LTC3882-1
53
Rev A
38821 F34
100ms/DIV
VOUT2
VOUT3
VOUT4
VOUT1
1V/DIV
APPLICATIONS INFORMATION
Figure 34. LTC3882-1 Time-Based Ratiometric Ramping
Figure 35. Cascade Sequencing Configuration
LTC3882-1
PGOOD0
PGOOD1
RUN 1
RUN 0
START
LTC3882-1
38821 F35
RUN 0
PGOOD0
PGOOD1
TO NEXT CHANNEL
IN THE SEQUENCE
(PGOOD PULL-UP RESISTORS
TO 3.3V NOT SHOWN)
RUN 1
Figure 31. Example of 1ms TON_RISE
Figure 33. LTC3882-1 Time-Based Coincident Supply Ramping
Figure 32. LTC3882-1 Time-Based Supply Sequencing
Figure 35. This configuration hardware disables the next
downstream controller anytime the output is not within
the specified UV and OV limits, or the upstream controller
is disabled. When indicating power is not good, there is
a 30µs deglitching filter on the PGOOD output to assure
the signal does not toggle repeatedly at lower values of
TON_RISE/FALL due to noise on V
OUT
. If unwanted transi-
tions still occur on PGOOD due to noise or longer rise/fall
settings, place a capacitor to ground on the PGOOD pin
to further filter the waveform. The RC time-constant of
the filter should be low enough to assure no appreciable
delay is incurred. A value of 300μs to 500μs will provide
some additional filtering without significantly delaying
the trigger event.
38821 F31
V
OUT
(1V/DIV)
RUN
(5V/DIV)
200µs/DIV
38821 F32
VOUT2
VOUT3
VOUT4
VOUT1
100ms/DIV
1V/DIV
38821 F33
100ms/DIV
VOUT2
VOUT3
VOUT4
VOUT1
1V/DIV
38821 F36
100ms/DIV
VOUT2
VOUT3
VOUT4
VOUT1
1V/DIV
Figure 36. Cascade Sequencing Waveforms
When the system is turned off, rails will shut down in the
same order as they turn on, as shown in Figure 36. If a
different sequence is required, the circuit must be rewired
or delays must be added by programming TON_DELAY or
TOFF_DELAY. A fundamental limitation of this application is
the inability of upstream rails to detect a start-up failure of
