USERS MANUAL ISL8105AEVAL1Z AN1258 Rev 0.00 Evaluation Board Nov 1, 2007 Description The ISL8105AEVAL1Z evaluation board highlights the V = 12V, V = 1.8V, I = 10A IN OUT OUT operations of the ISL8105A controller in a DC/DC application. The evaluation board is configured for an output voltage of V OUT 1.8V and 15A maximum load. COMP-EN FIGURE 2. SOFT-START Figure 1 shows the start-up profile of the ISL8105AEVAL1Z in relation to the start-up of the 12V input supply and the bias FIGURE 1. ISL8105AEVAL1Z EVALUATION BOARD supply. Power and Load Connections Soft-Start with Pre-Biased Output INPUT VOLTAGE If the output is pre-biased to a voltage less than the expected The evaluation board is optimized for an input supply of 12V, value, the ISL8105A will detect that condition. Neither however, the input supply based on the connection can MOSFET will turn on until the soft-start ramp voltage range from 4.5V to 5.5V or 6.5V to 14.4V. exceeds the output V starts seamlessly ramping from OUT there. The IC bias supply and the converter input voltage are connected together through R to provide single rail power 10 V = 12V, V = 1.8V, I = 1A IN OUT OUT supply application. OUTPUT VOLTAGE LOADING AND MONITORING V OUT Connect the positive lead of the electronic load and the positive lead of a digital multimeter to the V terminal (J4) OUT COMP-EN and the ground lead to the GND terminal (J5). The scope probe terminal (TPV01) can be used to monitor V with OUT an oscilloscope. Start-up The ISL8105A starts up when V rises above POR BIAS threshold and the COMP/EN rises above V level. The DISABLE FIGURE 3. SOFT-START WITH PRE-BIASED OUTPUT entire start-up time sequence from POR typically takes up to 17ms. There is fixed 6.8ms delay for the POR to initiate the Overcurrent Protection (OCP) sample and hold operation. The OCP sample and hold operation takes an additional 0ms to 3.4ms (the longer time occurs with the higher overcurrent setting). When the OCP sampling and hold operations are done, the soft-start function internally ramps the reference on the non-inverting terminal of the error amp from 0V to 0.6V in 6.8ms (typ). AN1258 Rev 0.00 Page 1 of 8 Nov 1, 2007ISL8105AEVAL1Z Output Performance V OUT Switching Frequency The evaluation board comes with a ISL8105A that has a fixed switching frequency of 600kHz. I OUT Output Ripple Figure 4 shows the ripple voltage on the output of the regulator. V OUT FIGURE 6. TRANSIENT RESPONSE V OUT I FIGURE 4. OUTPUT VOLTAGE RIPPLE (20MHz BW) OUT V OUT FIGURE 7. TRANSIENT RESPONSE V OUT FIGURE 5. OUTPUT VOLTAGE RIPPLE AND NOISE (500MHz BW) I OUT Transient Performance Figures 6, 7 and 8 show the response of the output when subjected to transient loading from 7.5A to 15A. Overcurrent Protection The overcurrent function limits the output current by using the bottom-side MOSFETs r to monitor the current. A DS(ON) FIGURE 8. TRANSIENT RESPONSE resistor, R , (R ) programs the overcurrent trip level. This BSOC 8 method enhances the converter s efficiency and reduces cost by eliminating a current sensing resistor. If overcurrent is detected, the output immediately shuts off, it cycles the soft-start function in a hiccup mode (2 dummy soft-start time-outs, then up to one real one) to provide fault protection. If the shorted condition is not removed, this cycle will continue indefinitely. Figure 9 shows the overcurrent response and hiccup mode operation. AN1258 Rev 0.00 Page 2 of 8 Nov 1, 2007