ISL8011 Ver la hoja de datos (PDF) - Renesas Electronics
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Fabricante
ISL8011 Datasheet PDF : 10 Pages
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ISL8011
a level that the ISL8011 can no longer maintain the regulation
at the output, the regulator completely turns on the P-
MOSFET. The maximum drop out voltage under the 100%
duty-cycle operation is the product of the load current and the
ON-resistance of the P-MOSFET.
Enable
The enable (EN) input allows user to control the turning on or
off the regulator for purposes such as power-up sequencing.
The the regulator is enabled, there is typically a 300µs delay
for waking up the bandgap reference. Then the soft start-up
begins. When the regulator is disabled, the P-MOSFET is
turned off immediately and the N-MOSFET is turned on.
Thermal Shut Down
The ISL8011 has built-in thermal protection. When the internal
temperature reaches +150°C, the regulator is completely shut
down. As the temperature drops to +130°C, the ISL8011
resumes operation by stepping through a soft start-up.
VCC By-Passing
The VCC is voltage is the supply to the internal control circuit
and is derived from the PVIN pin. An internal 5 resistor
connects the two pins and also serves as an filtering resistor.
An external 0.1µF ceramic capacitor is recommended to
by-pass the VCC supply.
Applications Information
Output Inductor and Capacitor Selection
To consider state steady and transient operation, ISL8011
typically uses a 1.8µH output inductor. Higher or lower inductor
values can be used to optimize the total converter system
performance. For example, for higher output voltage 3.3V
application, in order to decrease the inductor current ripple and
output voltage ripple, the output inductor value can be
increased as shown in Table 1. The inductor ripple current can
be expressed as shown in Equation 1:
I = V-----O--------L----1-----f–--S---V--V-------I--O--N-------
(EQ. 1)
The inductor’s saturation current rating needs be at least larger
than the peak current. The maximum peak current of ISL8011
is 2.1A. The saturation current needs be over 2.1A for
maximum output current application.
ISL8011 uses internal compensation network and the output
capacitor value is dependent on the output voltage. The
ceramic capacitor is recommended to be X5R or X7R. The
recommended minimum output capacitor values are shown in
Table 1.
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
VOUT
COUT
L
0.8V
10µF
1.0µH~2.2µH
FN9254 Rev 2.00
August 4, 2009
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
VOUT
1.2V
COUT
10µF
L
1.2µH~2.2µH
1.6V
10µF
1.8µH~2.2µH
1.8V
10µF
1.8µH~3.3µH
2.5V
10µF
1.8µH~3.3µH
3.3V
6.8µF
1.8µH~4.7µH
3.6V
4.7µF
1.8µH~4.7µH
In Table 1, the minimum output capacitor value is given for
different output voltage to make sure the whole converter
system stable. Due to the limitation on power dissipation when
the regulator disable and discharge output capacitor, there is
the maximum output capacitor value. The maximum output
capacitor value is variable with the output voltage. The plot
curve is shown in Figure 13.
600
505
410
315
220
125
30
0.8
1.27 1.73
2.2
2.67 3.13
3.6
OUTPUT VOLTAGE (V)
FIGURE 13. THE MAXIMUM CAP vs THE OUTPUT VOLTAGE
Input Capacitor Selection
The main functions for the input capacitor are to provide
decoupling of the parasitic inductance and to provide filtering
function to prevent the switching current flowing back to the
supply rail. A 10µF X5R or X7R ceramic capacitor is a good
starting point for the input capacitor selection.
Output Voltage Setting Resistor Selection
The resistors R2 and R3 shown in Figure 10 set the output
voltage for the adjustable version. The output voltage can be
calculated by using Equation 2:
VO
=
0.8
1
+
RR-----23-
(EQ. 2)
where the 0.8V is the reference voltage. To minimize the
accuracy impact on the output voltage, select the R2 and R3 no
larger than 100k.
Layout Recommendation
The layout is a very important converter design step to make
sure the designed converter works well. For ISL8011 buck
Page 8 of 10
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