LMK04832PAPSLASHEM datasheet(91/102 Pages) TI

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9.3 Power Supply Recommendations

9.3.1 Current Consumption

Current consumption varies considerably with the number of outputs and output formats. This can be calculated

the TI TICSPro software.

9.3.2 Cold Sparing Considerations

Figure 9-8 below demonstrates how this part can be used for cold sparing

220

Powered

LMK Device

Unpowered LMK

Device

(acting as cold spare)

CLKinX

–

VCC1 = 3.3V ± 0.3V

–

VCC2 = 0V

Output of LMK

Device configured

as CMOS

CLKINX or SYNC

Figure 9-8. Cold Sparing Devices Setup

9.3.2.1 Damage Prevention Details to Unpowered Device

Setting two devices in a cold sparing setup leads to the unpowered device receiving DC-coupled LVCMOS

pulses on the CLKIN0 or SYNC inputs periodically throughout the lifetime of the unpowered device. The

cumulative lifetime limit for the unpowered device DC input current is 10 hours at maximum junction

temperature. Also, the device can remain within specifications for much longer than this limit if the typical

cold-spare junction temperature is lower than maximum junction temperature. However, by placing a 220-Ω in

series between the output of the poweredde to the inputs of the unpowered devP, even when connected to a

3.3-V or 3.6-V powered system, DC pulses from the powered device do not damage the unpowered device.

DC-coupling 3.3V or 3.6-V I/O can occur without the transmitter for the SYNC signal failing high and destroying

the receiver, or any other circuitry within the unpowered device. Also, the 220-Ω resistor limits the current to

about 7 mA, with less than 12 mW dissipated onto the unpowered device.

Additionally, if CLKIN is damaged or fails short in one of the CLKIN paths with the 220-Ω resistor in series to

ground on the fault path, the current is limited. The initial damage won't short to the outputs of the transmitter

powered device, and therefore, no damage occurs to the rest of the system. The inputs and outputs of each

device have separate power supply pins that are not connected internally; therefore, if the unpowered device

is powered, no issues can occur to the outputs, even if one of the inputs is damaged over the lifetime of the

unpowered device.

When driving the CLKINx or OSCin inputs of an unpowered device, signal levels up to ± 400 mV can be

AC-coupled through 0.01 µF across the operating frequency range. Under these constraints, the magnitude of

the RMS currents injected into the CLKinX ESD structures is within acceptable power and current limits across

the full junction temperature range and won't cause long-term degradation of function. Larger amplitudes, higher

frequencies, or different coupling capacitors can be acceptable as long as the signal is AC-coupled and the

unpowered current limit of 7 mA going into or coming out of the CLKIN or OSCIN pins is observed.

www.ti.com

LMK04832-SEP

SNAS838A – OCTOBER 2022 – REVISED NOVEMBER 2022

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