AM3892 datasheet(135/299 Pages) TI

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CLKIN32

AM3894

AM3892

www.ti.com

SPRS681A – OCTOBER 2010 – REVISED MARCH 2011

Table 7-8. Exceptions to REFCLK AC Specification for LVDS Clock Sources

SYMBOL

PARAMETER

MIN

MAX

UNIT

VIH

Differential input high voltage (VIH)

125

1000

VIL

Differential input high voltage (VIL)

-1000

-125

Table 7-9. SERDES_CLKN/P Routing Specifications

PARAMETER

MIN

TYP

MAX

UNIT

Number of stubs allowed on SERDES_CLKN/P traces

Stubs

SERDES_CLKN/P trace length from oscillator to device

2000

Mils

SERDES_CLKN/P pair differential impedance

100

Ohms

Number of vias on each SERDES_CLKN/P trace(1)

Vias

SERDES_CLKN/P differential pair to any other trace spacing

2*DS(2)

(1)

Vias must be used in pairs with their distance minimized.

(2)

DS is the differential spacing of the SERDES_CLKN/P traces.

AC coupling capacitors are required on the SERDES_CLKN/P pair. Table 7-10 shows the requirements

for these capacitors.

Table 7-10. SERDES_CLKN/P AC Coupling Capacitors Requirements

PARAMETER

MIN

TYP

MAX

UNIT

SERDES_CLKN/P AC coupling capacitor value

SERDES_CLKN/P AC coupling capacitor package size

0402

Mils(1)(2)

(1)

LxW, 10 mil units, i.e., a 0402 is a 40x20 mil surface mount capacitor.

(2)

The physical size of the capacitor should be as small as possible

7.3.3

CLKIN32 Input Clock

An external 32.768-kHz clock input can optionally be provided at the CLKIN32 pin to serve as a reference

clock in place of the RTCDIVIDER clock for the RTC and Timer modules. The CLKIN32 source must meet

the timing requirements shown in Table 7-11.

Table 7-11. Timing Requirements for CLKIN32(1)(2)

(see Figure 7-7)

NO.

MIN

NOM

MAX

UNIT

tc(CLKIN32)

Cycle time, CLKIN32

1/32768

tw(CLKIN32H)

Pulse duration, CLKIN32 high

0.45C

0.55C

tw(CKIN32L)

Pulse duration, CLKIN32 low

0.45C

0.55C

tt(CLKIN32)

Transition time, CLKIN32

tJ(CLKIN32)

Period jitter, CLKIN32

0.02C

(1)

The reference points for the rise and fall transitions are measured at V IL MAX and V IH MIN.

(2)

C = CLKIN32 cycle time, in ns. For example, when CLKIN32 frequency is 32768 Hz, use C = 1/32768 s.

Figure 7-7. CLKIN32 Timing

Power, Reset, Clocking, and Interrupts

135

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