Datasheet

LTC2928
21
2928f
Forcing Supplies Off or Disabling Unused Channels
The most convenient way to mask an unused channel is
to tie its respective RT input to ground. After sequenc-
ing begins, any enable output (EN) may be pulled low
permanently by driving the respective RT input to ground
(asynchronous OFF command). An asynchronously OFF
channel cannot be re-enabled until a new sequence-up
procedure is started. Any channel that is asynchronously
OFF is removed from participation in the sequencing and
supply monitoring processes, allowing the LTC2928 to
operate normally on the remaining operating channels.
When experiencing a fault in the “No Shutdown Debug
Mode”, the asynchronous OFF feature may be used to
conveniently pull down the enable outputs. Alternatively,
V
CC
may be turned off and on again. Clearing a fault con-
dition requires the ON input to be low while the supplies
are below their sequence-down thresholds.
Forcing Supplies On Prior to Sequencing
Prior to sequencing, any or all enable pins may be forced
high by pulling the respective RT pin to V
CC
. In this man-
ner, supplies may be tested individually or together in any
combination. With any RT pin at V
CC
, the respective voltage
monitor inputs and comparator outputs become active with
thresholds parked at the configured sequence-up thresh-
old. Outside of sequencing, RST (with 100% thresholds
selected) and OV are always functional, regardless of
RT pin state. If all four RT pins are at V
CC
, the LTC2928
can be used as a stand-alone quad voltage monitor with
under- and overvoltage indication as shown in Figure 11
(100% thresholds). With ON low in the RT forcing mode,
sequence, command and reset faults do not occur. External
faults however, may be detected (overvoltage, for example).
Any previously logged faults remain in memory and their
reporting will return upon exiting the forcing mode.
EN1
LTC2928
EN2
EN3
EN4
RT1HV
CC
3.32k
SUPPLY
BANK
0.047
F
V
CC
0.1 F
RT4
CMP1
CMP2
CMP3
CMP4
SQT2
SQT1
ON
V1
V2
V3
V4
MS1
MS2
RT2
RT3
VSEL
GND
RTMR
PTMR
STMR
V
CC
REF
OVA
DONE
FLT
OV
RDIS
CAS
RST
10k
10k
10k
10k
10k
52.3k
3.3V
1.8V
1.5V
2.5V
23.7k
17.8k
36.5k
10k
2928 TA05
SYSTEM
LOGIC
Figure 11. Quad Supervisor (No Sequencing)
APPLICATIO S I FOR ATIO
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