AS1324 AMSCO [austriamicrosystems AG], AS1324 Datasheet - Page 13

• Manufacturer Part Number: AS1324
• Description: 1.5MHz, 600mA, DC/DC Step-Down Regulator
• Manufacturer: AMSCO [austriamicrosystems AG]

AS1324
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high volt-
age rating, and low ESR make them ideal for switching regulator applications. Because the AS1324 control loop is not
dependant on the output capacitor ESR for stable operation, ceramic capacitors can be used to achieve very low out-
put ripple and accommodate small circuit size.
At light loads, the converter operates in powersave mode and the output voltage ripple is in direct relation to the output
capacitor and inductor value used. Larger output capacitor and inductor values minimize the voltage ripple in power-
save mode and tighten DC output accuracy in powersave mode.
Input Capacitor Selection
In continuous mode, the source current of thePMOS is a square wave of the duty cycle V
age transients while minimizing the interference with other circuits caused by high input voltage spikes, a low ESR
input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given as:
where the maximum average output current I
I
This formula has a maximum at V
for design because even significant deviations only provide negligible affects.
The input capacitor can be increased without any limit for better input voltage filtering. Take care when using small
ceramic input capacitors. When a small ceramic capacitor is used at the input, and the power is being supplied through
long wires, such as from a wall adapter, a load step at the output, or V
pin. This ringing can then couple to the output and be mistaken as loop instability, or could even damage the part by
exceeding the maximum ratings.
Ceramic Input and Output Capacitors
When choosing ceramic capacitors for C
These dielectrics have the best temperature and voltage characteristics for a given value and size. Y5V and Z5U
dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequen-
cies and therefore should not be used.
Table 6. Recommended Input and Output Capacitor
Because ceramic capacitors lose a lot of their initial capacitance at their maximum rated voltage, it is recommended
that either a higher input capacity or a capacitance with a higher rated voltage is used.
Feedback Resistor Selection
In the AS1324-AD, the output voltage is set by an external resistor divider connected to V
cuitry allows for remote voltage sensing and adjustment.
www.austriamicrosystems.com
MAX
GRM188R60J106ME47
GRM21BR71A475KA73
JMK212BJ226MG-T
= I
Part Number
LIM
- ΔI
L
/2
4.7µF
22µF
10µF
IN
C
= 2V
I
RMS
OUT
IN
TC Code Rated Voltage
and C
where I
X5R
X5R
X7R
MAX
=
I
MAX
OUT
equals the peak current minus half the peak-to-peak ripple current,
RMS
, the X5R or X7R dielectric formulations are recommended.
Revision 1.03
×
----------------------------------------------------------- -
= I
V
OUT
6.3V
6.3V
OUT
10V
×
/2. This simple worst-case condition is commonly used
(
V
V
IN
IN
IN
–
step on the input, can induce ringing at the VIN
Dimensions (L/W/T)
V
OUT
)
0805
0603
0805
OUT
FB
/V
(see Figure
IN
Taiyo Yuden
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Murata
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. To prevent large volt-
Manufacturer
27). This cir-
13 - 20
(EQ 6)