EVALA5972D STMicroelectronics, EVALA5972D Datasheet - Page 17

• Manufacturer Part Number: EVALA5972D
• Description: Power Management Modules & Development Tools EVAL BOARD A5972 Auto Grade
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of EVALA5972D

• Input Voltage: 4.4 V to 36 V
• Output Voltage: 1.235 V to 35 V
• Board Size: 23 mm x 20 mm
• Product: Power Management Modules
• Supply Current: 2 A
• Dimensions: 23 mm x 20 mm
• For Use With/related Products: AN1517
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AN1517
5.1.2
5.1.3
Output capacitor
The output capacitor is very important to meet the output voltage ripple requirement.
Using a small inductor value is useful to reduce the size of the choke but it increases the
current ripple. So, to reduce the output voltage ripple, a low ESR capacitor is required.
Nevertheless, the ESR of the output capacitor introduces a zero in the open loop gain,
which helps to increase the phase margin of the system.
If the zero goes to a very high frequency, its effect is negligible. For this reason, ceramic
capacitors and very low ESR capacitors in general should be avoided.
Tantalum and electrolytic capacitors are usually good for this purpose.
Table 3
Table 3.
1. POSCAP capacitors have characteristic very similar to tantalum ones.
Inductor
The inductor value is very important because it fixes the ripple current flowing through
output capacitor.
The ripple current is usually fixed at 20-40% of I
A. The approximate inductor value is obtained using the following formula:
Equation 19
where T
For example, with V
21 µH.
The peak current through the inductor is given by:
Equation 20
and it can be observed that if the inductor value decreases, the peak current (which must be
lower than the current limit of the device) increases. So, when the peak current is fixed, a
higher inductor value allows a higher value for the output current.
In
Sanyo POSCAP
Table 4: Inductor
Manufacturer
Sprague
KEMET
below provides a list of some tantalum capacitor manufacturers.
ON
AVX
is the ON time of the internal switch, given by D · T.
Recommended output capacitors
(1)
OUT
selection, some inductor manufacturers are listed.
= 3.3 V, V
TPA/B/C
T494/5
Series
595D
TPS
L
IN
=
= 12 V and ∆I
(
-------------------------------------- -
V IN V OUT
I PK
Cap value (µF)
–
100 to 470
100 to 470
100 to 470
220 to 390
I ∆
=
I O
O
+
max, which is 0.3 - 0.6 A with I
O
I ∆
---- -
)
2
= 0.45 A, the inductor value is about
•
T ON
Rated voltage (V)
4 to 20
4 to 35
4 to 16
4 to 20
Application information
ESR (mΩ)
160 to 650
50 to 200
30 to 200
40 to 80
O
max = 1.5
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