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| 型号： | MC33260DR2 |
| 厂商： | ON Semiconductor |
| 文件页数： | 11/22页 |
| 文件大小： | 372K |
| 描述： | IC PFC COMPACT PRECONVERT 8SOIC |
| 产品变化通告： | LTB Notification 03/Jan/2008 |
| 标准包装： | 1 |
| 系列： | GreenLine™ |
| 模式： | 间歇导电（DCM） |
| 电流 - 启动： | 100µA |
| 电源电压： | 11 V ~ 16 V |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOICN |
| 包装： | 剪切带 (CT) |
| 其它名称： | MC33260DR2OSCT |
MC33260
http://onsemi.com
11
Pin Numbers are Relevant to the PDIP- -8 Version
Thisequationshowsthatthemaximumon- -timeisinversely
proportional to the squared output voltage. This property is
used for follower boost operation (refer to Follower Boost
section).
CURRENT SENSE BLOCK
The inductor current is converted into a voltage by
insertingagroundreferencedresistor(R
cs
)inserieswiththe
input diodes bridge (and the input filtering capacitor).
Therefore a negative voltage proportional to the inductor
current is built:
V
cs
= - -
r
R
cs
?I
L
u
where:
I
L
is the inductor current,
R
cs
is the current sense resistor,
V
cs
is the measured R
cs
voltage.
Figure 27. Current Sensing
V
OCP
--60 mV
Zero Current Detection
Time
V
OCP
= R
OCP
?I
OCP
An overcurrent is detected if V
pin4
crosses the threshold (--60 mV)
during the Power Switch on state
The negative signal V
cs
is applied to the current sense
througharesistor R
OCP
.The pinisinternallyprotected bya
negative clamp (- -0.7 V) that prevents substrate injection.
As long as the Pin 4 voltage is lower than (- -60 mV), the
CurrentSensecomparatorresetsthePWMlatchtoforcethe
gate drive signal low state. In that condition, the power
MOSFET cannot be on.
During the on- -time, the Pin 4 information is used for the
overcurrent limitation while it serves the zero current
detection during the off time.
Zero Current Detection
The Zero Current Detection function guarantees that the
MOSFET cannot turn on as long as the inductor current
hasnt reached zero (discontinuous mode).
The Pin 4 voltage is simply compared to the (- -60 mV)
threshold so that as long as V
cs
is lower than this threshold,
the circuit gate drive signal is kept in low state.
Consequently, no power MOSFET turn on is possible until
theinductorcurrentismeasuredassmallerthan(60mV/R
cs
)
that is, the inductor current nearly equals zero.
Figure 28. Current Sense Block
1
0
I
ocp
(205 mA)
Output_Ctrl
LEB
--
+
--60 mV
PWM
Latch
R
S
Q
Output_Ctrl
R
4
To Output Buffer
(Output_Ctrl Low <=> Gate Drive in Low State)
R
OCP
V
OCP
R
cs
D1...D4
Overcurrent Protection
During the power switch conduction (i.e. when the Gate
Drive Pin voltage is high), a current source isapplied to the
Pin 4. A voltage drop V
OCP
is then generated across the
resistor R
OCP
that is connected between the sense resistor
and the Current Sense Pin (refer to Figure 28). So, instead
of V
cs
, the sum (V
cs
+ V
OCP
) is compared to (- -60 mV) and
the maximum permissible current is the solution of the
following equation:
- -
r
R
cs
?Ipk
max
u
+ V
OCP
= - -60 mV
where:
Ipk
max
is maximum allowed current,
R
cs
is the sensing resistor.
The overcurrent threshold is then:
Ipk
max
=
r
R
OCP
?I
OCP
u
+ 60 ?10
- -3
R
cs
where:
R
OCP
is the resistor connected between the pin and the
sensing resistor (R
cs
),
I
OCP
is the current supplied by the Current Sense Pin
when the gate drive signal is high (power switch
conduction phase). I
OCP
equals 205 mA typically.
Practically, the V
OCP
offset is high compared to 60 mV
andtheprecedentequationcanbesimplified.Themaximum
current is then given by the following equation:
Ipk
max
H
R
OCP
(k?
R
cs
(
?/DIV>
)
?0.205
(
A
)
Consequently,theR
OCP
resistorcanprogramtheOCPlevel
whatever the R
cs
value is. This gives a high freedom in the
choice of R
cs
. In particular, the inrush resistor can be utilized.
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