Datasheet

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r rr rrrr rrrr0r0r0r0 r0r0
RAILVn
V = V
RAILn
R+
RAILVn
1024
x
PULLDOWN PULLUP
V = V
RAILn
R+
PULLDOWN
RAILVn R + R
1024 R
x x
UCD9081
www.ti.com SLVS813B –JUNE 2008–REVISED DECEMBER 2010
RAIL
For each of eight voltage rails, the UCD9081 has two registers that contain the rolling average voltage for the
associated rail as measured by the device. This average voltage is maintained in real-time by the UCD9081 and
is calculated as the output of a 4-TAP FIR filter. There are two registers for each voltage rail. One holds the
least-significant 8 bits of the voltage and the other the most-significant 2 bits of the voltage. This is shown in the
following table.
REGISTER NAME ADDRESS REGISTER CONTENTS
RAIL1H 0x00 RAIL1 voltage, bits 9:8
RAIL1L 0x01 RAIL1 voltage, bits 7:0
RAIL2H 0x02 RAIL2 voltage, bits 9:8
RAIL2L 0x03 RAIL2 voltage, bits 7:0
RAIL3H 0x04 RAIL3 voltage, bits 9:8
RAIL3L 0x05 RAIL3 voltage, bits 7:0
RAIL4H 0x06 RAIL4 voltage, bits 9:8
RAIL4L 0x07 RAIL4 voltage, bits 7:0
RAIL5H 0x08 RAIL5 voltage, bits 9:8
RAIL5L 0x09 RAIL5 voltage, bits 7:0
RAIL6H 0x0A RAIL6 voltage, bits 9:8
RAIL6L 0x0B RAIL6 voltage, bits 7:0
RAIL7H 0x0C RAIL7 voltage, bits 9:8
RAIL7L 0x0D RAIL7 voltage, bits 7:0
RAIL8H 0x0E RAIL8 voltage, bits 9:8
RAIL8L 0x0F RAIL8 voltage, bits 7:0
A rail voltage is read with a 16b access. The auto-increment feature of the UCD9081 allows multiple rail voltages
to be read with a single access.
A rail voltage is provided as a 10-bit binary value in an unsigned format, as shown following.
The following formulas can be used to calculate the actual measured rail voltage:
Without external voltage divider:
(1)
With external voltage divider:
(2)
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