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Replacing the M41T00S and DS1340
RTC with the ISL12059
®
Technical Brief
Introduction
Intersil has recently introduced the ISL12059 Real Time
Clock (RTC) device. The device is pin-to-pin, and software
compatible to the STMicro M41T00S and Maxim DS1340
RTCs. The ISL12059 has some advantages against the
M41T00S and DS1340. These advantages include:
• Lower Operating, Standby and Timekeeping Current
• Power Failure Indictor
This Technical Brief provides information for an engineer
wishing to use the ISL12059 to replace the M41T00S or
DS1340 in their system.
Replacing the M41T00S with the ISL12059
The ISL12059 can drop into an M41T00S socket with no
hardware and software changes required.
There are two differences that may affect hardware
requirements. First, the M41T00S can operate at VDD up to
5.5V, while the ISL12059 has an operating range of up to
3.6V. The ISL12059 allows SDA, SCL, FT/OUT to be pulled
up to 5.5V.
A system that has the I2C lines pulled up to 5.5V (or other
voltage higher than 3.6V), but has a 3.3V regulator on board
requires a simple modification to connect the VDD to 3.3V
instead of 5.5V. Figure 1 shows an example circuit with VDD
to 3.3V and I2C lines and FT/OUT pull-up to 5.5V
A system that cannot connect VDD to a voltage lower than
3.6V can use a Zener diode on the VDD pin to lower the VDD
to 3.6V or below. Figure 2 shows an example circuit with
Zener diode to lower the 5.5V input voltage to 3.3V for VDD.
The second difference that may affect hardware requirement
is the ISL12059 does not offer battery back-up. A system
requiring battery back-up can implement a slight hardware
change, and use a BAT54C Schottky Diode on VDD to
accept a regular input voltage and battery voltage. Figure 3
shows the example circuit of using the BAT54C on VDD.
The DS1340 has battery charging function, and the
ISL12059 does not provide battery charging function.
VPULLUP = 5.5V
0.1µF
VDD
10kΩ
VDD = 3.3V
SDA
SCL
FT/OUT
GND
FIGURE 1. EXAMPLE CIRCUIT WITH VDD AT 3.3V AND I2C
AND IRQX PULL-UP TO 5.5V
VPULLUP = 5.5V
0.1µF
3.3V Zener
VDD
10kΩ
VDD = 3.3V
10kΩ
VIN = 5.5V 55kΩ
10kΩ
The second difference that may affect hardware
requirements is the ISL12059 does not offer battery back-up.
A system requiring battery back-up can implement a slight
hardware change and use a BAT54C Schottky Diode on
VDD to accept a regular input voltage and battery voltage.
Figure 3 shows the example circuit of using the BAT54C on
VDD.
while the ISL12059 has an operating range up to 3.6V. The
ISL12059 allows SDA, SCL, FT/OUT pull-up to 5.5V.
10kΩ
A system that cannot connect VDD to a voltage lower than
3.6V can use a Zener diode on the VDD pin to lower the VDD
to 3.6V or below. Figure 2 shows an example circuit with a
Zener diode to lower the 5.5V input voltage to 3.3V for VDD.
TB482.0
10kΩ
A system that has the I2C lines pulled up to 5.5V (or other
voltage higher than 3.6V), but has a 3.3V regulator on board
requires a simple modification to connect the VDD to 3.3V,
instead of 5.5V. Figure 1 shows an example circuit with
VDD = 3.3V and the I2C lines and FT/OUT pulled up to 5.5V
June 12, 2009
SDA
SCL
FT/OUT
GND
Replacing the DS1340 with the ISL12059
The ISL12059 can drop into an DS1340 8 Ld SOIC socket with
no hardware and software changes required.
FIGURE 2. EXAMPLE CIRCUIT WITH ZENER DIODE ON VDD
TO REDUCE INPUT VOLTAGE TO 3.3V
There are three differences that may affect hardware
requirements.
First, the DS1340 offers three subsets that operate at
different voltage levels. These voltage levels are: 1.8V, 3V
and 3.3V. The ISL12059 can replace the 1.8V, 3V and 3.3V
options. The 3.3V option can operate at VDD up to 5.5V,
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CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2009. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Technical Brief 482
BAT54C
ISL12059
VIN = 3.3V
VDD
0.1µF
VBAT =3V
GND
FIGURE 3. EXAMPLE CIRCUIT FOR SYSTEM REQUIRING BATTERY BACKUP BY USING BAT54C ON VDD
TABLE 1. REPLACING THE M41T00S AND DS1340 WITH ISL12059
M41T00S
FUNCTION
MIN
Supply Voltage
TYP
2.7V
DS1340-3
MAX
MIN
5.5V
2.7V
TYP
M41T00S
MAX
MIN
3.3V
1.4V
TYP
MAX
AFFECTS SOFTWARE?
3.6V
NO
Operating Current
300µA
108µA
200µA
15µA
40µA
NO
Standby Current
70µA
81µA
125µA
0.5µA
0.95µA
NO
1µA
0.8µA
1µA
0.6µA
0.95µA
NO
Timekeeping Current @ 3.3V
0.8µA
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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June 12, 2009