AM3703CUS datasheet(134/280 Pages) TI

134 / 280 page

Device

sys_xtalin

sys_xtalgnd

sys_xtalout

Cf1

Cf2

Crystal

AM3715, AM3703

SPRS616F

– JUNE 2010 – REVISED AUGUST 2011

www.ti.com

4.1.2

sys_xtalin / sys_xtalout External Crystal

An external crystal is connected to the device pins. Figure 4-2 describes the crystal implementation.

Figure 4-2. Crystal Implementation

1. When the crystal oscillator is in bypass mode (crystal implementation is unused), the sys_xtalgnd ball

is not connected.

The crystal must be in the fundamental mode of operation and parallel resonant. Table 4-2 summarizes

the required electrical constraints.

Table 4-2. Crystal Electrical Characteristics(1)

NAME

DESCRIPTION

MIN

TYP

MAX

UNIT

Parallel resonance crystal frequency(1)

12, 13, 16.8, or 19.2

MHz

Cf1

Cf1 load capacitance for crystal parallel resonance with Cf1 = Cf2

Cf2

Cf2 load capacitance for crystal parallel resonance with Cf1 = Cf2

ESR(Cf1,Cf2)

(2)

Frequency 12 MHz , Negative resistor at nominal 500

Ω, Negative

100

Ω

resistor at worst case 300

Ω

Frequency 13 MHz, Negative resistor at nominal 400

Ω, Negative

Ω

resistor at worst case 240

Ω

Frequency 16.8 MHz and 19.2 MHz, Negative resistor at nominal

Ω

300

Ω, Negative resistor at worst case 180 Ω

Crystal shunt capacitance

4.5

Crystal drive level

0.5

(1) Measured with the load capacitance specified by the crystal manufacturer. This load is defined by the foot capacitances tied in series. If

CL = 20 pF, then both foot capacitors will be Cf1 = Cf2 = 40 pF. Parasitic capacitance from package and board must also be taken in

account.

(2) The crystal motional resistance Rm is related to the equivalent series resistance (ESR) by the following formula:

ESR = Rm * (1 + (CO * Cf1 * Cf2 / (Cf1 + Cf2)))

When selecting a crystal, the system design must take into account the temperature and aging

characteristics of a crystal versus the user environment and expected lifetime of the system.

134

Clock Specifications

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