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ISL8022

Dual 2A/1.7A Low Quiescent Current 2.25MHz High Efficiency Synchronous Buck Regulator

Renesas Electronics 

ISL8022

Thermal Shutdown

The ISL8022 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 ISL8022

resumes operation by stepping through a soft start-up.

Applications Information

Output Inductor and Capacitor Selection

To consider steady state and transient operation, ISL8022

typically uses a 1.2µH output inductor. 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.

The inductor ripple current can be expressed as in Equation 1:

I

=

V----O------------1-----–-----V-V------I--O--N------

L  fS

(EQ. 1)

The inductor’s saturation current rating needs to be at least

larger than the peak current. The ISL8022 protects the typical

peak current 3.2A/2.8A. The saturation current needs to be over

3.6A for maximum output current application.

ISL8022 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 for the ISL8022 on page 2.

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 “Typical Applications” on page 2 Figure 2.

The output voltage programming resistor, R2 (or R5 in Channel

2), will depend on the desired output voltage of the regulator. The

value for the feedback resistor is typically between 0 and

750k.

Let R3 = 100k, then R2 will be as shown in Equation 2:

R2

=

R3







V----O----U---T-

VFB

–



1



(EQ. 2)

If the output voltage desired is 0.6V, then R3 is left unpopulated

and short R2. For better performance, add 10pF in parallel to R2

Input Capacitor Selection

The main functions for the input capacitor is to provide

decoupling of the parasitic inductance and to provide filtering

function to prevent the switching current flowing back to the

battery rail. One 10µF X5R or X7R ceramic capacitor is a good

starting point for the input capacitor selection per channel. An

optional input inductor can be used before the ceramic capacitor

to limit switching noise. It is recommended to limit the

inductance less than 0.15µH.

PCB Layout Recommendation

The PCB layout is a very important converter design step to make

sure the designed converter works well. Refer to ISL8022 design

procedure for suggestions. For ISL8022, the power loop is

composed of the output inductor L’s, the output capacitor COUT1

and COUT2, the LX’s pins, and the GND 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

switching node of the converter, the LX_ pins, and the traces

connected to the node are very noisy, so keep the voltage

feedback trace away from these noisy traces. The input capacitor

should be placed to VIN pin as close as possible and the ground

of input and output capacitors should be connected as close as

possible. 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 better EMI performance. It is recommended to add at

least 5 vias ground connection within the pad for the best

thermal relief.

FN7650 Rev 3.00

March 14, 2013

Page 16 of 18

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