ISL8013 Ver la hoja de datos (PDF) - Renesas Electronics
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ISL8013 Datasheet PDF : 18 Pages
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ISL8013
Figures 38 and 39 for suggested circuit implementation
with VIN slew rate.
VIN
2.5V
EN
<400mV
T
t (TIME)
FIGURE 39. CIRCUIT IMPLEMENTATION WITH VIN
SLEW RATE
Let T equal the rise time of VIN. Select the ratio of R5 and
R4 such that the voltage is 1.4V (minimum enable logic
high threshold) when VIN is equal to or greater than
2.5V. Set R5 between 10k to 100k, and use Equation 1
to determine R4:
R4 = -R----5----------V--1--I-.-N-4----V–-----1---.--4----V----
(EQ. 1)
Where VIN is greater than or equal to 2.5V.
Then select C such that the equivalent time constant is at
least 2x the rise time, T. This will delay the EN voltage
enough so that the overall EN voltage is less than 400mV
by the time VIN reaches 2.5V. Use Equation 2 to get C:
C R----2-4--------TR-----5-
(EQ. 2)
Where T is the rise time of VIN
As an example, let VIN = 5V with rise time, T = 10ms.
Then R4 = 56.2k, R5 = 71.5k, and C = 0.68µF are
used to insure that VIN was >2.5V and the EN voltage
was <400mV.
Discharge Mode (Soft-Stop)
When a transition to shutdown mode occurs or the VIN
UVLO is set, the outputs discharge to GND through an
internal 100 switch.
Power MOSFETs
The power MOSFETs are optimized for best efficiency.
The ON-resistance for the P-MOSFET is typically 50m
and the ON-resistance for the N-MOSFET is typically
50m.
100% Duty Cycle
The ISL8013 features 100% duty cycle operation to
maximize the battery life. When the battery voltage
drops to a level that the ISL8013 can no longer maintain
the regulation at the output, the regulator completely
turns on the P-MOSFET. The maximum dropout voltage
under the 100% duty-cycle operation is the product of
the load current and the ON-resistance of the P-MOSFET.
Thermal Shut-Down
The ISL8013 has built-in thermal protection. When the
internal temperature reaches +140°C, the regulator is
completely shut down. As the temperature drops to
FN6309 Rev 3.00
November 23, 2009
+115°C, the ISL8013 resumes operation by stepping
through the soft-start.
Applications Information
Output Inductor and Capacitor Selection
To consider steady state and transient operations,
ISL8013 typically uses a 1.5µH output inductor. The
higher or lower inductor value 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. It is
recommended to set the ripple inductor current
approximately 30% of the maximum output current for
optimized performance. The inductor ripple current can
be expressed as shown in Equation 3:
I = V-----O--------L---1-----f–--S---V-V--------I--O--N-------
(EQ. 3)
The inductor’s saturation current rating needs to be at
least larger than the peak current. The ISL8013 protects
the typical peak current 4.8A. The saturation current
needs be over 5.5A for maximum output current
application.
ISL8013 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 X5R or X7R minimum
output capacitor values are shown in Table 1.
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
VOUT (V)
0.8
COUT (µF)
2 x 22
L (µH)
1.0~2.2
1.2
2 x 22
1.0~2.2
1.5
2 x 22
1.5~3.3
1.8
2 x 22
1.5~3.3
2.5
2 x 22
1.5~3.3
3.3
2 x 22
2.2~4.7
3.6
2 x 22
2.2~4.7
In Table 1, the minimum output capacitor value is given
for the different output voltage to make sure that the
whole converter system is stable. Additional output
capacitance should be added for better performances in
applications where high load transient or low output
ripple is required. It is recommended to check the
system level performance along with the simulation
model.
Output Voltage Selection
The output voltage of the regulator can be programmed
via an external resistor divider that is used to scale the
output voltage relative to the internal reference voltage
and feed it back to the inverting input of the error
amplifier. Refer to Figure 1.
Page 15 of 18
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