Microchip Technology MA330031-2 Data Sheet

DS70000657H-page 30

 2011-2013 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 (< 1 Ohm) 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 greater than 4.7 µF

(10 µF is recommended), 16V connected to ground. The
type can be ceramic or tantalum. See 

 for additional information.

The placement of this capacitor should be close to the
V

CAP

 pin. It is recommended that the trace length not

exceeds one-quarter inch (6 mm). See 

 for details.

The MCLR pin provides 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 the capacitor, C, be isolated from the MCLR pin
during programming and debugging operations.
Place the components as 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

 and the inductor 

capacity greater than 10 mA.

Where:

2

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

=

1

2

 LC





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

=

1

2

f C





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









2

=

(i.e., ADC conversion rate/2)

R

 10 k is recommended. A suggested 

starting value is 10 k

. Ensure that the MCLR 

pin V

IH

 and V

IL

 specifications are met.

R1

 470 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