DS1374U-3+ Maxim Integrated Products, DS1374U-3+ Datasheet - Page 13

• Manufacturer Part Number: DS1374U-3+
• Description: IC RTC I2C W/CHARGER 10-USOP
• Manufacturer: Maxim Integrated Products
• Type: Watchdog Timer/Trickle Chargerr

Specifications of DS1374U-3+

• Time Format: Binary
• Date Format: Binary
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 2.7 V ~ 3.3 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Memory Size: -

Bit 7/Oscillator Stop Flag (OSF). A logic 1 in this bit
indicates that the oscillator either is stopped or was
stopped for some period of time and can be used to
judge the validity of the timekeeping data. This bit is set
to logic 1 any time the oscillator stops. The following
are examples of conditions that can cause the OSF bit
to be set:
1) The first time power is applied.
2) The voltage present on both V
3) The EOSC bit is turned off.
4) External influences on the crystal (i.e., noise, leak-
This bit remains at logic 1 until written to logic 0.
Bit 0/Alarm Flag (AF). A logic 1 in the alarm flag bit
indicates that the WD/ALM counter reached zero. If
WD/ALM is set to zero and the AIE bit = 1, the INT pin
goes low and stays low until AF is cleared. AF is
cleared when written to logic 0. This bit can only be
written to logic 0. Attempting to write logic 1 leaves the
value unchanged. If WD/ALM is set to 1 and the AIE
bit = 1, the INT pin pulses low for 250ms when the
WD/ALM counter reaches zero and sets AF = 1. At the
pulse completion, the DS1374 clears the AF bit to zero.
If the 250ms pulse is active, writing AF to zero does not
truncate the pulse.
The simplified schematic in Figure 7 shows the basic
components of the trickle charger. The trickle-charge
Table 5. Trickle Charge Register
TCS3
insufficient to support oscillation.
age, etc.).
X
X
X
1
1
1
1
1
1
0
Bit 7
OSF
I
2
TCS2
C, 32-Bit Binary Counter Watchdog RTC with
X
X
X
0
0
0
0
0
0
0
Trickle-Charge Register (10h)
Bit 6
0
TCS1
Trickle Charger and Reset Input/Output
X
X
X
1
1
1
1
1
1
0
Status Register (08h)
CC
Bit 5
0
TCS0
and V
____________________________________________________________________
X
X
X
0
0
0
0
0
0
0
BACKUP
DS1
Bit 4
0
1
X
0
1
0
1
0
1
0
0
are
DS0
X
0
1
1
0
1
0
1
0
0
select (TCS) bits (bits 4–7) control the selection of the
trickle charger. To prevent accidental enabling, only a
pattern of 1010 enables the trickle charger. All other
patterns disable the trickle charger. The trickle charger
is disabled when power is first applied. The diode
select (DS) bits (bits 2, 3) select whether or not a diode
is connected between V
no diode is selected; if DS is 10, a diode is selected.
The ROUT bits (bits 0, 1) select the value of the resistor
connected between V
the resistor selected by the resistor select (ROUT) bits
and the diode selected by the diode select (DS) bits.
Warning: The ROUT value of 250Ω must not be select-
ed whenever V
The user determines diode and resistor selection
according to the maximum current desired for battery or
super cap charging. The maximum charging current can
be calculated as illustrated in the following example.
Assume that a system power supply of 3.3V is applied
to V
assume the trickle charger has been enabled with a
diode and resistor R2 between V
maximum current I
as follows:
As the super cap changes, the voltage drop between
V
current decreases.
I
CC
MAX
Bit 3
CC
0
and V
= (3.3V - diode drop) / R2 ≈ (3.3V - 0.7V) / 2kΩ ≈
and a super cap is connected to V
ROUT1
X
X
0
0
0
1
1
1
1
0
BACKUP
CC
Bit 2
is greater than 3.63V.
0
ROUT0
decreases and therefore the charge
MAX
X
X
0
1
1
0
0
1
1
0
CC
would therefore be calculated
1.3mA
CC
and V
and V
Disabled
Disabled
Disabled
No diode, 250Ω resistor
One diode, 250Ω resistor
No diode, 2kΩ resistor
One diode, 2kΩ resistor
No diode, 4kΩ resistor
One diode, 4kΩ resistor
Power-on reset value
BACKUP
Bit 1
CC
0
BACKUP
and V
FUNCTION
. Table 5 shows
BACKUP
. If DS is 01,
BACKUP
Bit 0
AF
. Also
. The
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