DS1238S-10 Maxim Integrated Products, DS1238S-10 Datasheet - Page 4

• Manufacturer Part Number: DS1238S-10
• Description: IC MICROMAN W/FRESH 10% 16-SOIC
• Manufacturer: Maxim Integrated Products
• Series: MicroManagerr
• Type: Battery Backup Circuitr

Specifications of DS1238S-10

• Number Of Voltages Monitored: 1
• Output: Open Drain, Push-Pull
• Reset: Active High/Active Low
• Reset Timeout: 40 ms Minimum
• Voltage - Threshold: 4.37V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Table 1. The
pin with a falling edge, which will both set the
to leave the
falls below V
address, data, or control signals, as well as microcontroller port pins. Under normal operating conditions,
these signals would routinely reset the watchdog timer prior to time out. The watchdog is disabled by
leaving the
NON-MASKABLE INTERRUPT
The DS1238 generates a non-maskable interrupt (
microprocessor. A precision comparator monitors the voltage level at the IN pin relative to an on-chip
reference generated by an internal band gap. The IN pin is a high impedance input allowing for a user-
defined sense point. An external resistor voltage divider network (Figure 5) is used to interface with high
voltage signals. This sense point may be derived from the regulated 5-volt supply, or from a higher DC
voltage level closer to the main system power input. Since the IN trip point V
values for R1 and R2 can be determined by the equation as shown in Figure 5. Proper operation of the
DS1238 requires that the voltage at the IN pin be limited to V
voltage at the supply being monitored (V
approach to solving this equation is to select a value for R2 of high enough value to keep power
consumption low and solve for R1. The flexibility of the IN input pin allows for detection of power loss
at the earliest point in a power supply system, maximizing the amount of time for microprocessor
shutdown between
When the supply being monitored decays to the voltage sense point, the DS1238 will force the
output to an active state. Noise is removed from the
time domain hysteresis. That is, the monitored supply is sampled periodically at a rate determined by an
internal ring oscillator running at approximately 30kHz (33 s/cycle). Three consecutive samplings of
out-of-tolerance supply (below V
must be below the voltage sense point for approximately 100 s or the comparator will reset. In this way,
power supply noise is removed from the monitoring function preventing false trips. During a power-up,
any IN pin levels below V
V
Removal of an active low level on the
V
relationship between V
active. The
NMI
NMI
ST
CC
TP
. The initiation and removal of the
rises to V
INPUT TIMING Figure 2
to be virtually nonexistent on power up. This is of no consequence, however, since an RST will be
pin will enter a tri-state mode.
ST
NMI
ST
WDS
CCTP
CCTP
input open, or as soon as V
pin open, which disables the watchdog. Lastly, the
voltage will follow V
. As a result, any potential active
and activates the
NMI
pin will remain low until one of three operations occurs. The first is to strobe the
CC
and RST or
and the IN pin voltage. Note that a fast-slewing power supply may cause the
TP
detected by the comparator are disabled from reaching the
SENSE
RST
RVT
CC
) must occur at the IN pin to active
NMI
.
down until V
CC
NMI
MAX
signal. The
falls to V
pin is controlled by the subsequent rise of the IN pin above
) can also be derived as shown in Figure 5. A simple
signal during power up depends on the relative voltage
WDS
4 of 14
NMI
NMI
as well as the watchdog timer count. The second is
CCTP
CC
NMI
will not be initiated until V
ST
) for early warning of a power failure to the
decays to V
.
power-fail detection circuitry using built-in
input can be derived from microprocessor
IH
. Therefore, the maximum allowable
WDS
BAT
. Once V
pin is active low whenever V
NMI
TP
is 1.27 volts, the proper
CC
. Therefore, the supply
CC
decays to V
reaches V
NMI
I pin until
BAT
CCTP
DS1238
.
NMI
, the
ST
CC