LMK01000
www.ti.com
SNAS437G –FEBRUARY 2008–REVISED OCTOBER 2009
CURRENT CONSUMPTION / POWER DISSIPATION CALCULATIONS (Vcc = 3.3 V, TA= 25° C)
Current Power
Power
Consumption Dissipated in
Block Condition Dissipated in
at 3.3 V LVPECL emitter
device (mW)
(mA) resistors (mW)
Core Current All outputs disabled. Includes input buffer currents. 19 62.7 -
Low clock buffer The low clock buffer is enabled anytime one of CLKout0 through 9 29.7 -
(internal) CLKout3 are enabled
High clock The high clock buffer is enabled anytime one of the CLKout4 9 29.7 -
buffer (internal) through CLKout7 are enabled
LVDS output, Bypassed mode 17.8 58.7 -
LVPECL output, Bypassed mode 40 72 60
(includes 120 Ωemitter resistors)
Output buffers LVPECL output, disabled mode 17.4 38.3 19.1
(includes 120 Ωemitter resistors)
LVPECL output, disabled mode. 0 0 -
No emitter resistors placed; open outputs
Additional current per channel due LVPECL Output 0.5 1.65 -
Vboost to setting Vboost from 0 to 1. LVDS Output 1.5 5.0
Divide enabled, divide = 2 5.3 17.5 -
Divide circuitry
per output Divide enabled, divide > 2 8.5 28.0 -
Delay enabled, delay < 8 5.8 19.1 -
Delay circuitry
per output Delay enabled, delay > 7 9.9 32.7 -
Entire device LMK01000 85.8 223.1 60
CLKout0 & LMK01010 63.6 209.9 -
CLKout4
enabled in LMK01020 108 236.4 120
Bypassed mode
Entire device LMK01000 323.8 768.5 300
all outputs LMK01010 212.8 702.3 -
enabled with no
delay and divide LMK01020 390.4 808.3 480
value of 2
From the above table, the current can be calculated in any configuration. For example, the current for the entire
device with 1 LVDS (CLKout0) & 1 LVPECL (CLKout4) output in Bypassed mode can be calculated by adding up
the following blocks: core current, low clock buffer, high clock buffer, one LVDS output buffer current, and one
LVPECL output buffer current. There will also be one LVPECL output drawing emitter current, but some of the
power from the current draw is dissipated in the external 120 Ωresistors which doesn't add to the power
dissipation budget for the device. If delays or divides are switched in, then the additional current for these stages
needs to be added as well.
For power dissipated by the device, the total current entering the device is multiplied by the voltage at the device
minus the power dissipated in any emitter resistors connected to any of the LVPECL outputs. If no emitter
resistors are connected to the LVPECL outputs, this power will be 0 watts. For example, in the case of 1 LVDS
(CLKout0) & 1 LVPECL (CLKout4) operating at 3.3 volts for LMK01000, we calculate 3.3 V × (10 + 9 + 9 + 17.8
+ 40) mA = 3.3 V × 85.8 mA = 283.1 mW. Because the LVPECL output (CLKout4) has the emitter resistors
hooked up and the power dissipated by these resistors is 60 mW, the total power dissipation is 283.1 mW - 60
mW = 223.1 mW. When the LVPECL output is active, ~1.9 V is the average voltage on each output as calculated
from the LVPECL Voh & Vol typical specification. Therefore the power dissipated in each emitter resistor is
approximately (1.9 V)2/ 120 Ω= 30 mW. When the LVPECL output is disabled, the emitter resistor voltage is
~1.07 V. Therefore the power dissipated in each emitter resistor is approximately (1.07 V)2/ 120 Ω= 9.5 mW.
THERMAL MANAGEMENT
Power consumption of the LMK01000 family device can be high enough to require attention to thermal
management. For reliability and performance reasons the die temperature should be limited to a maximum of
125 °C. That is, as an estimate, TA(ambient temperature) plus device power consumption times θJA should not
exceed 125 °C.
Copyright © 2008–2009, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LMK01000