EVALA5970AD STMicroelectronics, EVALA5970AD Datasheet - Page 21

• Manufacturer Part Number: EVALA5970AD
• Description: BOARD EVAL FOR A5970AD REG
• Manufacturer: STMicroelectronics

Specifications of EVALA5970AD

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.235 ~ 35V
• Current - Output: 1A
• Voltage - Input: 4 ~ 36V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: A5970AD
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A5970AD
8
8.1
Application information
Component selection
●
The input capacitor must be able to support the maximum input operating voltage and the
maximum RMS input current.
Since step-down converters draw current from the input in pulses, the input current is
squared and the height of each pulse is equal to the output current. The input capacitor has
to absorb all this switching current, which can be up to the load current divided by two (worst
case, with duty cycle of 50%). For this reason, the quality of these capacitors has to be very
high to minimize the power dissipation generated by the internal ESR, thereby improving
system reliability and efficiency. The critical parameter is usually the RMS current rating,
which must be higher than the RMS input current. The maximum RMS input current (flowing
through the input capacitor) is:
Equation 17
Where η is the expected system efficiency, D is the duty cycle and I
current. This function reaches its maximum value at D = 0.5 and the equivalent RMS current
is equal to I
Equation 18
and
Equation 19
Input capacitor
O
divided by 2 (considering η = 1). The maximum and minimum duty cycles are:
Doc ID 14661 Rev 4
I
RMS
D
D
MAX
MIN
=
I
=
O
=
------------------------------------ -
V
•
------------------------------------- -
V
INMIN
V
INMAX
V
D 2 D
OUT
OUT
–
--------------- -
–
+
+
•
–
V
η
V
V
SW
V
F
2
F
SW
+
D
------ -
η
2
2
Application information
O
is the output DC
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