LTC2928CUHF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2928CUHF' PDF : 34 Pages View PDF
LTC2928
Timing Diagrams
ON
CAS
STMR
Vx
RST
RTMR
CAS and STMR Relationship
tCAS(MINIMUM)
tSTMR
tSTMR
15 CYCLES
Undervoltage Timing
tMON(UV)
VMON(TH)
tRTMR
7 CYCLES
The LTC2928 monitors four supply thresholds per supply
(sequence-up, sequence-down, undervoltage, overvolt-
age) during a full system cycle. A full cycle comprises a
sequence-up phase, monitor phase and sequence-down
phase. A sequence timer sets the time delay between supply
enables during both the sequence-up and sequence-down
phases. The power-good timer is a watchdog for stalled
supplies during the sequence-up and sequence-down
phases. A microprocessor reset signal is issued once all
supplies are above their undervoltage threshold for the
chosen reset time. During the monitor phase, all enabled
supply voltages are continuously compared with their
undervoltage threshold. If any supply falls below its
undervoltage threshold, the reset output pulls low. The
reset output pulls high once all enabled supplies have
been in compliance for the chosen reset time. During any
phase, all positive supplies are continuously monitored
for overvoltage conditions.
Vx
OV
RTMR
Overvoltage Timing
tMON(OV)
VOV(TH)
tRTMR
Implementing complex power-on and power-off schemes
is simple using the LTC2928. System errors are easily
diagnosed with the LTC2928 fault event reporting feature.
Basic LTC2928 operation is discussed below. Configura-
tion tables are given in the Applications Information sec-
tion. The Applications Information also includes many
of the unique and advantageous extensions to the basic
operation, such as Master/Slave configurations.
7 CYCLES
2928F13 Sequence-Up Phase
Operation
The LTC2928 is a four channel, cascadable power supply
sequencer and supervisor for use with external N-channel
MOSFETs or power supplies with shutdown/enable inputs.
An unlimited number of power supplies may be fully
sequenced at configurable points in time using multiple
LTC2928s. A single LTC2928 controls up to four supplies
(four positives or three positives and one negative) and
one external resistor per supply configures each supply
enable (disable) time position. Device power is applied
through either VCC (2.9V to 6V) or HVCC (7.2V to 16.5V).
When applying power through HVCC, a regulated 3.3V is
output on VCC. An internal charge pump provides (VCC
+ 5.5V) gate drive voltages at the enable outputs EN1 to
EN4 for driving external pass FETs.
While VCC is ramping up, the LTC2928 enters a power-on
mode and pulls down its CAS pin. When VCC is stabilized,
the LTC2928 is configured for operation and releases its
CAS pin. Multiple LTC2928s with common CAS connections
will therefore synchronize with each other. The ON input is
used to start the sequence-up and sequence-down process.
The state of ON is ignored until CAS is released. When the
voltage at the ON input exceeds 1V, the sequence-up phase
is enabled after a small propagation delay (20µs typical).
If the ON signal prematurely pulls below 0.97V during the
sequence-up phase, a command fault is generated, caus-
ing enable (EN) outputs to pull low. For more details refer
to the discussion on system faults later in this document.
At the beginning of the sequence-up phase, a current
source begins to charge the STMR capacitance. When
2928fa
For more information www.linear.com/LTC2928
13
Share Link: 
