AS1341 austriamicrosystems AG, AS1341 Datasheet - Page 12

• Manufacturer Part Number: AS1341
• Description: Step-Down Converter
• Manufacturer: austriamicrosystems AG

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AS1341
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Output Capacitor
Choose the output capacitor to service the maximum load current with acceptable voltage ripple. The output ripple has
two components: variations in the charge stored in the output capacitor with each LX pulse, and the voltage drop
across the capacitor’s equivalent series resistance (ESR) caused by the current into and out of the capacitor:
The output voltage ripple as a consequence of the ESR and output capacitance is:
Where:
I
Equations 7, 8, and
or evaluation circuit. As a general rule, a smaller amount of charge delivered in each pulse results in less output ripple.
Since the amount of charge delivered in each oscillator pulse is determined by the inductor value and input voltage, the
voltage ripple increases with larger inductance, and as the input voltage decreases.
Table 6. Recommended Output Capacitor
Input Capacitor
The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on
the input caused by the circuit’s switching. The input capacitor must meet the ripple-current requirement (I
imposed by the switching current defined as:
For most applications, non-tantalum type (ceramic, aluminum, polymer, or OS-CON) are preferred due to their robust-
ness to high in-rush currents typical of systems with low-impedance battery inputs. Alternatively, connect two (or more)
smaller value low-ESR capacitors in parallel to reduce cost. Choose an input capacitor that exhibits less than +10ºC
temperature rise at the RMS input current for optimal circuit life.
Table 7. Recommended Input Capacitor
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PEAK
T520V107M010ATE018
A700V826M006ATE018
T520B107M006ATE040
T520A336M006ATE070
A700V226M006ATE028
510X107M020ATE040
10µF
is the peak inductor current
EEFCD0K330R
C
EEFUD0J101R
10TPB100ML
Part Number
6TPB47M
TC Code Rated Voltage
V
RIPPLEC
X7R
9
are suitable for initial capacitor selection, but actual values should be set by testing a prototype
I
= (L x (I
RMS
= (I
100µF
100µF
100µF
100µF
25V
82µF
33µF
22µF
10µF
33µF
47µF
PEAK
LOAD
C
(see Inductor Selection on page
- I
x V
V
OUTPUT
RIPPLE
OUTPUT
V
RIPPLEESR
18mΩ
18mΩ
40mΩ
70mΩ
28mΩ
40mΩ
15mΩ
18mΩ
55mΩ
70mΩ
ESR
≅ V
)2)/(2 x (C
)/V
Circuit
RIPPLEESR
IN
1-5
Revision 1.00
Rated Voltage
x
= ESR x I
√
OUT
((4/3) x (V
6.3V
6.3V
6.3V
6.3V
6.3V
10V
20V
10V
6V
8V
+ V
x V
PEAK
RIPPLEC
OUTPUT
Murata
Taiyo Yuden
Kemet
Panasonic
Sanyo
10). The worst-case ripple occurs at no-load.
IN
- V
)) x V
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www.edc.sanyo.com
OUTPUT
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IN
Circuit
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/(V
1,
1,
1,
3,
3,
1,
3,
1,
3,
) - 1)
5
IN
2
2
2
4
4
2
4
2
4
Manufacturer
- V
OUTPUT
Kemet
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Panasonic
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Sanyo
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)
Manufacturer
RMS
)
(EQ 10)
12 - 16
(EQ 7)
(EQ 8)
(EQ 9)