SI-8050S Allegro Microsystems Inc, SI-8050S Datasheet - Page 5

• Manufacturer Part Number: SI-8050S
• Description: IC, LINEAR VOLTAGE REGULATOR 5V TO-220-5
• Manufacturer: Allegro Microsystems Inc

Specifications of SI-8050S

• Primary Input Voltage: 40V
• Output Voltage Fixed: 5V
• No. Of Outputs: 1
• No. Of Pins: 5
• Output Current: 3A
• Operating Temperature Range: -30°C To +125°C
• Power Dissipation Pd: 18W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

84
1. Selecting External Components
SI-8000S Series
(1) Choke coil L
To maintain the stable operation of the regulator, choke coil L
should be selected appropriately.
When selecting choke coil L
a) Suitable for a switching regulator
b) Appropriate inductance
c) Satisfying the rated current
d) Good DC current superposition characteristics
e) Less noise
Do not use a coil as a noise filter because it generates excess
heat.
The greater the inductance of the choke coil, the smaller the
output ripple voltage. However, the size of the coil increases
large as the inductance increases. If the inductance is low, a
greater peak current flows to the IC and loss increases. This
is not favorable for stable operation.
The standard external circuit shows reference inductance val-
ues suitable for stable operation. However, the appropriate
inductance may also be calculated as follows:
Where, deltaIL indicates the ripple current of the choke coil
that is roughly set as follows:
• If the working output current is close to the maximum rating
• If the working output current is about 1.0A or less
The rated current of a choke coil must be greater than the
maximum load current. Note that the inductance decreases
drastically and an excess current flows if the load current ex-
ceeds the rated current of the coil.
The current flowing through a choke coil is a triangular wave-
form current superimposed on a DC current equal to the load
current. The coil inductance decreases as the load current
increases. In general, the coil can be used until the induc-
tance drops to 50% of the rated value. Use this as the refer-
ence value for selection.
A drum-type open magnetic core coil can affect peripheral
circuits with noise because the flux passes outside the coil.
To avoid this problem, use a toroidal, EI, or EE type open
magnetic core coil.
(3 A) of SI-8000S
Ripple current = output current
Ripple current = output current
100%
1
50%
L=
(V
Caution
IN
IL•V
–V
Load current
O
Inductance
IN
)•V
•f
1
, consider the following:
O
0.2 to 0.3
0.3 to 0.4
I
O
(max.)
1
2. Notes on Pattern Design
(2) Input capacitor C
(3) Output capacitor C
(4) Diode D
(1) Large current line
(2) Input capacitor
Input capacitor C
circuit.
When selecting input capacitor C
a) The breakdown voltage is higher than the maximum input volt-
b) Satisfies the allowable ripple current
Output capacitor C
ing output. The output ripple voltage from the regulator is deter-
mined by the product of the pulsating current part IL (=C
discharge current) of the choke coil current and the equivalent
series resistance ESR of the output capacitor C
Therefore, a capacitor of low equivalent series resistance ESR
should be selected to reduce the output ripple voltage. It is rec-
ommended to select a low-impedance capacitor intended for use
with switching regulators as C
Use a Schottky barrier diode for D
diode or fast recovery diode, the IC may be damaged. (Sanken
RK46 recommended)
Since a large current flows through the bold lines in the standard
external circuit make the pattern as wide and as short as pos-
sible.
Place the input capacitor C
the IC as possible. Since a large current flows through the lead
wires of the input and output capacitors to charge and discharge
them quickly, minimize the lead wire length. The pattern around
the capacitors should also be minimized.
age.
Exceeding the ratings of this capacitor or using it without de-
rating may reduce its service life and also cause the regulator
to malfunction. Therefore, an input capacitor with a sufficient
margin should be selected. With the SI-8000S Series, the
effective ripple current Irms flowing to the input capacitor can
be calculated approximately as follows:
GND
Example of bad pattern
1
C
V
IN
1
+
I
V
C
rms
+
rip
1
. C
1
= IL•C2ESR
1
1
2
2
2
operates as a bypass capacitor in the input
1.2
operates as a smoothing capacitor for switch-
.
SI-8000S
3
V
V
1
IN
O
and output capacitor C
2
.
4
2
1
I
D
1
, consider the following:
O
. If you use a general rectifier
1
Example of good pattern
+
L
1
C
2
2
.
V
+
2
C
GND
OUT
as close to
1
. C
2
charge-
2
.