Datasheet

V33A
V33D
V33DIO1
V33DIO2
UCD90124A
AVSS1
AVSS2
AVSS3
DVSS1
DVSS2
DVSS3
C
3.3V
B340A
UCD90124A
www.ti.com SLVSAN8 –JANUARY 2012
Figure 31. Brownout Circuit
PMBUS ADDRESS SELECTION
Two pins are allocated to decode the PMBus address. At power up, the device applies a bias current to each
address-detect pin, and the voltage on that pin is captured by the internal 12-bit ADC. The PMBus address is
calculated as follows.
PMBus Address = 12 × bin(V
AD01
) + bin(V
AD00
)
Where bin(V
AD0x
) is the address bin for one of eight addresses as shown in Table 9. The address bins are
defined by the MIN and MAX VOLTAGE RANGE (V). Each bin is a constant ratio of 1.25 from the previous bin.
This method maintains the width of each bin relative to the tolerance of standard 1% resistors.
Table 9. PMBus Address Bins
RPMBus
ADDRESS BIN
PMBus RESISTANCE (kΩ)
open —
11 200
10 154
9 118
8 90.9
7 69.8
6 53.6
5 41.2
4 31.6
short —
A low impedance (short) on either address pin that produces a voltage below the minimum voltage causes the
PMBus address to default to address 126 (0x7E). A high impedance (open) on either address pin that produces
a voltage above the maximum voltage also causes the PMBus address to default to address 126 (0x7E).
Address 0 is not used because it is the PMBus general-call address. Addresses 11 and 127 can not be used by
this device or any other device that shares the PMBus with it, because those are reserved for manufacturing
programming and test. It is recommended that address 126 not be used for any devices on the PMBus, because
this is the address that the UCD90124A defaults to if the address lines are shorted to ground or left open.
Table 10 summarizes which PMBus addresses can be used. Other SMBus/PMBus addresses have been
assigned for specific devices. For a system with other types of devices connected to the same PMBus, see the
SMBus device address assignments table in Appendix C of the latest version of the System Management Bus
(SMBus) specification. The SMBus specification can be downloaded at http://smbus.org/specs/smbus20.pdf.
Table 10. PMBus Address Assignment Rules
Address STATUS Reason
0 Prohibited SMBus generaladdress call
1-10 Available
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