ML4861 Ver la hoja de datos (PDF) - Micro Linear Corporation

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componentes Descripción

Fabricante

ML4861

Low Voltage Boost Regulator

Micro Linear Corporation 

ML4861

INPUT CAPACITOR

Unless the input source is a very low impedance battery, it

will be necessary to decouple the input with a capacitor

with a value of between 47µF and 100µF. This provides

the benefits of preventing input ripple from affecting the

ML4861 control circuitry, and it also improves efficiency

by reducing I-squared R losses during the charge and

discharge cycles of the inductor. Again, a low ESR

capacitor (such as tantalum) is recommended.

REFERENCE CAPACITOR

Under some circumstances input ripple cannot be

reduced effectively. This occurs primarily in applications

where inductor currents are high, causing excess output

ripple due to “pulse grouping”, where the charge-

discharge pulses are not evenly spaced in time. In such

cases it may be necessary to decouple the reference pin

(VREF) with a small 10nF to 100nF ceramic capacitor. This

is particularly true if the ripple voltage at VIN is greater

than 100mV.

SETTING THE RESET THRESHOLD

To use the RESET comparator as an input voltage monitor,

it is necessary to use an external resistor divider tied to the

DETECT pin as shown in the block diagram. The resistor

values RA and RB can be calculated using the following

equation:

VIN(MIN)

=

0.2

×

(RA + RB)

RB

(5)

The value of RB should be 100ký or less to minimize bias

current errors. RA is then found by rearranging the

equation:

RA

= RB

×





VIN(MIN)

0.2



− 1

(6)

LAYOUT

Good PC board layout practices will ensure the proper

operation of the ML4861. Important layout considerations

include:

• Use adequate ground and power traces or planes

• Keep components as close as possible to the ML4861

• Use short trace lengths from the inductor to the VL pin

and from the output capacitor to the VOUT pin

• Use a single point ground for the ML4861 ground pins,

and the input and output capacitors

A sample PC board layout is shown in Figure 6.

TOP LAYER

BOTTOM LAYER

Figure 6. Sample PC Board Layout.

8

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