as1339 austriamicrosystems, as1339 Datasheet - Page 21

• Manufacturer Part Number: as1339
• Description: 650ma Rf Step-down Dc-dc For Pa, With Two Ldos
• Manufacturer: austriamicrosystems

AS1339
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 52. Efficiency Comparison of different
Example
The following system should be designed:
For the first step V
Due to
If V
Hence a 2.2µH coil is used, Δ I
With this result I
The saturation current of the coil should be chosen slightly higher than I
increase the peak current. For a short period of time (~50µs) the peak inductor current can rise up to a value of approx-
imately 1.1A (p-channel MOSFET peak current limit). In this case a coil with a rated saturation current of ~800mA can
be chosen.
Layout Considarations
High peak currents of up to 1.1A and a high switching frequency makes the PCB layout important. Following rules
should be considered:
www.austriamicrosystems.com
IN
100
- A supply with a Lithium-Ion Battery = 4.5V
- V
-
- The power traces (IN1A, IN1B, IN2, LX, PAA, PAB, PGND) should be kept as short, direct and wide as practical.
- All capacitors should be placed as close as possible near the device.
- Try to keep the serial resistance (ESR) of C
- The negative terminations of the capacitors C
90
80
70
60
50
40
30
20
10
I
starpoint to PGND is recommended.
is falling below 3.23V the device is going into Bypass mode
0
OUTMAX
OUT
10
Equation (EQ
Inductors; V
= 3.0V
= 500mA
MAX
REF
Output Current (mA)
can be calculated with
6): V
is calculated as shown in
IN
= 3.9V, V
IN
100
= 3.23V
L
can be calculated with
OUT
= 1.0V
MLP2520S1R5S
MLP2520S2R2S
MLP2520S3R3S
EPL2014-222
EPL2014-332
EPL2014-472
Equation (EQ
V
Equation (EQ
LDO1
REF
1000
V
OUT
IN
Revision 1.02
=
≤
and C
Equation (EQ
and C
2 69
V
-------------
,
2 5 ,
4): I
OUT
Figure 53. Efficiency Comparison of different
LDO2
×
IN
MAX
100
5).
=
V
90
80
70
60
50
40
30
20
10
should be kept as close to each other as possible. A
REF
0
1 2V
as low as possible.
(see Bypass Mode on page
= 614mA.
,
10
3): Δ I
Inductors; V
MAX
L
= 227mA
because heavy load transients could
Output Current (mA)
IN
= 3.9V, V
100
OUT
17).
= 1.5V
MLP2520S1R5S
MLP2520S2R2S
MLP2520S3R3S
EPL2014-222
EPL2014-332
EPL2014-472
1000
21 - 24
(EQ 5)
(EQ 6)