MIC3385 Evaluation Board High Efficiency 8MHz Step-Down Converter with LOWQ® Mode General Description The Micrel MIC3385 is a high efficiency 8MHz PWM synchronous step-down switching regulator that features a LOWQ® LDO standby mode that draws only 20µA of quiescent current. The MIC3385 features an ultra-low noise, small size, and high efficiency solution for portable power applications. In PWM mode, the MIC3385 operates at a constant frequency of 8MHz. Under light load conditions, such as in system sleep or standby modes, the PWM switching operation can be disabled to reduce switching losses. In this light load LOWQ® mode, the LDO maintains the output voltage and draws only 20µA of quiescent current. The LDO mode of operation saves battery life while not introducing spurious noise and high ripple as experienced with pulse skipping or bursting mode regulators. The MIC3385 operates from a 2.7V to 5.5V input and features internal power MOSFETs that can supply up to 600mA of output current in PWM mode. It can operate with a maximum duty cycle of 100% for use in low-dropout conditions. Requirements The MIC3385 evaluation board requires an input power source that is able to deliver greater than 600mA at 2.7V. The output load can either be an active or passive source. Precautions The evaluation board does not have reverse polarity protection. Applying a negative voltage to the VIN terminal may damage the device. In addition, the maximum operating voltage of the MIC3385 evaluation board is 5.5V. Exceeding 6V on the input could damage the device. Getting Started 1. Connect an external supply to VIN terminal. Apply desired input voltage to the VIN (J1)and ground (J2 and J6) terminals of the evaluation board, paying careful attention to polarity and supply voltage (2.7V≤VIN≤5.5V). An ammeter may be placed between the input supply and the VIN terminal to the evaluation board. Be sure to monitor the supply voltage at the VIN terminal. The ammeter and/or power lead resistance can reduce the voltage supplied to the input. 2. Connect the load to the VOUT (J5) and ground terminals. The load can be either passive (resistor) or active (electronic load). An ammeter can be placed between the load and the VOUT terminal. Be sure to monitor the output voltage at the VOUT terminal. The default output voltage is set to 1.8V. This can be adjusted by changing the feedback resistors. (see Output Voltage). 3. Disable the MIC3385. Apply ground, or 0V, to the enable (EN) J4 terminal. LOWQ is a registered trademark of Micrel, Inc. Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax 1 (408) 474-1000 • http://www.micrel.com November 2007 M9999-110607-B Micrel, Inc. MIC3385 Evaluation Board providing 60mA of output current. This method has the advantage of producing a clean, low current, ultra low noise output in LOWQ® mode. During LOWQ®mode, the SW node becomes high impedance, blocking current flow. Other methods of reducing quiescent current, such as pulse frequency modulation (PFM) or bursting techniques, create large amplitude, low frequency ripple voltages that can be detrimental to system operation. When more than 60mA is required, the LOWQ pin can be forced high, (Connect JP1), causing the MIC3385 to enter PWM mode. In this case, the LDO output makes a "hand-off" 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. Output Voltage The output voltage on the MIC3385 evaluation board is adjustable. The output voltage is controlled by the feedback resistors (R1 and R2) and can be calculated as follows: R1 + 1) VOUT = 1.0V x ( R2 The evaluation board is initially adjusted to 1.8V, but can easily be modified by removing R2 and replacing it with the value that yields the desired output voltage. (Removing R2 sets the output to 1.0V). R2 = ( VOUT 1.0V - 1) LOWQ® The MIC3385 is a 600mA PWM power device that utilizes a LOWQ® light load mode to maximize battery efficiency in light load conditions. This is achieved with a LOWQ® control pin that when pulled low, (Remove JP1), shuts down all the biasing and drive current for the PWM regulator, drawing only 20µA of operating current. This allows the output to be regulated through the LDO output that is capable of November 2007 Ordering Information 2 Part Number Description MIC3385 EV Evaluation board with the MIC3385-YHL device M9999-110607-B Micrel, Inc. MIC3385 Evaluation Board U1 MIC3385-YHL VIN 2 J1 VIN 5.5V Max C1 10µF 6.3V 12 VIN AVIN 1 R4 10K 2 JP1 1X2 J4 EN J3 LOWQ 4 3 VIN VO VO VO 7 6 5 SW SW SW 10 9 8 LDO 13 EN C4 10µF 6.3V R1 Option LOWQ FB GND BIAS C3 82pF 50V 1 R3 14 J5 VO 11 R2 Option C2 0.1µF 6.3V J6 GND J2 GND Bill of Materials Ref Des C1, C4 C2 C3 R1 R2 R3 R4, R5 U1 Part Number C1608X5R0J106K 06036D106MAT2A GRM188R60J106M C1005X5R0J104M 04026D104MAT2A GRM155R60J104K VJ0402A820KXQCW1BC C1005COG1H820J CRCW04021003F CRCW04021243F CRCW040220R0F CRCW04021002F MIC3385YHL Description 10µF 6.3V X5R 0603 Ceramic Capacitor 10µF 6.3V X7R 0603 Ceramic Capacitor 0.1µF 6.3V X5R 0402 Ceramic Capacitor 0.1µF 6.3V X7R 0402 Ceramic Capacitor 82pF X7R 0402 Ceramic Capacitor 82pF COG 0402 Ceramic Capacitor 100kΩ 1% 0402 Resistor (Optional) 124kΩ 1% 0402 Resistor (Optional) 20Ω 1% 0402 Resistor 10kΩ 1% 0402 Resistor 8MHz PWM Step-Down Converter/LDO Manufacturer TDK(1) AVX(2) MuRata(3) TDK(1) AVX(2) MuRata(3) Vishay(4) TDK(1) Vishay(4) Vishay(4) Vishay(4) Vishay(4) Micrel, Inc.(5) Notes: 1. TDK: www.tdk.com 2. AVX: www.avx.com 3. Murata: www.murata.com 4. Vishay: www.vishay.com 5. Micrel, Inc.: www.micrel.com November 2007 3 M9999-110607-B Micrel, Inc. MIC3385 Evaluation Board Printed Circuit Board Layouts Figure 1a. Top Layer Figure 1b. Bottom Layer November 2007 4 M9999-110607-B Micrel, Inc. MIC3385 Evaluation Board MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2007 Micrel Incorporated November 2007 5 M9999-110607-B