Microchip Technology MA330019 데이터 시트

DS70291G-page  18

© 2007-2012 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 
connects the power supply source to the device, and 
the maximum current drawn by the device in the 
application. 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, preferably surface mount connected 
within one-eights inch of the V

CAP

 pin 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 the capacitor C be 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

CAP

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