ML4865 Просмотр технического описания (PDF) - Micro Linear Corporation

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ML4865

High Voltage High Current Boost Regulator

Micro Linear Corporation 

ML4865

DESIGN CONSIDERATIONS (Continued)

SHUTDOWN

The SHDN pin is a high impedance input and is noise

sensitive. Either drive the SHDN input from a low

impedance source or bypass the pin to GND with a 10nF

ceramic capacitor.

SENSE

The SENSE pin should be left open or bypassed to ground

for normal operation. The output can be set to voltages

lower than the preset value by adding a resistor divider.

The output voltage can be determined from the following

equation:

VOUT

= 2.42 ´ R1+ R2

R2

(V)

(3)

where R1 and R2 are connected as shown in Figure 2. The

value of R2 should be 1MW or less to minimize bias

current errors. Choose an appropriate value of R2 and

calculate the value of R1.

  R1= R2´

VOUT

2.42

-1

(W)

(4)

EXTERNAL SCHOTTKY RECTIFIER

Due to excessive power dissipation, an external Schottky

rectifier is required when operating at input voltages

above 6V. Even for applications where the input voltage is

below 6V, the use of an external rectifier may be

necessary to achive efficiency or output current

requirements.

If an external Schottky is required, look for a device with

a voltage rating of 20V or greater. The average forward

current rating should be at least 500mA, and the forward

voltage should be 600mV or less. Suitable Schottky

rectifiers can be obtained from the following vendors:

Diodes, Inc B120

(805) 446-4800

Int’l Rectifier 10BQ040

(310) 322-3331

Motorola MBR0520L (602) 897-5056

LAYOUT

Good layout practices will ensure the proper operation of

the ML4865. Some layout guidelines follow:

• Use adequate ground and power traces or planes

• Keep components as close as possible to the ML4865

• Use short trace lengths from the inductor to the VL1 and

VL2 pins and from the output capacitor to the VOUT pin

• Use a single point ground for the ML4865 ground pin,

and the input and output capacitors

• Separate the ground for the converter circuitry from the

ground of the load circuitry and connect at a single

point

A sample layout is shown in Figure 8.

Figure 8. Sample ML4865 Layout

8

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