AS1324 AMSCO [austriamicrosystems AG], AS1324 Datasheet - Page 15

• 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
Basic losses in the design of a system should also be considered. Internal battery resistances and copper trace can
account for additional efficiency degradations in battery operated systems. By making sure that C
charge storage and very low ESR at the given switching frequency, the internal battery and fuse resistance losses can
be minimized. C
additional loss.
Thermal Shutdown
Due to its high-efficiency design, the AS1324 will not dissipate much heat in most applications. However, in applica-
tions where the AS1324 is running at high ambient temperature, uses a low supply voltage, and runs with high duty
cycles (such as in dropout) the heat dissipated may exceed the maximum junction temperature of the device.
As soon as the junction temperature reaches approximately 150ºC the AS1324 goes in thermal shutdown. In this mode
the internal PMOS & NMOS switch are turned off. The device will power up again, as soon as the temperature falls
below +145°C again.
Checking Transient Response
The main loop response can be evaluated by examining the load transient response. Switching regulators normally
take several cycles to respond to a step in load current. When a load step occurs, V
amount equivalent to:
Where:
ESR is the effective series resistance of C
Δ I
to return V
would indicate a stability problem.
Design Example
Figure 28
load current requirement is 600mA (max) but most of the time the device will require only 2mA (standby mode current).
Figure 28. Design Example
For the circuit shown in
ing the value for the external inductor, which is calculated as:
From
Therefore, a standard 2.2µH inductor should be used for this design.
www.austriamicrosystems.com
OUT
(EQ
also begins to charge or discharge C
shows the AS1324 used in a single lithium-ion (3.7V typ) battery-powered mobile phone application. The
OUT
14), substituting V
to its steady-state value. During this recovery time V
3.7V
V
IN
IN
and C
Figure
OUT
4.7µF
CER
C
IN
OUT
ESR dissipative losses and inductor core losses generally account for less than 2% total
28, efficiency at low- and high-load currents is an important consideration when select-
= 2.2V, V
L
=
--------------------------------------------------- -
(
1,5MHz 240mA
V
EN
IN
OUT
4
1
IN
OUT
V
= 3.7V, Δ I
DROP
.
, which generates a feedback error signal. The regulator loop then acts
L
2,2V
AS1324
×
=
2
= ΔI
V
--------------
f Δ I
Revision 1.03
OUT
GND
L
OUT
L
= 240mA and f = 1.5MHz gives:
×
)
x ESR
⎛
⎝
×
1
3
SW
5
V
⎛
⎝
–
1
FB
R
V
--------------
1
–
V
OUT
2,2V
------------
3 7V
IN
OUT
,
375kΩ
2.2µH
⎞
⎠
⎞
⎠
can be monitored for overshoot or ringing that
22pF
1MΩ
R
=
2
2,48 μ H
OUT
C
10µF
immediately shifts by an
CER
OUT
V
2.2V
IN
OUT
has adequate
(EQ 13)
(EQ 14)
(EQ 15)
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