Microchip Technology MA330016 Data Sheet

DS70290J-page 14

© 2007-2011 Microchip Technology Inc.

2.2.1

TANK CAPACITORS

On boards with power traces running longer than six
inches in length, it is suggested to use a tank capacitor
for integrated circuits including DSCs to supply a local
power source. The value of the tank capacitor should
be determined based on the trace resistance that con-
nects the power supply source to the device, and the
maximum current drawn by the device in the applica-
tion. In other words, select the tank capacitor so that it
meets the acceptable voltage sag at the device. Typical
values range from 4.7 µF to 47 µF.

A low-ESR (< 5 Ohms) capacitor is required on the
V

CAP

 pin, which is used to stabilize the voltage

regulator output voltage. The V

CAP

 pin must not be

connected to V

DD

, and must have a capacitor between

4.7 µF and 10 µF, 16V connected to ground. The type
can be ceramic or tantalum. Refer to 

 for additional

information.

The placement of this capacitor should be close to the
V

CAP

. It is recommended that the trace length not

exceed one-quarter inch (6 mm). Refer to 

 for details.

The MCLR pin provides for two specific device
functions: 
• Device Reset
• Device programming and debugging 
During device programming and debugging, the
resistance and capacitance that can be added to the
pin must be considered. Device programmers and
debuggers drive the MCLR pin. Consequently,
specific voltage levels (V

IH

 and V

IL

) and fast signal

transitions must not be adversely affected. Therefore,
specific values of R and C will need to be adjusted
based on the application and PCB requirements.
For example, as shown in 

, it is

recommended that capacitor C is isolated from the
MCLR pin during programming and debugging
operations.
Place the components shown in 

 within

one-quarter inch (6 mm) from the MCLR pin.

V

DD

V

SS

V

DD

V

SS

V

SS

V

DD

AV

DD

AV

SS

V

DD

V

SS

0.1 µF

Ceramic

0.1 µF

Ceramic

0.1 µF

Ceramic

0.1 µF

Ceramic

C

R

V

DD

MCLR

0.1 µF

Ceramic

V

CA

P

L1

R1

10 µF

Tantalum

As an option, instead of a hard-wired connection, an
inductor (L1) can be substituted between V

DD

 and

AV

DD

 to improve ADC noise rejection. The inductor

impedance should be less than 1

Ω and the inductor

capacity greater than 10 mA.

Where:

2

--------------

=

1

2

π LC

(

)

-----------------------

=

1

2

πf C

(

)

---------------------

⎝

⎠

⎛

⎞

2

=

(i.e., ADC conversion rate/2)

Note 1: R

≤ 10 kΩ is recommended. A suggested

starting value is 10 k

Ω. Ensure that the MCLR

pin V

IH

 and V

IL

 specifications are met.

2: R1

≤ 470Ω will limit any current flowing into

MCLR from the external capacitor C, in the
event of MCLR pin breakdown, due to
Electrostatic Discharge (ESD) or Electrical
Overstress (EOS). Ensure that the MCLR pin
V

IH

 and V

IL

 specifications are met.

C

R1

R

V

DD

MCLR

JP