AS3682 datasheet(37/43 Pages) AMSCO

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AS3682

austriamicrosystems

Data Sheet

Capacitor and Resistor Selection

www.austriamicrosystems.com

Revision 2.21

37 - 43

12 External Components

12.1 Capacitor and Resistor Selection

Use low-ESR ceramic capacitors with X7R or X5R dielectric – these capacitors allow good filtering and have a wide

temperature range. The connections of all external capacitors should be kept as short as possible.

All resistors should have a tolerance of ±1%.

12.2 Usage of PCB Wire Inductance

The inductance between the battery and pins VBAT1 and VBAT2 can be used as a filter to reduce disturbance on the bat-

tery. Instead of using one capacitor (C1) it is recommended to split C1 into C11 and C12 with the capacitance equal:

C11 = C12 = 1/2 x C1

(EQ 1)

It is recommended to apply a minimum of 20nH (maximum 200nH) with low impedance. This inductance can be real-

ized on the PCB without any discrete coil. Assuming that 1mm signal line corresponds to approximately 1nH (valid if

the length (L) is significantly bigger than the width (W) of the line (L/W <10)). Thus a line length of:

20mm < L < 200mm

(EQ 2)

is recommended. The shape of the line is not important.

Figure 24. PCB Wire Inductance Example 1

Figure 25. PCB Wire Inductance Example 2

12.3 External Component Specifications

Notes:

1. See Usage of PCB Wire Inductance on page 37.

Table 39. External Components List

Part

Number

Value

Tol

(Min)

Rating

(Max)

Notes

Package

(Min)

Min

Typ

Max

C11

2.2µF

±20%

6.3V

Ceramic, X5R

0603

1µF

4.7µF

±20%

6.3V

Ceramic, X5R

0603

1µF

±20%

6.3V

Ceramic, X5R

0603

1µF

±20%

6.3V

Ceramic, X5R

0603

2.2µF

±20%

6.3V

Ceramic, X5R

0603

240k

±1%

Bias Resistor

0201

PIN VBAT

BATTERY

Connector

L_total=L

Cin

Cbat

GND

C11

C12

Pins VBAT1

and VBAT2

PIN VBAT

BATTERY

Connector

Cin

Cbat

GND

L_total=L1+10xL2

C11

C12

Pins VBAT1

and VBAT2

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