MIC22700YML-EV

MIC22700YML Evaluation Board Integrated 7A Synchronous Buck Regulator General Description The Micrel MIC22700 is a high-efficiency, 7A, integrated, synchronous buck (step-down) regulator. The MIC22700 is optimized for highest power density and achieves over 90% efficiency while switching at 1MHz with only 1µH inductor and 100µF output capacitor. The MIC22700 features integrated 7A MOSFETs, flexible sequencing and tracking abilities. This board enables the evaluation of the MIC22700; a high power density, synchronous buck regulator. The board is optimized for ease of testing, with all the components on a single side. The voltage-mode feedback loop is designed to allow high bandwidth with just two external compensation components. The high-side MOSFET is a P-Channel, allowing duty cycle control up to 100%. The ultra-high-speed control loop keeps the output voltage within regulation even under extreme transient load swings commonly found in FPGAs and low voltage ASICs. The output voltage can be adjusted down to 0.7V to address all low voltage power needs. The MIC22700 offers a fullrange of sequencing and tracking options. The enable/delay pin combined with the Power Good/Poweron-Reset (PG/POR) pin allows multiple outputs to be sequenced in any way on turn-on and turn-off. The RC (Ramp Control™) pin allows the device to be connected to another MIC22700 device to keep the output voltages within a certain delta V on start-up. Requirements This board needs a single bench power source adjustable over the input voltage of 2.6V< VIN < 5.5V that can provide at least 7A of current. The loads can either be active (electronic load) or passive (resistor) with the ability to dissipate the maximum load power while keeping accessible surfaces ideally < 70°C. Precautions There is no reverse input protection on this board. When connecting the input sources, ensure that the correct polarity is observed. Under extreme load conditions such as short circuit testing, input transients can be quite large if long test leads are used. In such cases, place a 100µF, 6.3V Tantalum capacitor at the VIN terminals to prevent over voltage damage to the IC. Getting Started 1. Connect VIN supply to the input terminals +VIN and GND. With the output of this supply disabled, set its voltage to the desired input test voltage (2.6V< VIN < 5.5V). This supply voltage should be monitored at the test boards input terminals to allow voltage drops in the test cables (and ammeter if used) to be accounted for. An ammeter can be added inline with the +VIN input terminal to accurately measure input current. 2. Connect the loads to the output terminals between +VO and GND. Again, this output voltage should be monitored by connecting the voltmeter at the +VO and GND terminals. An ammeter can be added inline with the +VO terminal of the evaluation board to accurately measure the output current. Output voltage is set to 1.8V. Output voltage can be changed by selecting the resistor R2. The resistor divider network for a desired VOUT is given by: R2 = R1 ⎛ VOUT ⎜ ⎜V ⎝ REF ⎞ ⎟ ⎟ ⎠ −1 where VREF is 0.7V and VOUT is the desired output voltage. Initially, set the output load to 0A to check that the output is regulating properly prior to loaded tests. 3. Enable the input supply. By default, the output voltage is enabled when an input supply of > 2.5V is applied. When this threshold is crossed, the enable pin capacitor (1nF) begins to charge at 1V/µs until it reaches 1.25V, where switching begins. To test the enable functions of the MIC22700, a test point is provided. Ordering Information Part Number Description MIC22700YML EV Evaluation board with the integrated 7A MIC22700 device Ramp 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 • http://www.micrel.com June 2011 M9999-062411-A Micrel, Inc. MIC22700YML Evaluation Board Other Features Power-on-Reset (POR) Delay Time Input Adding an external capacitor to this Delay pin allows the Power Good delay to be adjusted to perform as a Poweron-Reset (POR). As with the RC pin, this pin has an internal 1µA current source and sink. When VFB reaches 90% of its nominal voltage (~630mV) the internal 1µA current source charges the capacitor on this pin (C8) to the rising threshold of 1.25V, at this point, PG is asserted high. When the enable pin is set low, POR is asserted low immediately. However, the internal ‘Delay’ current sink discharges the capacitor (C8) to 1.25V lower than its starting point, at which point, it enables the RC pin 1µA current sink to begin discharging capacitor C7. Enable Delay Input C6 creates a delay set by an internal 1µA source charging to a 1.25V threshold. A switch (Q1) is used from EN pin to ground as shutdown ‘SHDN’ control. The part will exhibit approximately 1.3µs enable delay from ‘SHDN’ going low to the start of switching. Using a pulse generator with a low impedance output connected to the EN terminal will remove this delay as it defeats the internal 1µA source. RC (Ramp Control™) Capacitor The MIC22700 has a nominal 1µA current source/sink to the RC pin. The startup output voltage waveform tracks the voltage on RC. 100% output voltage is represented by 0.7V on RC. The default capacitor on RC (C7) of 10nF sets the ramp up time to approximately 700µs. Power-on-Reset (POR) Output This is an open drain connection with an on board pull-up resistor (R3) to SVIN. This is only asserted high when the FB pin reaches >90% of its nominal set voltage. This can be used as part of the tracking and sequencing function described in the data sheet. Feedback resistors The output is set nominally at 1.8V. This can be changed by adjusting the upper or lower resistor in the FB potential dividers. It is recommended that R1 or R2 value should be kept