MIC23250 Evaluation Board 4MHz Dual 400mA Synchronous Buck Regulator with HyperLight Load may be placed between the input supply and the General Description V (J1) terminal to the evaluation board. Be sure IN The MIC23250 is a dual 400mA 4MHz switching regulator to monitor the supply voltage at the V (J1) IN with HyperLight Load mode. The MIC23250 is highly terminal, as the ammeter and/or power lead efficient, consuming 33A of quiescent current to operate resistance can reduce the voltage supplied to the both of its outputs. A Sub-1mm height solution is easily input. attainable using the tiny package (2mm x 2mm x 0.55mm) and only six external components. Small and fast, the 2. Connect a load to the V 1 (J4) and V 2 (J6) O O MIC23250 can respond to a load transient at ultra-fast outputs and ground terminal (J7). The loads speed while reducing output peak-to-peak voltage. can be either passive (resistive) or active (electronic load). An ammeter can be placed The MIC23250 has two modes of operation that is between the load and the output terminal. Ensure automatically selected by the internal circuitry. Under light that the output voltages are monitored at the V 1 O load conditions, the MIC23250 goes into HyperLight (J4) and V 2 (J6) terminals. O Load mode. The MIC23250 HyperLight Load uses a Pulse-Frequency Modulation (PFM) control scheme that 3. Enable the MIC23250 outputs. The MIC23250 controls the off time at light load. This allows the device to evaluation board has pre-installed pull-up resistors reduce the amount of switching needed at light load, thus (R1 and R2) that enable the device as soon as reducing the switching losses. The MIC23250 can attain input voltage is applied. These resistors are up to 85% efficiency at 1mA output load. At higher output optional. To disable the device, apply a voltage currents of approximately 100mA, HyperLight Load below 0.5V to EN1 (J3) or EN2 (J5) terminals. mode automatically switches back to Pulse-Width Similarly, if the pull up resistors (R1 and R2) are Modulation (PWM) mode to ensure high efficiency up to not used the device may be enabled by applying a 94% at higher load. The two modes of operation ensure voltage greater than 1.2V to the EN1 (J3) or EN2 that the MIC23250 maintains the highest efficiency (J5) terminals. Be sure that the enable voltage throughout the entire load range. never exceeds the input voltage. The MIC23250 operates from a 2.7V to 5.5V input and features internal power MOSFETs that can supply up to Output Voltage 400mA of output current on each channel. It can operate The MIC23250 evaluation board has fixed output voltage with a maximum duty cycle of 90%. options available per the table below. Requirements The MIC23250 evaluation board requires an input power Ordering Information source that is able to deliver greater than 800mA at 2.7V. Part Number Description The output loads can either be an active (electronic) or passive (resistive) load. MIC23250-C4YMT EV 1.2V / 1.0V Output Evaluation Board MIC23250-G4YMT EV 1.2V / 1.8V Output Evaluation Board Getting Started MIC23250-S4YMT EV 1.2V / 3.3V Output Evaluation Board 1. Connect an external supply to the V (J1) IN MIC23250-AAYMT EV Adjustable Output Evaluation Board terminal. Apply desired input voltage to the V IN (J1) and ground (J2) terminal of the evaluation Note: Other voltage options available upon request. Contact Micrel. board, paying careful attention to polarity and supply voltage (2.7V < V < 5.5V). An ammeter IN HyperLight Load 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. MIC23250 Evaluation Board Feedback Resistor Selection (Adjustable Only) The feedback pins (FB1/FB2) are two extra pins that can V (V) R (k ) R (k ) CFF (pF) OUT TOP BOTTOM only be found on the MIC23250-AAYMT devices. It 0.8 49 442 120 allows the regulated output voltage to be set by applying an external resistor network. The internal reference 0.9 111 442 120 voltage is 0.72V and the recommended value of R BOTTOM 1 172 442 120 is within 10% of 442k . The R resistor is the resistor TOP 1.1 233 442 120 from the FB pin to the output of the device and R BOTTOM is the resistor from the FB pin to ground. The output 1.2 295 442 120 voltage is calculated from the equation below. 1.3 356 442 120 R TOP 1.4 417 442 120 V = 0.72V + 1 OUT R BOTTOM 1.5 479 442 120 1.6 540 442 120 Compensation 1.7 602 442 120 The MIC23250 is designed to be stable with a 0.47H to 4.7H inductor with a minimum of 2.2F ceramic (X5R) 1.8 663 442 120 output capacitor. For the adjustable MIC23250, the total 1.9 724 442 120 feedback resistance should be kept as high as possible to reduce current loss down the feedback resistor 2 786 442 120 network. This helps to improve efficiency. A feed-forward 2.1 847 442 120 capacitor (CFF) of 120pF must be used in conjunction 2.2 909 442 120 with the external feedback resistors to reduce the effects of parasitic capacitance that is inherent of most circuit 2.3 970 442 120 board layouts. Figure 1 and Table 1 shows the 2.4 1031 442 120 recommended feedback resistor values along with the recommended feed-forward capacitor for the MIC23250 2.5 1093 442 120 adjustable device. 2.6 1154 442 120 2.7 1216 442 120 R C 2.8 1277 442 120 TOP FF 2.9 1338 442 120 3 1400 442 120 R 3.1 1461 442 120 BOTTOM 3.2 1522 442 120 3.3 1584 442 120 Figure 1. Feedback Resistor Network Table 1. Recommended Feedback Component Values For V 1 the feedback components are: R = R3, O TOP R = R4, C = C5. For V 2 the feedback BOTTOM FF O components are: R = R5, R = R6, C = C6. TOP BOTTOM FF July 2009 2 M9999-070909-C