AIC1550 AIC [Analog Intergrations Corporation], AIC1550 Datasheet - Page 12

• Manufacturer Part Number: AIC1550
• Description: Low-Noise Synchronous PWM Step-Down DC/DC Converter
• Manufacturer: AIC [Analog Intergrations Corporation]

Since the diode conducts during the off time, the
peak current and voltage of converter is not
allowed to exceed the diode ratings. The ratings
of diode can be calculated by the following
formulas:
Adjustable Output Voltage
AIC1550 appears a 0.75V reference voltage at FB
pin. Output voltage, ranging from 0.75V to V
can be set by connecting two external resistors,
R1 and R2. V
Applying a 12pF capacitor parallel with R1 can
prevent stray pickup. They should sit as close to
AIC1550 as possible. But load transient response
is degraded by this capacitor.
Layout Consideration
To ensure a proper operation of AIC1550, the
following points should be given attention to:
I
I
V
V
, D
1. Input capacitor and Vin should be placed as
2. The output loop, which is consisted of
3. The routes with large current should be kept
4. Logically the large current on the converter,
, D
OUT
, D
MAX
AVG
MAX
close as possible to each other to reduce the
input ripple voltage.
inductor, Schottky diode and output capacitor,
should be kept as small as possible.
short and wide.
when AIC1550 is on or off, should flow at the
same direction.
(
(
=
ON
ON
(
OFF
. 0
)
)
75
)
=
=
=
=
V
I
I
(1
OUT
OUT
OUT
V
×
−
IN
1 (
D)
,
MAX
can be calculated as:
+
−
I
×
R
R
IN
I
2
OUT
1
+
=
)
∆
I
OUT
2
I
L
−
D
×
I
OUT
(5)
(6)
(7)
(8)
IN
,
Example
Here are two examples to prove the components
selector guide above.
1. Tantalum capacitors application:
Assume AIC1550 is used for mobile phone
application, which uses 1-cell Li-ion battery with
2.7V to 4.2V input voltage for power source. The
required load current is 800mA, and the output
voltage is 1.8V. Substituting V
∆I=250mA, and f=500KHz to equation (1)
Therefore, 10µH is proper for the inductor. And
the inductor of series number SLF6025-100M1R0
from TDK with 57.3mΩ series resistor is
recommended for the best efficiency.
For output capacitor, the ESR is more important
than
∆V=100mV, then the ESR can be calculated as:
Therefore, a 33µH/10V capacitor, MCM series
from NIPPON, is recommend.
Schottky selection is calculated as following.
L
V
5. The FB pin should connect to feedback
6. Grounding all components at the same point
, D
=
MAX
500
resistors directly. And the route should be
away from the noise source, such as inductor
of LX line.
may effectively reduce the occurrence of loop.
A stability ground plane is very important for
gaining higher efficiency. When a ground
plane is cut apart, it may cause disturbed
signal and noise. If possible, two or three
through-holes can ensure the stability of
grounding. Fig.24 to 27 show the layout
diagrams of AIC1550.
its
ESR
(
OFF
KHz
1
)
capacity.
=
8 .
=
×
∆
V
∆
V
250
V
I
IN
=
mA
=
100
250
4
2 .



Assuming
mV
1
mA
V
−
1
4
=
8 .
2 .
0
V
V
OUT
4 .



Ω
=
=1.8V, V
AIC1550
ripple
. 8
23
µ
H
IN
voltage
=4.2V,
12