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5

HEATSINKING

The PA79DK package has a large exposed integrated copper

heatslug to which the monolithic amplifier is directly attached.

The solder connection of the heat slug to a 1 square inch foil

area on the printed circuit board will result in improved ther-

mal performance of 25C/W. In order to improve the thermal

performance, multiple metal layers in the printed circuit board

are recommended. This may be adequate heatsinking but

the large number of variables involved suggest temperature

measurements be made on the top of the package. Do not

allow the temperature to exceed 85°C.

The junction to ambient thermal resistance of the DK pack-

age can achieve a 19.1C/W rating by using the PCB conditions

outlined in JEDEC standard: (JESD51–5):

PCB Conditions:

PCB Layers = 4L, Copper, FR–4

PCB Dimensions = 101.6 x 114.3mm

PCB Thickness = 1.6mm

Conditions:

Power dissipation = 2 watt

Ambient Temperature = 55°C

STABILITY

The PA79 is externally compensated and performance can

be tailored to the application. Use the graphs of small signal

response and power response as a guide. Due to the innovative

design of the PA79, two compensation networks are required.

The values of these components should be the same to pro-

vide symmetric slew rate characteristics. The compensation

capacitor Cc must be rated at 500V working voltage. NPO

capacitors are recommended. The compensation networks

CcRc must be mounted closely to the amplifier pins 8 & 11

and 3 & 10 to avoid spurious oscillation.

The PA79 may require an external 33 pF capacitor (mini-

mum breakdown of 350V) between Cc– and –Vs to prevent

oscillations in the falling edge of the output. This capacitor

is provided with the evaluation kit. Please refer to EK60U

datasheet for details.

ELECTROSTATIC DISCHARGE

Like many high performance MOSFET amplifiers, the PA79

very sensitive to damage due to electrostatic discharge (ESD).

Failure to follow proper ESD handling procedures could have

results ranging from reduced operating performance to cata-

strophic damage. Minimum proper handling includes the use

of grounded wrist or shoe straps, grounded work surfaces.

Ionizers directed at the work in progress can neutralize the

charge build up in the work environment and are strongly

recommended.

GENERAL

Please read Application Note 1 “General Operating Consid-

erations” which covers stability, power supplies, heat sinking,

mounting, current limit, SOA interpretation, and specification

interpretation. Visit www.apexmicrotech.com for design tools

that help automate tasks such as calculations for stability,

internal power dissipation, current limit, heat sink selection,

Apex’s complete Application Notes library, Technical Seminar

Workbook and Evaluation Kits.

SPECIAL CONSIDERATIONS

It is very important to realize that in order to achieve

high frequency performance the heat sink tab has to be

tied to a stable, low impedance reference, i.e. power sup-

ply or GND. An AC connection through a 0.1µF capacitor

is also sufficient. Internal to the PA79, the heatsink tab

is electrically isolated to more than 350V . This may help

allay some electrical isolation concerns in tying the heat

sink to Vs or GND.

CURRENT LIMIT

For proper operation, the current limit resistor, R

be connected as shown in the external connections diagram.

For maximum reliability and protection, the resistor should be

set as high as possible. The maximum practical value using

the following formula is 12 ohms. For even lower current limit

values, please see the CURRENT LIMIT vs. RESISTOR graph

on the TYPICAL PERFORMANCE GRAPHS page.

R

POWER SUPPLY BYPASSING

Bypass capacitors to power supply terminals +Vs and –Vs

must be connected physically close to the pins to prevent local

parasitic oscillation in the output stage of the PA79. Use high

quality ceramic capacitors (X7R) 0.1μF or greater.

SUPPLY CURRENT

The PA79 features a class A/B driver stage to drive the output

MOSFETs and an innovative input stage to achieve very high

slew rates. The supply current drawn by the PA79, even with

no load, varies with the slew rate of the output signal.

MOISTURE SENSITIVITY

The PA79DK has been qualified according to JEDEC 22-A-

113-D, MSL 3. The following conditions were used: IR reflow

for Pb-free assembly profile where: package thickness is

TP = 245°C.

OPERATING

CONSIDERATIONS

This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.

PA79U REV A1 JULY 2007 © 2007 Apex Microtechnology Corp.

PA79