MIC23099 Evaluation Board Single AA/AAA Cell Step-Up/Step-Down Regulators with Battery Monitoring General Description Getting Started The MIC23099 is a high-efficiency, low-noise, dual-output, 1. VIN Supply integrated power-management solution for single-cell Connect a supply to the VIN and GND terminals, alkaline or NiMH battery applications. The synchronous paying careful attention to the polarity and the supply boost output voltage (V ) is enabled first and is OUT1 range (0V < VIN < 1.6V). Do not apply power until step powered from the battery. Next, the synchronous buck 4. output (V ) which is powered from the boost output OUT2 2. Connect Load and Monitor Output voltage is enabled. This configuration allows V to be OUT2 independent of battery voltage, thereby allowing the buck Connect a load to the VOUT1 and VOUT2 and GND output voltage to be higher or lower than the battery terminals. The load can be either a passive (resistive) voltage. or an active (as in an electronic load) type. A current meter may be placed between the output terminals To minimize switching artifacts in the audio band, both the and load to monitor the output current. Ensure that the converters are design to operate with a minimum switching output voltage is monitored at the output terminals. frequency of 80kHz for the buck and 100kHz for the boost. The high current boost has a maximum switching 3. Enable Input frequency of 1MHz, minimizing the solution foot-print. The EN pin has an internal 4M pull-down resistor to GND, which allows the output to be turned off when The MIC23099 incorporates both battery-management the EN jumper is removed. Applying an external logic functions and fault protection. The low-battery level is signal on the EN pin to pull it high or using a jumper to indicated by an external LED connected to the LED pin. In short the EN pin to VIN to turn the outputs on. addition, a supervisory circuit monitors each output and asserts a power-good (PG) signal when the sequencing is 4. Turn Power done or de-asserted when a fault condition occurs. Turn on the VIN supply and verify that the output The basic parameters of the evaluation board are: voltages VOUT1 = 1.8V and VOUT2 = 1.0V. 5. Power Good Output Input: 0.85V to 1.6V This is on open drain output that is pulled high when Output 1: 1.8V/0.2A V , V and V are within their nominal voltage IN FB1 FB2 Output 2: 1.0V/30mA levels. The power good will be pulled low without delay when the enable pin is set low. Datasheets and support documentation are available on 6. LED Output Micrels web site at: www.micrel.com. This is an open drain output that is used for a low battery indicator. Under normal conditions, the LED is Requirements always ON. If the battery voltage is between 1.2V to The MIC23099 evaluation board requires only a single 0.85V, the external LED will blink with a duty cycle of power supply with at least 1A current capability. The 25% at 0.25Hz. The LED will be OFF if the battery output load can either be an active (electronic) or passive voltage falls below 0.85V for more than 15 cool-off (resistive) load. cycles or the EN pin is low. Precautions 7. SW1 and SW2 Test Points The MIC23099 evaluation board does not have reverse These are switch node test points. polarity protection. Applying a negative voltage to the VIN and GND terminals may damage the device. The Ordering Information maximum operating rating for V is 1.6V. Exceeding 1.6V IN on the VIN could damage the device. Part Number Description MIC23099YFT EB MIC23099 Evaluation Board HyperLight Load is a registered trademark and Hyper Speed Control is a trademark of Micrel, Inc. Micrel Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel +1 (408) 944-0800 fax + 1 (408) 474-1000 Micrel, Inc. MIC23099 Evaluation Board Evaluation Board Features Feedback Resistors Buck Switching Frequency An external resistive divider network (R1 and R2) with its The buck converter is designed to operate in PFM mode center tap connected to the feedback pin sets the output only. It has peak current control, which turns off the high- voltage for each regulator. R1 is the top resistor and R2 is side switch when the inductor current hits the current limit the bottom resistor in the divider string. The resistor values threshold. The cycle repeats itself when the output voltage for the desired output voltage are calculated as illustrated falls below its regulated value. As a result, the switching in Equation 1. Large resistor values are recommended to frequency varies linearly with output current as shown in reduce light load operating current, and improve efficiency. Figure 2. The buck switching frequency is greater than The recommended resistor value for R1 should be around, 80kHz with loads greater than 8mW. R1 400k. R1 R2 = Eq. 1 V OUT 1 0.6V In the case of the boost converter, Equation 1 sets the output voltage to its PWM value. The no-load PFM output voltage is 2% higher than the PWM value. This higher PFM output voltage value is necessary to prevent PFM to PWM mode skipping which can introduce noise into the audio band. Boost Switching Frequency Figure 2. Buck Switching Frequency vs. Output Current To reduce switching artifacts in the audio band, the buck and boost regulators switching frequency are controlled to minimize overlap. Figure 1 shows the boost switching Power Good frequency versus output load current and Figure 2 shows The power good (PG) circuitry monitors the battery voltage the buck switching frequency versus output load current. and feedback pin voltage of the boost and buck regulators. The boost regulator operates in either PWM or PFM mode. The PG pin output goes logic high when FB1 and FB2 pin To avoid PWM to PFM chatter, the PWM entry and exit voltages are both greater than 92.5% (typical) of the points are not the same. When in PFM mode the output internal reference voltage and the input voltage is greater current needs to reach 90mA to enter into PWM mode and than 0.85V (typical). To minimize false triggering, the exits at 30mA. The boost switching frequency is greater power-good output has both a turn on delay and a falling than 100kHz with loads greater than 20mW. deglitch delay. Figure 1. Boost Switching Frequency vs. Output Current Revision 1.0 May 30, 2014 2