ams Datasheet Page 17
[v1-11] 2015-Jan-28 Document Feedback
AS1310 − Detailed Description
Typically, the ripple due to ESR is not dominant. ESR for the
recommended capacitors (Murata GMR), ESR = 5mΩ to 10mΩ.
For the AS1310, maximum peak current is 480mA. Ripple due
to ESR is 2.4mV to 4.8mV.
Ripple at the input propagates through the common supply
connections, and if too high in value can cause problems
elsewhere in the system. The input capacitance is an important
component to get right.
Output Capacitor Selection
The output capacitor supports the triangular current during the
OFF-time of the power switch (inductor discharge period), and
also the load current during the wait time (Region D in
Figure 17) and ON-time (Region A in Figure 17) of the power
switch.
Note(s): There is also a ripple component due to the equivalent
series resistance (ESR) of the capacitor.
Summary
User Application Defines:
V
INmin
, V
INmax
, V
OUTmin
, V
OUTmax
, I
LOADmin
, I
LOADmax
Inductor Selection:
Select Max on-time = 0.5μs to 3μs for AS1310. Use EQ 3 to
calculate inductor value.
Use EQ 5 to determine OFF-time.
Use EQ 6 to check that power delivery matches load
requirements assume 70% conversion efficiency.
Use EQ 13 to find overall timing period value of T at min V
IN
and
max V
OUT
for maximum load conditions.
Input Capacitor Selection:
Choose a ripple value and use EQ 14 to find the value.
Output Capacitor Selection:
Determine T
WAIT
via EQ 6 or EQ 13, and use EQ 16 to find the
value.
NOMOUT
WAITONLOAD
OUT
V
TTI
C
_
)99.01(
)(
−
+
=
