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参数资料
型号： AS1339-BWLT
厂商： AUSTRIAMICROSYSTEMS AG
元件分类： DC/DC变换器
英文描述： 650mA Buck+2x10mA LDOs RF-PA; Package Type: CS-WLP-16
封装： CS-WLP-16
文件页数： 19/25页
文件大小： 4057K
代理商： AS1339-BWLT
wwwaustriamcrosystems.com/DC-DC_Step-Down/AS1339
Revision 1.05
19 - 25
AS1339
Datasheet - Application Information
Capacitor Selection for LDO’s
Input Capacitor
The capacitor for the LDO Input should have at least a value of the sum of the output capacitors of LDO1 and LDO2.
With a larger input capacitance and lower ESR a better noise rejection and line transient response can be achieved.
Output Capacitor
For the LDO outputs the capacitor value depends on the needed load current. For a stable operation with rated maxi-
mum load currents a minimum output capacitor of 1μF is recommended. At light loads of 10mA or less a 0.1μF capac-
itor is sufficient. With larger output capacitance a reduced output noise, improved load-transient response, better
stability and power-supply rejection can be achieved.
Inductor Selection
For most applications the value of the external inductor should be in the range of 1.5μH to 4.7μH as the inductor value
has a direct effect on the ripple current. The selected inductor must be rated for its DC resistance and saturation cur-
rent. The inductor ripple current (
Δ
I
L
) decreases with higher inductance and increases with higher V
IN
to V
OUT
.
In
Equation (EQ 3)
the maximum inductor current in PWM mode under static load conditions is calculated. The satura-
tion current of the inductor should be rated higher than the maximum inductor current as calculated with
Equation (EQ
4)
. This is recommended because the inductor current will rise above the calculated value during heavy load tran-
sients.
The inductor current ripple
Δ
I
L
(see EQ 3)
is defined by the slope of the current (dI / dt)
(see EQ 1)
multiplied by the
PFET on-time t
ON
(see EQ 2)
.
Figure 51. Ripple Current Diagram
Table 7. Recommended Capacitors for the LDO’s
Name
Part Number
C
Voltage
Type
Size
Manufacturer
KEMET
Murata
www.murata.com
C
IN2
, C
LDO1
,
C
LDO2
C0402C104K4RAC
100nF
16V
X7R
0402
GRM155R61A105KE15
1μF
10V
X5R
0402
t
ON
Δ
I
L
I
L
t
I
OUTmax
I
Lmax
dI
dt
1 / f
(EQ 1)
dt
dI
V
---------–
V
L
=
(EQ 2)
t
ON
DutyCycle
1
f
--
×
DutyCycle
V
V
IN
-------------
=
=
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