Using ISL12058 as a Low Cost Alternative to ISL1208 and ISL12082 ® Technical Brief Introduction Intersil has recently introduced the ISL12058 Real Time Clock (RTC) devices. The ISL12058 is a basic RTC that provides: • Real Time Clock/Calendar - Tracks Time in Hours, Minutes, and Seconds - Day of the Week, Date, Month, and Year June 9, 2009 TB481.0 example circuit with VDD to 3.3V, and I2C lines and IRQx pulled 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 3 shows an example circuit with a Zener diode to lower the 5.5V input voltage to 3.3V for VDD. • No ATR and DTR registers for oscillator frequency trimming • 4 Selectable Frequency Outputs • Alarm Function • 4 Package Options - 2mmx2mm µTDFN - 3mmx3mm TDFN - 8 Ld SOIC - 8 Ld MSOP The features are detailed in the data sheets. This Technical Brief provides information for an engineer wishing to use the ISL12058 as an alternative replacement for the ISL1208 and ISL12082. Advantages and Disadvantages of Replacing the ISL1208 with the ISL12058 Things to consider if you wish to replace the ISL1208 with the ISL12058. • 4 selectable frequency outputs and slight software change to select frequency output - ISL12058: The 4 selectable frequency outputs are 32.768kHz, 8.192kHz, 4.096kHz and 1Hz. The two FO bits to select the frequency outputs are located at bit 4 and 3 in address 08h. - ISL1208: 15 selectable frequency outputs. The four FO bits to select the frequency outputs are located at bit 3, 2, 1 and 0 in address 08h. • Slight software change for Alarm1 interrupt on IRQ/FOUT pin - ISL12058: To enable Alarm1 interrupt on IRQ/FOUT pin, IRQE and A1E bits in address 08h have to be set to “1”. - ISL1208: To enable Alarm interrupt on IRQ/FOUT pin, all the FO3, FO2, FO1, and FO0 bits in address 08h have to be set to “0”. • No IM bit to enable the Alarm’s Repetitive/Recurring Time Event. ADVANTAGES: • Lower operating current (500nA vs 1.2µA @ VDD = 3.0V) BAT54C • Lower VDD operating range (1.4V vs 2.7V) ISL12058 VIN = 3.3V • Dual Alarms with every second interrupt on Alarm1 and every minute interrupt on Alarm2. • Same RTC registers setup and similar Control and Status register setup VDD 0.1µF VBAT = 3V GND • Smaller package option (µTDFN)) • Lower cost FIGURE 1. EXAMPLE CIRCUIT FOR SYSTEM REQUIRING BATTERY BACK-UP BY USING BAT54C ON VDD DISADVANTAGES: 0.1µF VDD 10kΩ 1 ISL12058 VDD = 3.3V 10kΩ • Maximum VDD operating voltage is 3.6V - 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 2 shows an VPULLUP = 5.5V 10kΩ • No battery backup - A system requiring battery backup can implement a slight hardware change and use a BAT54C Schottky Diode on VDD to accept a regular input voltage and battery voltage. Figure 1 shows the example circuit of using the BAT54C on VDD. SDA SCL IRQx GND FIGURE 2. EXAMPLE CIRCUIT WITH VDD AT 3.3V AND I2C AND IRQX PULLED UP TO 5.5V 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 481 VPULLUP = 5.5V 10kΩ VDD 0.1µF 10kΩ 3.3V Zener ISL12058 VDD = 3.3V 10kΩ VIN = 5.5V 55kΩ SDA SCL IRQx GND FIGURE 3. EXAMPLE CIRCUIT WITH ZENER DIODE ON VDD TO REDUCE INPUT VOLTAGE TO 3.3V Advantages and Disadvantages of Replacing the ISL12082 with the ISL12058 circuit with a Zener diode to lower the 5.5V input voltage to 3.3V for VDD. • One Interrupt Output for Alarm Interrupt and Frequency Output - IRQ/FOUT is available for alarm interrupt and frequency output. - IRQ2 is not available in ISL12058. • Requires Hardware Change for pin-to-pin Compatibility - 8 Ld SOIC: Relocating GND pin to pin 4 to match ISL12058 pinout. - 10 Ld MSOP: Removing pin 5 and 6 to match ISL12058 pinout. • No Timer feature Things to consider if you wish to replace the ISL12082 with the ISL12058. • No ATR and DTR Registers for Oscillator Frequency Trimming ADVANTAGES: • No Sub-Second feature • Lower Operating Current (500nA vs 1.6µA @ VDD = 3.0V) • Slight Software Change for Alarm1 Interrupt on IRQ/FOUT Pin - ISL12058: To enable Alarm1 interrupt on IRQ/FOUT pin, the IRQE and A1E bits in address 08h have to set to “1”. - ISL12082: To enable Alarm interrupt on IRQ/FOUT pin, IRQ1E bit in address 08h has to set to “1”. • Lower VDD Operating Range (1.4V vs 2.7V) • Dual Alarms with every Second Interrupt on Alarm1 and every Minute Interrupt on Alarm2. • Same RTC Registers Set-up and Similar Control and Status Register Set-up • Smaller Package Option (µTDFN)) • No IM Bit to Enable the Alarm’s Repetitive/Recurring Time Event. ISL12082 10 LD MSOP ISL12082 8 LD SOIC • Lower Cost DISADVANTAGES: • No Battery Backup - 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 1 shows the example circuit of using the BAT54C on VDD. • Maximum VDD Operating Voltage is 3.6V - 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 2 shows an example circuit with VDD to 3.3V and I2C lines and IRQx pulled up to 5.5V. - A system that cannot connect VDD to voltage lower than 3.6V can use a Zener diode on the VDD pin to lower the VDD to 3.6V or below. Figure 3 shows an example X1 1 8 VDD X1 1 10 X2 2 7 IRQ1/FOUT X2 2 9 IRQ1/FOUT VDD GND 3 6 SCL VBAT 3 8 SCL IRQ2 4 5 SDA GND 4 7 SDA NC 5 6 IRQ2 ISL12058 8 LD SOIC/MSOP X1 1 8 VDD X2 2 7 IRQ/FOUT NC 3 6 SCL GND 4 5 SDA FIGURE 4. PINOUTS OF ISL12058’s 8 LD SOIC AND MSOP PACKAGES AND ISL12082’s 8 LD SOIC AND 10 LD MSOP PACKAGES 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 TB481.0 June 9, 2009