LTC2935IDC-1#PBF Linear Technology, LTC2935IDC-1#PBF Datasheet - Page 7

• Manufacturer Part Number: LTC2935IDC-1#PBF
• Manufacturer: Linear Technology

Specifications of LTC2935IDC-1#PBF

• Voltage Supervisor Type: Voltage Monitor
• Number Of Voltage Supervisors: 1
• Operating Supply Voltage (max): 5.5V
• Operating Temperature Classification: Industrial
• Operating Temp Range: -40C to 85C
• Pin Count: 8
• Mounting: Surface Mount
• Lead Free Status / Rohs Status: Compliant

APPLICATIONS INFORMATION
VOLTAGE MONITORING
Unmanaged power can cause various system problems.
At power-up, voltage fl uctuation around critical thresholds
can cause improper system or processor initialization.
The LTC2935 provides power management capabilities
for the system power-up phase. The supervisory device
issues a system reset after the monitored voltage has
stabilized. Built-in hysteresis and fi ltering ensures that
fl uctuations due to load transients or supply noise do
not cause chattering of the status outputs. Comparator
undervoltage glitch immunity is shown in the Typical
Performance Characteristics section. The curve dem-
onstrates the transient amplitude and width required to
switch the comparators.
Because many batteries exhibit large series resistance,
load currents can cause signifi cant voltage drops. The
low DC current draw of the LTC2935 (at any input volt-
age) does not add to the loading problem. When voltage
is initially applied to V
is enough voltage to turn on the pull-down devices (1V
maximum).
If the monitored supply voltage falls to the power-fail
threshold, the built-in power-fail comparator pulls PFO
low. At this point, there remains 150mV of voltage mar-
gin before the RST output pulls low. PFO remains low
until V
hysteresis. PFO is typically used to signal preparation for
controlled shutdown. For example, the PFO output may
be connected to a processor nonmaskable interrupt. Upon
interrupt, the processor may begin shutdown procedures.
Shutdown events may include supply sequencing and/or
storage/erasure of system state in nonvolatile memory.
If the monitored voltage drops below the reset threshold,
RST pulls low until V
CC
rises above the power-fail threshold plus 2.5%
CC
CC
rises above the reset threshold plus
, RST and PFO pull low once there
5% hysteresis. This may occur through battery charging
or replacement. An internal reset timer delays the return
of the RST output to a high state to provide settling and
initialization time. The RST output is typically connected
to a processor reset input.
Few, if any external components are necessary for reliable
operation. However, a decoupling capacitor between V
and ground is recommended (0.01μF minimum).
Threshold Confi guration
The LTC2935 monitors and compares the V
against two internal thresholds during operation. The
higher threshold (power-fail) is the level used for early
warning of a low voltage condition, reported on the PFO
output. The lower threshold (reset) is the level at which
the RST output pulls low. Use system requirements to
choose the appropriate reset threshold from Table 1. The
power-fail threshold is always 150mV higher than the
confi gured reset threshold. Set the threshold selection
inputs (S2, S1, S0) accordingly.
Table 1. Falling Threshold Selection
THRESHOLD
RESET
3.30
3.15
3.00
2.85
2.70
2.55
2.40
2.25
(V)
POWER-FAIL
THRESHOLD
3.45
3.30
3.15
3.00
2.85
2.70
2.55
2.40
(V)
High
High
High
High
Low
Low
Low
Low
S2
High
High
High
High
Low
Low
Low
Low
LTC2935
S1
CC
voltage
High
High
High
High
Low
Low
Low
Low
S0
7
2935f
CC