
Zero-Current Detection (ZCD)
The zero-current detection of the inductor is achieved
using its auxiliary winding. When the stored energy of
the inductor is fully released to output, the voltage on
ZCD goes down and a new switching cycle is enabled
after a ZCD trigger. The power MOSFET is always
turned on with zero inductor current such that turn-on
loss and noise can be minimized. The converter works
in boundary-mode and peak inductor current is always
exactly twice of the average current. A natural power
factor correction function is achieved with the low-
bandwidth, on-time modulation. An inherent maximum
off time is built in to ensure proper startup operation.
This ZCD pin can be used as a synchronous input.
Noise Immunity
Noise on the current sense or control signal can cause
significant pulse-width jitter, particularly in the boundary-
mode   operation.   Slope   compensation   and   built-in
debounce circuit can alleviate this problem. Because
the FAN6961 has a single ground pin, high sink current
at the output cannot be returned separately. Good high-
frequency or RF layout practices should be followed.
Avoiding   long   PCB   traces   and   component   leads,
locating compensation and filter components near to the
FAN6961, and increasing the power MOSFET gate
resistance improve performance.
 
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