Datasheet

ADP1046A Data Sheet
Rev. 0 | Page 26 of 88
Figure 35 shows the possible signals on the share bus.
LOGIC 1
LOGIC 0
IDLE
PREVIOUS
BIT
NEXT
BIT
t
1
t
0
t
BIT
11012-025
Figure 35. Share Bus High, Low, and Idle Bits
The length of a bit (t
BIT
) is fixed at 10 μs. A Logic 1 is defined as
a high-to-low transition at the start of the bit and a low-to-high
transition at 75% of t
BIT
. A Logic 0 is defined as a high-to-low
transition at the start of the bit and a low-to-high transition at
25% of t
BIT
.
The bus is idle when it is high during the whole period of t
BIT
.
All other activity on the bus is illegal. Glitches up to t
GLITCH
(200 ns) are ignored.
The digital word that represents the current information is eight
bits long. The ADP1046A takes the eight MSBs of the CS2 read-
ing and uses this reading as the digital word (see Figure 36).
Digital Share Bus Scheme
Each power supply compares the digital word that it is outputting
with the digital words of all the other supplies on the bus.
Round 1
In Round 1, every supply first places its MSB on the bus. If a
supply senses that its MSB is the same as the value on the bus, it
continues to Round 2. If a supply senses that its MSB is less than
the value on the bus, it means that this supply must be a slave.
When a supply becomes a slave, it stops communicating on the
share bus because it knows that it is not the master. The supply then
increases its output voltage in an attempt to share more current.
If two units have the same MSB, they both continue to Round 2
because either of them may be the master.
Round 2
In Round 2, all supplies that are still communicating on the bus
place their second MSB on the share bus. If a supply senses that
its MSB is less than the value on the bus, it means that this supply
must be a slave and it stops communicating on the share bus.
Round 3 to Round 8
The same algorithm is repeated for up to eight rounds to allow
supplies to compare their digital words and, in this way, to
determine whether each unit is the master or a slave.
Digital Share Bus Configuration
The digital share bus can be configured in various ways. The band-
width of the share bus loop is programmable in Register 0x29[2:0].
The extent to which a slave tries to match the current of the master
is programmable in Register 0x2A[3:0]. Enable the digital share
bus by setting Register 0x29[3] to 1.
CURRENT
SENSE
ADC
1 LSB = 29.3µV
35mV/29.3µV = 1195
MASTER
+
35mV
–
DIGITAL
WORD
DIGITAL
FILTER
÷16
12 BITS
1195 DEC
0x4AB
8 BITS
74 DEC
0x4A
0x4A
SHAREi
CS2+
CS2–
V
DD
SHARE
BUS
8-BIT
WORD
0xB5
8-BIT
WORD
0x4A
SHAREo
I
OUT
= 35A
1mΩ
PSU A
11012-026
Figure 36. How the Share Bus Generates the Digital Word to Place on the Digital Share Bus