參數(shù)資料
型號： ISL8840AAUZ
廠商： INTERSIL CORP
元件分類： 穩(wěn)壓器
英文描述： High Performance Industry Standard Single-Ended Current Mode PWM Controller
中文描述： 1 A SWITCHING REGULATOR, 2000 kHz SWITCHING FREQ-MAX, PDSO8
封裝： ROHS COMPLIANT, PLASTIC, MO-187AA, MSOP-8
文件頁數(shù)： 12/15頁
文件大?。?/td> 313K
代理商： ISL8840AAUZ
12
FN6320.3
April 18, 2007
The current sense signal at the end of the ON time for CCM
operation is:
where V
CS
is the voltage across the current sense resistor,
L
s
is the secondary winding inductance, and I
O
is the output
current at current limit. Equation 13 assumes the voltage
drop across the output rectifier is negligible.
Since the peak current limit threshold is 1.00V, the total
current feedback signal plus the external ramp voltage must
sum to this value when the output load is at the current limit
threshold.
Substituting Equations 12 and 13 into Equation 14 and
solving for R
CS
yields
Adding slope compensation is accomplished in the
ISL884xA using an external buffer transistor and the RTCT
signal. A typical application sums the buffered RTCT signal
with the current sense feedback and applies the result to the
CS pin as shown in Figure 6.
Assuming the designer has selected values for the RC filter
(R
6
and C
4
) placed on the CS pin, the value of R
9
required
to add the appropriate external ramp can be found by
superposition.
2.05D R
6
6
The factor of 2.05 in Equation 16 arises from the peak
amplitude of the sawtooth waveform on RTCT minus a
base-emitter junction drop. That voltage multiplied by the
maximum duty cycle is the voltage source for the slope
compensation. Rearranging to solve for R
9
yields:
The value of R
CS
determined in Equation 15 must be
rescaled so that the current sense signal presented at the
CS pin is that predicted by Equation 13. The divider created
by R
6
and R
9
makes this necessary.
R
9
V
CS
N
R
P
------------------------
I
O
1
D
–
(
-------------------------------------------
)
V
f
s
+
=
V
(EQ. 13)
V
e
V
CS
+
1
=
(EQ. 14)
R
CS
D f
V
p
-------------------------------
1
-------–
1
--
0.5
+
–
N
s
N
p
------
I
O
1
D
–
(
-------------------------------------------
)
V
f
s
+
+
----------------------------------------------------------------------------------------------------------------------------------------------------
=
(EQ. 15)
CS
RTCT
R6
C4
R9
I
VREF
FIGURE 6. SLOPE COMPENSATION
V
e
9
+
---------------------------
=
V
(EQ. 16)
R
9
2.05D
---------------------------------------------
V
–
e
(
)
R
6
=
Ω
(EQ. 17)
R
′
CS
R
9
+
--------------------
R
CS
=
(EQ. 18)
ISL8840A, ISL8841A, ISL8842A, ISL8843A, ISL8844A, ISL8845A
相關(guān)PDF資料
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ISL8840AMBZ High Performance Industry Standard Single-Ended Current Mode PWM Controller
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參數(shù)描述
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ISL8840AMBEP 制造商:Intersil Corporation 功能描述:CURRENT MODE PWM CNTRLR 1A 8SOIC N - Rail/Tube
ISL8840AMBEP-TK 制造商:Intersil Corporation 功能描述:CURRENT MODE PWM CNTRLR 1A 8SOIC N - Tape and Reel
ISL8840AMBEPZ 制造商:Intersil Corporation 功能描述:PB-FREE, -55 TO +125, CURRENT MODE PWM, 100% DC, 7.0V UVLO,8 - Rail/Tube
ISL8840AMBEPZ-TK 制造商:Intersil Corporation 功能描述:PB-FREE,-55 TO+125,CURRENT MODE PWM, 100% DC,7.0V UVLO,8LD S - Tape and Reel
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