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DS1374C-3#

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18
I
BAT0SC1
vs. V
BAT
SQUARE-WAVE OFF
DS1374 toc01
V
BAT
(V)
SUPPLY CURRENT (nA)
5.34.84.33.83.32.82.31.8
350
400
450
500
550
300
1.3
V
CC
= 0V
DS1374
I
2
C, 32-Bit Binary Counter Watchdog RTC with
Trickle Charger and Reset Input/Output
_____________________________________________________________________
7
Typical Operating Characteristics
(V
CC
= +3.3V, T
A
= +25°C, unless otherwise noted.)
I
BAT0SC2
vs. V
BAT
SQUARE-WAVE ON
DS1374 toc02
400
450
500
550
600
650
700
750
800
350
V
CC
= 0V
V
BAT
(V)
SUPPLY CURRENT (nA)
5.34.84.33.83.32.82.31.81.3
I
BATOSC1
vs. TEMPERATURE
V
BAT
= 3.0V
DS1374 toc03
TEMPERATURE (°C)
SUPPLY CURRENT (nA)
806040200-20
400
425
450
475
375
-40
V
CC
= 0V
I
CCA
vs. V
CC
(SQUARE-WAVE ON)
DS1374 toc04
V
CC
(V)
SUPPLY CURRENT (μA)
5.34.83.8 4.32.8 3.32.3
75
100
125
150
175
200
225
250
275
50
1.8
OSCILLATOR FREQUENCY vs. V
BACKUP
DS1374 toc05
V
BACKUP
(V)
FREQUENCY (Hz)
5.34.84.33.83.32.82.31.8
32768.3
32768.4
32768.5
32768.6
32768.7
32768.8
32768.2
32768.1
32768.0
1.3
V
CC
= 0V
V
CC
FALLING vs. RST DELAY
DS1374 toc06
V
CC
FALLING (V/ms)
RESET DELAY (μs)
1010.10
1
10
100
1000
0.1
0.01 100
V
CC
= 3.0V TO 0V
DS1374
I
2
C, 32-Bit Binary Counter Watchdog RTC with
Trickle Charger and Reset Input/Output
8 _____________________________________________________________________
Pin Description
PIN
μSOP SO
NAME FUNCTION
1, 2 — X1, X2
Connections for a Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is designed
for operation with a crystal having a specified load capacitance (C
L
) of 6pF. Pin X1 is the input to the
oscillator and can optionally be connected to an external 32.768kHz oscillator. The output of the
internal oscillator, pin X2, is left unconnected if an external oscillator is connected to pin X1.
3 13 V
BACKUP
Connection for a Secondary Power Supply. This supply is used to operate the oscillator and
counters when V
CC
is absent. Supply voltage must be held between 1.3V and 3.7V (-18 and -3) or
1.3V and 5.5V (-33) for proper operation. This pin can be connected to a primary cell such as a
lithium cell. Additionally, this pin can be connected to a rechargeable cell or a super cap when
used with the trickle-charge feature. UL recognized to ensure against reverse charging when used
with a lithium battery. This pin must be grounded if not used.
4 14 RST
Active-Low, Open-Drain Output with a Debounced Pushbutton Input. This pin can be activated by a
pushbutton reset request, a watchdog alarm condition, or a power-fail event. It has an internal 50k
pullup resistor. No external resistors should be connected. If the crystal oscillator is disabled, the
startup time of the oscillator is added to the t
RST
delay.
5 15 GND Ground
6 16 SDA
Serial Data Input/Output. SDA is the input/output for the 2-wire serial interface. The SDA pin is open
drain and requires an external pullup resistor.
7 1 SCL
Serial Clock Input. SCL is the clock input for the 2-wire serial interface and is used to synchronize
data movement on the serial interface.
8 2 INT
Interupt. This pin is used to output the alarm interrupt or the watchdog reset signal. It is active-low
open drain and requires an external pullup resistor.
9 3 SQW
Square-Wave Output. This pin is used to output the programmable square-wave signal. It is open
drain and requires an external pullup resistor.
