LM2940CT-9.0 National Semiconductor, LM2940CT-9.0 Datasheet - Page 10

• Manufacturer Part Number: LM2940CT-9.0
• Description: IC,VOLT REGULATOR,FIXED,+9V,BIPOLAR,SIP,3PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM2940CT-9.0

• Rohs Compliant: NO

www.national.com
Equivalent Schematic Diagram
Application Hints
EXTERNAL CAPACITORS
The output capacitor is critical to maintaining regulator stabil-
ity, and must meet the required conditions for both ESR
(Equivalent Series Resistance) and minimum amount of ca-
pacitance.
MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain stabil-
ity is 22 µF (this value may be increased without limit).
Larger values of output capacitance will give improved tran-
sient response.
ESR LIMITS:
The ESR of the output capacitor will cause loop instability if
it is too high or too low. The acceptable range of ESR plotted
versus load current is shown in the graph below. It is essen-
tial that the output capacitor meet these requirements,
or oscillations can result.
10
It is important to note that for most capacitors, ESR is speci-
fied only at room temperature. However, the designer must
ensure that the ESR will stay inside the limits shown over the
entire operating temperature range for the design.
For aluminum electrolytic capacitors, ESR will increase by
about 30X as the temperature is reduced from 25˚C to
−40˚C. This type of capacitor is not well-suited for low tem-
perature operation.
Solid tantalum capacitors have a more stable ESR over tem-
perature, but are more expensive than aluminum electrolyt-
ics. A cost-effective approach sometimes used is to parallel
Output Capacitor ESR
FIGURE 1. ESR Limits
DS008822-6
DS008822-1