AIC1550
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:
5. The FB pin should connect to feedback
resistors directly. And the route should be
away from the noise source, such as inductor
of LX line.
6. Grounding all components at the same point
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.
VD,MAX(OFF) = VIN
= IOUT,MAX
(5)
(6)
∆IL
+
ID,MAX(ON)
2
ID,AVG(ON) = IOUT −IIN = IOUT −D×IOUT
= (1−D)×IOUT
(7)
Adjustable Output Voltage
AIC1550 appears a 0.75V reference voltage at FB
pin. Output voltage, ranging from 0.75V to VIN,
can be set by connecting two external resistors,
R1 and R2. VOUT can be calculated as:
R1
Example
Here are two examples to prove the components
selector guide above.
1. Tantalum capacitors application:
VOUT = 0.75V × (1+
)
(8)
R2
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 VOUT=1.8V, VIN=4.2V,
∆I=250mA, and f=500KHz to equation (1)
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.
1.8V
1.8V
4.2V
Layout Consideration
L =
1−
= 8.23µH
500KHz × 250mA
To ensure a proper operation of AIC1550, the
following points should be given attention to:
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.
1. Input capacitor and Vin should be placed as
close as possible to each other to reduce the
input ripple voltage.
For output capacitor, the ESR is more important
than its capacity. Assuming ripple voltage
∆V=100mV, then the ESR can be calculated as:
∆V 100mV
2. The output loop, which is consisted of
inductor, Schottky diode and output capacitor,
should be kept as small as possible.
ESR=
=
= 0.4Ω
3. The routes with large current should be kept
short and wide.
∆I 250mA
Therefore, a 33µH/10V capacitor, MCM series
4. Logically the large current on the converter,
when AIC1550 is on or off, should flow at the
same direction.
from NIPPON, is recommend.
Schottky selection is calculated as following.
VD,MAX(OFF) = V = 4.2V
IN
12
AIC [ ANALOG INTERGRATIONS CORPORATION ]
