LTC2928
9
2928fa
For more information www.linear.com/LTC2928
pin FuncTions
CAS: Cascade Input/Output. Connect the cascade pin be-
tween a master and one or more slave devices to increase
the number of supplies that can be sequenced per time
position.
See Applications Information for details. Do not
add capacitance to the cascade pin. Leave open if unused.
CMP1-CMP4: Comparator and/or Fault Status Outputs.
The CMP outputs have a weak internal pull-up to V
CC
and
may be pulled above V
CC
using an external pull-up. During
sequence-up or sequence-down operation, all compara-
tor outputs are low. After sequencing-up, during supply
monitoring
, comparator outputs pull low if their monitor
input drops below its under
voltage threshold. In the event
of a system fault, the CMP outputs latch and may be read
to diagnose the type and source of fault. See Applications
Information for the fault reporting details. Leave the CMP
outputs open if unused.
DONE: Sequence Done Output. The last (or only)
LTC2928 must have DONE pulled high with an external
resistor to V
CC
(3.3k 5% recommended). The LTC2928
floats DONE until the completion of a sequence-up
operation when it is pulled down. At the end of a
sequence-down operation, the LTC2928 returns DONE
to a high-impedance state. If subsequent time positions
are required for additional supplies, use the DONE—ON
handshake connection. See Applications Information
regarding the DONE—ON protocol.
EN1-EN4: Enable Outputs. Connect these outputs to a power
supply shutdown input or an external N-channel MOSFET
gate for the supply to be sequenced. When enabled, each
output is connected to an internal charge pumped sup
-
ply (nominally V
CC
+ 5.5V) via an internal 10µA current
source. When disabled, each output is pulled to ground.
EN outputs operate with their respective RT inputs. Leave
enable outputs open when unused.
Exposed Pad: Exposed pad may be left floating or con
-
nected to device ground.
F
LT :
Fault Input/Output. Pull F LT high with an external
resistor (10k recommended). The LTC2928 will pull F LT
low if an internal fault condition is detected (see Applica
-
tions Information for details). An external signal such as
OV may also pull down the
F LT pin to cause an external
fault. Any internal or external fault condition forces all
enable outputs low. In order to clear a fault condition, a
“return-to-zero” state must be reached with all monitored
supplies falling below their configured sequence-down
thresholds, while the ON input is below 0.97V. Debugging
modes are available (use the MS1, MS2 inputs) to leave
supplies enabled upon system faults. See Applications
Information for configuration tables.
GND: Device ground.
HV
CC
: High Voltage (7.2V to 16.5V) Power Supply Input.
Bypass HV
CC
with at least 0.1µF to ground in close prox-
imity to this pin. The internal HV
CC
regulator provides a
regulated 3.3V to V
CC
. V
CC
may be used to power exter-
nal circuits (limited to 10 mA external load). Tie HV
CC
to
ground when unused.
MS1, MS2: Master/Slave Three State Configuration In
-
puts. Depending on the application, select each LTC2928
as a master or slave part and whether or not the part is
designated as the first part in a cascade application. The
RST—F LT relationship (after RST pulls high for the first
time) is also configured with these inputs. Select whether
or not RST pulling low should cause F LT to pull low and
shutdown the system. Select debugging modes to leave
supplies enabled upon system faults. See Applications
Information for configuration table.
N/C: No Connect. Unconnected pins.
ON: Sequence Up/Down Input. A voltage transition above
1V starts the sequence-up phase. A voltage transition below
0.97V starts the sequence-down phase. An ON transition
applied during a sequence-up (or down) phase is treated
as a command fault. See Applications Information for us
-
ing the DONE—ON handshake protocol when cascading
multiple LTC2928s to append additional time positions.
