ISL8014IRZ datasheet(14/17 Pages) RENESAS

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ISL8014

FN6576 Rev 4.00

Page 14 of 17

November 23, 2009

Thermal Shut-Down

The ISL8014 has built-in thermal protection. When the

internal temperature reaches +140°C, the regulator is

completely shut down. As the temperature drops to

+115°C, the ISL8014 resumes operation by stepping

through the soft-start.

Applications Information

Output Inductor and Capacitor Selection

To consider steady state and transient operations,

ISL8014 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:

The inductor’s saturation current rating needs to be at

least larger than the peak current. The ISL8014 protects

the typical peak current 6A. The saturation current needs

be over 7A for maximum output current application.

ISL8014 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.

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.

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 10k and 100k

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. For better performance, add

47pF in parallel with R2 (100k

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 battery rail. Two 22µF X5R or X7R ceramic

capacitors are a good starting point for the input

capacitor selection.

TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT

VOUT

(V)

COUT

(µF)

(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

I

VO 1

VIN

---------

–









LfS



-------------------------------------

(EQ. 3)

R2 0.8V



VOUT 0.8V

–

----------------------------------

(EQ. 4)

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