10 4 V
CC
DC Power for Primary Power Supply
— 5–12 N.C. No Connection. Must be connected to ground.
CLOCK
DIVIDER
32-BIT
COUNTER
MUX
4.096kHz
1Hz
X1
X2
8.192kHz
32.768kHz
1Hz/4.096kHz
ALARM/
WATCHDOG
STAT/CTRL/
TRICKLE
24-BIT
COUNTER
INT
CONTROL
RST
CONTROL
2-WIRE
INTERFACE
POWER
CONTROL
AND
TRICKLE
CHARGE
V
CC
V
BACKUP
GND
SDA
SCL
RST
SQW
INT
DS1374
Figure 4. Functional Diagram
Detailed Description
The DS1374 is a real-time clock with an I
2
C serial inter-
face. It provides elapsed seconds from a user-defined
starting point in a 32-bit counter (Figure 4). A 24-bit
counter can be configured as either a watchdog
counter or an alarm counter. An on-chip oscillator cir-
cuit uses a customer-supplied 32.768kHz crystal to
keep time. A power-control circuit switches operation
from V
CC
to V
BACKUP
and back when power on V
CC
is
cycled. The oscillator and counters continue to operate
when powered by either supply. If a rechargeable
backup supply is used, a trickle charger can be
enabled to charge the backup supply while V
CC
is on.
Oscillator Circuit
The DS1374 uses an external 32.768kHz crystal. The
oscillator circuit does not require any external resistors
or capacitors to operate. Table 1 specifies several crys-
tal parameters for the external crystal. Figure 5 shows a
functional schematic of the oscillator circuit. The startup
time is usually less than 1 second when using a crystal
with the specified characteristics.
Clock Accuracy
Clock accuracy is dependent upon the accuracy of the
crystal and the accuracy of the match between the
capacitive load of the oscillator circuit and the capacitive
load for which the crystal was trimmed. Additional error
is added by crystal frequency drift caused by tempera-
ture shifts. External circuit noise coupled into the oscilla-
tor circuit can result in the clock running fast. Figure 6
shows a typical PC board layout for isolating the crystal
and oscillator from noise. Refer to
Application Note 58:
Crystal Considerations with Dallas Real-Time Clocks
for
detailed information.
DS1374C Only
The DS1374C integrates a standard 32,768Hz crystal
into the package. Typical accuracy at nominal V
CC
and
25°C is approximately 10ppm. See
Application Note 58
for information about crystal accuracy vs. temperature.
DS1374
I
2
C, 32-Bit Binary Counter Watchdog RTC with
Trickle Charger and Reset Input/Output
_____________________________________________________________________ 9
COUNTDOWN
CHAIN
X1
X2
C
L
1
C
L
2
CRYSTAL
RTC
REGISTERS
DS1374
Figure 5. Oscillator Circuit Showing Internal Bias Network
LOCAL GROUND PLANE (LAYER 2)
NOTE: AVOID ROUTING SIGNALS IN THE CROSSHATCHED AREA (UPPER LEFT-HAND
QUADRANT) OF THE PACKAGE UNLESS THERE IS A GROUND PLANE BETWEEN THE
SIGNAL LINE AND THE PACKAGE.
CRYSTAL
GND
X2
X1
Figure 6. Layout Example
PARAMETER SYMBOL MIN TYP MAX UNITS
Nominal
Frequency
f
O
32.768 kHz
Series
Resistance
ESR 45 kΩ
Load
Capacitance
C
L
6pF
Table 1. Crystal Specifications*
*
The crystal, traces, and crystal input pins should be isolated
from RF generating signals. Refer to
Application Note 58:
Crystal Considerations for Dallas Real-Time Clocks
for addi-
tional specifications
.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18

DS1374C-3#

Mfr. #:
Buy DS1374C-3#
Manufacturer:
Maxim Integrated
Description:
Real Time Clock I2C 32-Bit Binary Counter Watchdog
Lifecycle:
New from this manufacturer.
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