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FN6309.3
November 23, 2009
For additional products, see www.intersil.com/product_tree
Power MOSFETs
The power MOSFETs are optimized for best efficiency.
The ON-resistance for the P-MOSFET is typically 50mΩ
and the ON-resistance for the N-MOSFET is typically
50mΩ.
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 oper ation 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 reach es +140°C, the regulator is
completely shut down. As the temperature drops to
+115°C, the ISL8013 resumes operation by stepping
through the soft-start.
Applications Information
Output Inductor and Capacitor Selection
To consider steady state and tr ansient oper ations,
ISL8013 typically uses a 1.5µH output inductor. The
higher or lower inductor v alue 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 v alue 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:
The inductor’s satur ation current r ating needs to be at
least larger than the peak current. The ISL8013 protects
the typical peak current 4.8A. The satur ation current
needs be over 5.5A for maximum output current
application.
ISL8013 uses internal compensation network and the
output capacitor value is dependen t 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.
In Table 1, the minimum output capacitor value is given
for the different output voltage to mak e sure that th e
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 progr ammed
via an external resistor divider that is used to scale the
output voltage relativ e to the internal reference v oltage
and feed it back to the inverting input of the error
amplifier. Refer to Figure 1.
The output voltage programming resistor, R3, will depend
on the value chosen for the feedback resistor and the
desired output voltage of the regulator. The value for the
feedback resistor is typically between 10kΩ and 100kΩ,
as shown in Equation 4.
If the output voltage desired is 0.8V, then R3 is left
unpopulated and R2 is shorted. There is a leakage
current from VIN to LX. It is recommended to preload the
output with 10µA minimum. F or better performance, add
47pF in parallel with R2 (100kΩ).
Input Capacitor Selection
The main functions for the input capacitor are to provide
decoupling of the parasitic inductance and to pro vide
filtering function to prevent the switching current flowing
back to the battery r ail. Two 22µF X5R or X7R cer amic
capacitors are a good starting point for the input
capacitor selection.
ΔI
VO1VO
VIN
---------
–
⎝⎠
⎜⎟
⎛⎞
⋅
Lf
S
⋅
-------------------------------------
=
(EQ. 3)
TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT
VOUT (V) COUT (µF) L (µH)
0.8 2 x 22 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
R3R20.8V⋅
VOUT 0.8V–
----------------------------------=(EQ. 4)
ISL8013