ML4819CP_NL Fairchild Semiconductor, ML4819CP_NL Datasheet - Page 11

• Manufacturer Part Number: ML4819CP_NL
• Manufacturer: Fairchild Semiconductor

Specifications of ML4819CP_NL

• Start-up Supply Current: 600uA
• Operating Supply Voltage (max): 35V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Package Type: PDIP
• Pin Count: 20
• Mounting: Through Hole
• Lead Free Status / RoHS Status: Compliant

The value of R
(pin 6).
The peak of the inductor current can be found
approximately by:
Next select N
current. Assume 4A for this example. N
Where R
clamp at the inverting input of the PWM comparator. This
clamp is internally set to 5V. In actual application it is a
good idea to assume a value less than 5V to avoid
unwanted current limiting action due to component
tolerances. In this application V
Having calculated R
now be calculated:
Choose R18 = 33k
The following values were used in the calculation:
REV. 1.0 10/10/2000
Choose R9 = 27k
R
R
I
R
R
R
S
LPEAK
2
11
PWM
18
18
9
R
R
11
V
V
9
T
V
V
A
0 7
IN MAX PEAK
IN MIN PEAK
I
CLAMP
SINE PEAK
is the sense resistor, and V
= 27k
= 14k
CLAMP
.
SC
(
(
1 414
380
V
C
I
.
LPEAK
9
IN MIN RMS
, which depends on the maximum switch
(
2
( .
(pin 3) depends on the selection of R
0 225 10
V
mH
S
(
)
)
2 5
PWM
.
R
N
)
11
2 5 28 8
20
P
2
)
OUT
C
.
R
the value S
9
R
4 8 510
260 1 414
100
80 1 414
4 9 80
T
.
80
6
0 72
.
)
.
.
1 414 200
4
C
.
k
14
CLAMP
T
mA
.
0 225
.
k
90
.
A
C
k
PWM
SC
T
100
= 1nF
was chosen as 4.8V.
CLAMP
V
1
= 0.7
nF
C
510
22
/
and of R
is 80 turns.
k
s
3 14
k
30
.
is the current
k
A
18
can
2
(12)
(13)
(14)
(15)
(16)
VOLTAGE REGULATION COMPONENTS
The values of the voltage regulation loop components are
calculated based on the operating output voltage. Note
that voltage safety regulations require the use of sense
resistors that have adequate voltage rating. As a rule of
thumb if 1/4W through-hole resistors are used, two of
them should be put in series. The input bias current of the
error amplifier is approximately 0.5 A, therefore the
current available from the voltage sense resistors should
be significantly higher than this value. Since two 1/4W
resistors have to be used the total power rating is 1/2W.
The operating power is set to be 0.4W then with 380V
output voltage the value can be calculated as follows:
Choose two 178k , 1% connected in series.
Then R6 can be calculated using the formula below:
Choose 4.75k , 1%. One more critical component in the
voltage regulation loop is the feedback capacitor for the
error amplifier. The voltage loop bandwidth should be set
such that it rejects the 120Hz ripple which is present at
the output. If this ripple is not adequately attenuated it
will cause distortion on the input current waveform.
Typical bandwidths range anywhere from a few Hertz to
15Hz. The main compromise is between transient
response and distortion. The feedback capacitor can be
calculated using the following formula:
R
R
C
C
5
6
8
8
(
V
380
V
3 142
3 142 356
REF
B
.
.
V
V
) / .
2
REF
R
1
R
5
0 4
5
1
k
W
5
BW
380
V
V
360
2
356
Hz
5
k
k
V
0 44
.
4 747
.
F
k
ML4819
(17)
(18)
(19)
11