isl9106 Intersil Corporation, isl9106 Datasheet - Page 12

• Manufacturer Part Number: isl9106
• Description: 1.2a 1.6mhz Low Quiescent Current High Efficiency Synchronous Buck Regulator
• Manufacturer: Intersil Corporation

Input Capacitor Selection
The main function for the input capacitor is to provide
decoupling of the parasitic inductance and to provide filtering
function to prevent the switching current from flowing back to
the battery rail. A 10μF/6.3V ceramic capacitor (X5R or X7R)
is a good starting point for the input capacitor selection.
Output Voltage Setting Resistor Selection
The voltage divider resistors, R
23, set the desired output voltage value. The output voltage
can be calculated using Equation 2:
where V
current flowing through the voltage divider resistors can be
calculated as V
to minimize this current. On the other hand, the FB pin has
leakage current that will cause error in the output voltage
setting. The leakage current has a typical value of 0.1μA. To
minimize the accuracy impact on the output voltage, select
the R
C
for improving stability and achieving better transient
response. C
Table 1 provides the recommended component values for
some output voltage options.
Layout Recommendation
The PCB layout is a very important converter design step to
make sure the designed converter works well, especially
under the high current high switching frequency condition.
For ISL9106, the power loop is composed of the output
inductor L, the output capacitor C
PGND pin. It is necessary to make the power loop as small
as possible and the connecting traces among them should
be direct, short and wide; the same type of traces should be
used to connect the VIN pin, the input capacitor C
ground. In order to make the output voltage regulate well
and avoid the noise couple from the power loop (especially
for SKIP mode operation), the SGND pin should be
connected with the PGND pin at the terminals of the load
and a star ground connection should be used.
V
C
O
3
3
(shown in Figure 23) is highly recommended to be added
=
=
3
V
---------------------------------------------------- -
2
no larger than 200kΩ.
FB
×
FB
π
•
×
is the feedback voltage (typically it is 0.8V). The
⎛
⎜
⎝
3
R
1
can be calculated using Equation 3:
2
+
1
O
×
R
------ -
R
/(R
7.3kHz
2
3
⎞
⎟
⎠
2
+ R
3
), so larger resistance is desirable
12
2
and R
OUT
, the SW pin and the
3
, as shown in Figure
IN
and its
(EQ. 2)
(EQ. 3)
ISL9106
The switching node of the converter, the SW pin, and the
traces connected to this node are very noisy, so keep the
voltage feedback trace and other noise sensitive traces
away from these noisy traces.
The input capacitor should be placed as close as possible to
the VIN pin. The ground of the input and output capacitors
should be connected as close as possible as well.
The heat of the IC is mainly dissipated through the thermal
pad. Maximizing the copper area connected to the thermal
pad is preferable. In addition, a solid ground plane is helpful
for EMI performance.
VOUT (V)
0.8
1.0
1.2
1.5
1.8
2.5
2.8
3.3
TABLE 1. ISL9106 CIRCUIT CONFIGURATION vs V
L (μH)
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
C2 (μF)
10
10
10
10
10
10
10
10
R2 (kΩ)
44.2
80.6
84.5
100
100
100
102
0
C3 (pF)
N/A
470
270
270
220
220
220
220
June 29, 2007
R3 (kΩ)
OUT
97.6
80.6
47.5
40.2
32.4
FN6509.0
100
178
162