Datasheet

LTC2974
17
2974fc
For more information www.linear.com/LTC2974
operaTion
Figure 1: AUXFAULTB MUX
AUXFAULTB
2974 F01
FAST
PULL-DOWN
OV/UV/OC/UC
(MASKABLE)
OFF_THEN_ON
OR
FAULT_RETRY
FOR ANY CHANNEL
PMBUS
COMMAND
fault_seen
WEAK 12V PULL-UP
HI-Z
RESET
SET
Q
EEPROM
The LTC2974 contains internal EEPROM (Non-Volatile
Memory) to store configuration settings and fault log
information. EEPROM endurance, retention and mass
write operation time are specified over the operating tem
-
perature range. See Electrical Characteristics and Absolute
Maximum Ratings sections.
Non destructive operation above T
J
= 85°C is possible
although the Electrical Characteristics are not guaranteed
and the EEPROM will be degraded.
Operating the EEPROM above 85°C may result in a deg
-
radation of retention characteristics. The fault logging
function, which is useful in debugging system problems
that may occur at high temperatures, only writes to fault
log EEPROM locations. If occasional writes to these reg
-
isters occur above 85°C, a slight degradation in the data
retention characteristics of the fault log may occur
.
It is recommended that the EEPROM not be written using
STORE_USER_ALL or bulk
programming when T
J
> 85°C.
The degradation in EEPROM retention for temperatures
>85°C can be approximated by calculating the dimension
-
less acceleration factor using the following equation.
AF = e
Ea
k






•
1
T
USE
+273
–
1
T
STRESS
+273












Where:
AF = acceleration factor
Ea = activation energy = 1.4eV
k = 8.625 • 10
–5
eV/°K
T
USE
= 85°C specified junction temperature
T
STRESS
= actual junction temperature °C
Example: Calculate the effect on retention when operating
at a junction temperature of 95°C for 10 hours.
T
STRESS
= 95°C
T
USE
= 85°C
AF = 3.4
Equivalent operating time at 85°C = 34 hours.
So the overall rentention of the EEPROM was degraded by
34 hours as a result of operation at a junction temperature
of 95°C for 10 hours. Note that the effect of this overstress
is negligible when compared to the overall EEPROM
rentention rating of 87,600 hours at a maximum junction
temperature of 85°C.
AUXFAULTB
The AUXFAULTB pin can be commanded to one of two
output levels at any time via the PMBUS. If desired, the
AUXFAULTB pin can also be configured to indicate when
some fault conditions have been detected, using a third
output level. See Figure 1 for a conceptual view of this
multiplexing.
The MFR_CONFIG2_LTC2974 and MFR_CONFIG3_
LTC2974 commands can be used on a per channel basis
to select which, if any, fault conditions will cause the
AUXFAULTB pin to be driven to its third output level (fast
pull-down to GND). The only fault types which can be
propagated to the AUXFAULTB pin are over/under voltage
faults and over/under current faults.
Mfr_config_all_auxfaultb_wpu selects whether the
AUXFAULTB pin is in the hi-Z state, or weakly pulled-up
to approximately 12V, using a 5µA current. As shown in
Figure 1, the pulldown to GND overrides if any enabled
faults are detected.