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, 1 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 2 TB482.0 June 12, 2009