參數(shù)資料
型號(hào): FL6961MY
廠商: Fairchild Semiconductor
文件頁(yè)數(shù): 9/11頁(yè)
文件大?。?/td> 489K
描述: IC CTLR PFC SGL FLYBACK 8-SOIC
標(biāo)準(zhǔn)包裝: 2,500
模式: 臨界傳導(dǎo)(BCM)
電流 - 啟動(dòng): 10µA
電源電壓: 10.5 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: 帶卷 (TR)
 
?2010 Fairchild Semiconductor Corporation
 
www.fairchildsemi.com
FL6961 " Rev. 1.0.2
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 2.5V ?% 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.
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 a high resistance,
low-wattage startup resistor. For example, 1M&/0.25W
startup resistor and a 10礔/25V (V
CC
 hold-up) capacitor
are recommended for an AC-to-DC power adaptor with
a wide input range 85-265V
AC
.
Operating Current
Operating current is typically 4.5mA. The low operating
current   enables   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:
h
?/DIV>
?/DIV>
?/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 24k& resistor
R
I
 generates corresponds to 25祍 maximum on time:
(  )
s
k
R
t
I
on
m
24
25
)
(
(max)
?/DIV>
W
=
 
(2)
The range of the maximum on-time is 10 ~ 50祍.  
Peak Current Limiting
The switch current is sensed by one resistor. The signal
is fed into the CS pin and an input terminal of a
comparator. A high voltage on the CS pin terminates
the switching cycle immediately and cycle-by-cycle
current limit is achieved. The designed threshold of the
protection point is 0.82V.
Leading-Edge Blanking (LEB)
A turn-on spike on the 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 voltages are fixed
internally at 12V and 9.5V, respectively. 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 1M& R
IN
  is sufficient for
startup under low input line voltage, 85V
rms
. Power
dissipation on R
IN
 would be less than 0.1W even under
high line (V
AC
=265V
rms
) condition.
Output Driver
With   low   on   resistance   and   high   current   driving
capability, the output driver can drive an external
capacitive load larger than 3000pF. Cross conduction
current has been avoided to minimize heat dissipation,
improving efficiency and reliability. This output driver is
internally clamped by a 16.5V 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 Boundary
Mode. Slope compensation and a built-in debounce
circuit can alleviate this problem. Because the FL6961
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
FL6961,   and   increasing   the   power   MOSFET   gate
resistance all improve performance.
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