MCP6541 datasheet(13/28 Pages) MICROCHIP

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 2003 Microchip Technology Inc.

DS21696C-page 13

MCP6541/2/3/4

Where:

Using this simplified circuit, the trip voltage can be

calculated using the following equation:

EQUATION

Figure 2-19 and Figure 2-22 can be used to determine

typical values for VOH and VOL.

3.5

Bypass Capacitors

With this family of comparators, the power supply pin

(VDD for single supply) should have a local bypass

capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm for good

edge rate performance.

3.6

Capacitive Loads

Reasonable capacitive loads (e.g., logic gates) have

little impact on propagation delay (see Figure 2-27).

The supply current increases with increasing toggle

frequency

(Figure 2-30),

especially

with

higher

capacitive loads.

3.7

Battery Life

In order to maximize battery life in portable

applications, use large resistors and small capacitive

loads. Also, avoid toggling the output more than

necessary and do not use chip select (CS) to conserve

power for short periods of time. Capacitive loads will

draw additional power at start-up.

3.8

PCB Surface Leakage

In applications where low input bias current is critical,

PCB (Printed Circuit Board) surface leakage effects

need to be considered. Surface leakage is caused by

humidity, dust or other contamination on the board.

Under low humidity conditions, a typical resistance

between nearby traces is 1012

Ω. A 5V difference would

cause 5 pA, if current-to-flow. This is greater than the

MCP6541/2/3/4 family’s bias current at 25°C (1 pA,

typ).

The easiest way to reduce surface leakage is to use a

guard ring around sensitive pins (or traces). The guard

ring is biased at the same voltage as the sensitive pin.

An example of this type of layout is shown in

Figure 3-8.

FIGURE 3-8:

Example Guard Ring Layout

for Inverting Circuit.

Inverting Configuration (Figures 3-5 and 3-8):

Connect the guard ring to the non-inverting

input pin (VIN+). This biases the guard ring

to the same reference voltage as the

comparator (e.g., VDD/2 or ground).

Connect the inverting pin (VIN–) to the input

pad without touching the guard ring.

Non-inverting Configuration (Figure 3-3):

Connect the non-inverting pin (VIN+) to the

input pad without touching the guard ring.

Connect the guard ring to the inverting input

pin (VIN–).

R23

R2R3

R2 R3

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

V23

R2 R3

------------------ V

VTHL

VOH

R23

R23 RF

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







V23

R23 RF

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





VTLH

VOL

R23

R23 RF

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







V23

R23 RF

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





VTLH = trip voltage from low to high

VTHL = trip voltage from high to low

Guard Ring

VIN-VIN+

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