P r o d u c t I n n o v a t i o n F r o m

MP400

MP400U

11

layoUt consiDerations

The PA78 is built on a dielectrically isolated process and the package tab is therefore not electrically connected

to the amplifier. For high speed operation, the package tab should be connected to a stable reference to reduce

capacitive coupling between amplifier nodes and the floating tab. It is often convenient to directly connect the tab

to GND or one of the supply rails, but an AC connection through a 1µF capacitor to GND is also sufficient if a DC

connection is undesirable

Care should be taken to position the R

to the amplifier compensation pins. Long loops in these paths pick up noise

and increase the likelihood of LC interactions and oscillations.

sMPs oPeration

The MP400FC is designed to operate off of a standard voltage rail. Typi-

cal values include 12 V, 24 V, or 48 V. The addition of the on-board SMPS

eliminates the need to design or purchase a high voltage power supply. The

only inputs required by the SMPS are the V

capacitor, and boost voltage set resistor (R

The SMPS output can be adjusted between a minimum of 50 V to a max-

imum of 350 V. The voltage boost adjustment is independent of V

justment to the boost level is made through a resistor from the R

ground. The resistor value is:

Where V

Example:

1) Desired V

2) R

If R

Note that while the MP400 SMPS generates a positive voltage from 50 V to 350 V, the amplifier may operate from

a variety of supply voltages. Symmetric, asymmetrical and single supply configurations can be used so long as the

total supply voltage from +V

include some plots taken with symmetrical supplies, but those plots generally apply to all supply configurations.

sMPs oUtPUt caPacitor

An external SMPS output filter capacitor is required for proper operation. ESR considerations prevail in the choice

of the output filter capacitor. Select the highest value capacitor that meets the following ESR requirement. The

minimum value for C

ESR = dVo/I

LPK

Where,

dVo

= The maximum acceptable output ripple voltage

I

LPK

= Peak inductor current = (1/L) • V

L

V

IN

= Input voltage of the application.

ton

= √(2 • Io • L • ((Vo + 0.6 - V

2

)))

V

BOOST

= The boost supply voltage of the application.

I

O

= The maximum continuous output current for the application.

F

SW

= 100 KHz switching frequency of the MP400FC boost supply.

SMPS Output vs. RSET

1

10

100

1000

10000

100000

VBoost (V)

50

100 150 200 250 300 350

R

- 615

V