What Does 5% Power Supply
Tolerance Mean ?
TI Confidential – NDA Restrictions
Tolerance Considerations
• When a specific power supply tolerance is
specified for a device this includes all sources of
error and the power distribution network (PDN)
should be designed to ensure that the required
tolerance is met at the device power balls
TI Confidential – NDA Restrictions
Tolerance Requirements Definition
• The power supply tolerance is specified with
respect to the target voltage and not the overall
device max/min specification.
•V
•VTarget +5%
•VTarget
•VTarget –5%
•Out of spec
p
•Within spec
•Out of spec
•t
• For Smart Reflex supplied devices this means
that the tolerance is with respect to the SR target
voltage.
g The only
y time deviation is allowed is
during a SR voltage transition step
TI Confidential – NDA Restrictions
Sources of Error
• Board trace resistance will cause an IR drop
proportional to the nominal current. Low frequency
changes in current will cause low frequency
changes in the voltage at the device
• Board trace impedance and capacitor
selection/placement/connectivity will cause a voltage
change
g due to high
g frequency
q
y changes
g in current.
Incorrect capacitor selection can also cause
resonance which in turn causes voltage changes
• PMIC switching will cause switching ripple
• The sum of ALL these sources of error must be
accounted for and meet the 5% tolerance
requirement
TI Confidential – NDA Restrictions
Examples
•V
•V1 + 5%
•V
V1=1.05V
=1 05V
•
•V1 – 5%
Good
G
d behavior.
b h i
Only time deviation
from 5% is during
step changes
•V2 +5%
•V2=900mV
•V2 –5%
•Calibration
d
and
Convergence
•Power-up &
Boot-up
•AVS
Driver
Enabled
•V
•VNominal +α%
•VNominal
•VNominal –α%
•Application
running
•AVS Driver
Calibration
routine
completes
p
•t
•Application running
•
•Out of spec
•∆t = 1us
•t
TI Confidential – NDA Restrictions
Bad behavior.
Deviation exists
due to short term
increase in current
requirements
SR cannot
compensate
Smart Reflex
• Class 2 Smart Reflex ((AVS)) adjusts
j
the nominal voltage
g
based on average device performance measurement,
not an absolute or instantaneous voltage measurement.
• Once the nominal voltage is determined the system PDN
must maintain tolerance around this nominal voltage.
• The performance assessment and nominal voltage
update is a very low frequency operation and cannot
account for voltage change due to load transients, board
resonances or regulator ripple.
• SR iis d
designed
i
d tto accountt ffor ageing
i and
dd
device
i
temperature changes and any PMIC voltage accuracy
(E.g. ask for to 0.950 but get 0.925).
TI Confidential – NDA Restrictions