MIC2205 Evaluation Board High Efficiency 2Mhz Step-Down Converter with LOW Mode General Description Precautions The evaluation board does not have reverse polarity The Micrel MIC2205 is a high efficiency 2MHz PWM protection. Applying a negative voltage to the VIN synchronous step-down switching regulator that terminal may damage the device. features a LOWQ LDO standby mode that draws only 18A of quiescent current. The MIC2205 In addition, the maximum operating voltage of the features an ultra-low noise, small size, and high MIC2205 evaluation board is 5.5V. Exceeding 6V on efficiency solution for portable power applications. the input could damage the device. In PWM mode, the MIC2205 operates at a constant Getting Started frequency of 2MHz. Under light load conditions, such 1. Connect an external supply to V as in system sleep or standby modes, the PWM IN terminal. Apply desired input voltage to the switching operation can be disabled to reduce V and ground terminals of the evaluation switching losses. In this light load LOWQ mode, the IN board, paying careful attention to polarity LDO maintains the output voltage and draws only and supply voltage (2.7V V 5.5V). An 18A of quiescent current. The LDO mode of IN ammeter may be placed between the input operation saves battery life while not introducing supply and the V terminal to the evaluation spurious noise and high ripple as experienced with IN board. Be sure to monitor the supply voltage pulse skipping or bursting mode regulators. at the V terminal. The ammeter and/or IN The MIC2205 operates from a 2.7V to 5.5V input and power lead resistance can reduce the features internal power MOSFETs that can supply up voltage supplied to the input. to 600mA of output current in PWM mode. It can 2. Connect the load to the V and ground OUT operate with a maximum duty cycle of 100% for use terminals. The load can be either passive in low-dropout conditions. (resistive) or active (electronic load). An Requirements ammeter can be placed between the load and the V terminal. Ensure the output OUT The MIC2205 evaluation board requires an input voltage is monitored at the V terminal. OUT power source that is able to deliver greater than 1A at The default output voltage is set to 1.8V. 2.7V. The output load can either be an active or This can be adjusted by changing the passive source. feedback resistors. (see Output Voltage). 3. Enable the MIC2205. Apply a 1.3V or greater voltage source to the enable pin. LOWQ 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 MIC2205 Evaluation Board TM Output Voltage LOWQ The output voltage on the MIC2205 evaluation board The MIC2205 is a 600mA PWM power device that is adjustable. The output voltage is controlled by the utilizes a LOWQ light load mode to maximize feedback resistors (R1 and R2) and can be battery efficiency in light load conditions. This is calculated as follows: achieved with a LOWQ control pin that when pulled low, (Remove JP1), shuts down all the biasing and R1 drive current for the PWM regulator, drawing only V = 1.0V + 1 OUT 18A of operating current. This allows the output to R2 be regulated through the LDO output that is capable of providing 60mA of output current. This method has The evaluation board is initially adjusted to 1.8V, but the advantage of producing a clean, low current, ultra can easily be modified by removing R2 and low noise output in LOWQ mode. During LOWQ replacing it with the value that yields the desired mode, the SW node becomes high impedance, output voltage. (Removing R2 sets the output to blocking current flow. Other methods of reducing 1.0V). quiescent current, such as pulse frequency modulation (PFM) or bursting techniques, create large 100k R2 = amplitude, low frequency ripple voltages that can be V OUT detrimental to system operation. 1 1.0V When more than 60mA is required, the LOWQ pin can be forced high, (Connect JP1), causing the MIC2205 to enter PWM mode. In this case, the LDO output makes ahand-of to the PWM regulator virtually without any variation in output voltage. The LDO output then turns off allowing up to 600mA of current to be efficiently supplied through the PWM output to the load. 2 May 2006 M9999-051606 (408) 955-1690