Acutechnology Semiconductor Inc.
SELECTION OF PNP PASS DEVICE
AQ120
In the application of (figure 1) above, an FMMT549 SOT223 package was used.
However, selection of the PNP pass device is based on Vin max, Iout max, and Power dissipation for
your particular application.
V
IN
max
BVCEO and BVCBO minimum rating of the PNP transistor must exceed the maximum Vin of the
application. The AQ120 will stand off 18V max. Therefore the maximum voltage the PNP will
experience is 18V.
Iout max
Beta of the PNP transistor will dictate the maximum output current as per the equation:
Iout
max
=
Idrive
max(20
mA
)
∗
BetaExt
.
PNP
Higher beta of the PNP will improve the Vout variation due to change in load (load reg.) Minimizing the
Idrive required will also minimize the Load reg. as Vout will decrease by .15% per mA of Idrive.
Therefore, delta 10mA of Idrive will cause a delta 1.5% of Vout.
Power dissipation
Selection of the external PNP package is based on size requirements and power dissipation. Consult
the transistor data sheet for power considerations.
Contact Information
Acutechnology Semiconductor Inc.
3487 McKee Rd. Suite 52
San Jose CA , USA 95127
Disclaimer
The information furnished by Acutechnology in this data sheet is believed to be accurate and reliable. However,
Acutechnology assumes no responsibility for its use. Acutechnology reserves the right to change circuitry and specifications
at any time without notification to the customer.
TEL:
FAX:
website:
(408) 259-2300
(408) 259-9160
www.acutechnology.com
Life Support Policy
Acutechnology Products are not designed or authorized for use as components in life support devices or systems where
malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are
devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to
perform can be reasonably expected to result in a significant injury to the user.
www.acutechnology.com
5
Rev. 1.2
April 1, 2006
ACUTECH [ ACUTECHNOLOGY SEMICONDUCTOR ]
