USERS MANUAL ISL85033-12VEVAL3Z AN1636 Rev 1.00 Wide VIN Negative VOUT Buck-Boost Regulator With Up to 5A Output Current July 27, 2011 Evaluating the Other Output Voltages Hardware Description The ISL85033-12VEVAL3Z kit output is preset to -12V The ISL85033 is a wide input range, dual standard buck however, output voltages can be adjusted from -3.3V to -15V. converter that can be configured to provide a negative output The output voltage programming resistor, R3, depends on the voltage. The ISL85033-12VEVAL3Z evaluation board is used in desired output voltage of the regulator. The value for the this application note to demonstrate the negative feedback resistor is typically between 0 and 142k as configuration. In this configuration, V can range from 4.5V to IN shown in Equation 1. (28V - V ). OUT VOUT The ISL85033 is offered in a 4mmx4mm 28 Ld TQFN package R3 = R2 -------------- 1 (EQ. 1) VFB with 1mm maximum height. The complete converter occupies 2 6.25cm area. Table 1 summarizes the external component selection for V = -5V, V = -12V, and V = -15V. OUT OUT OUT Key Features TABLE 1. COMPONENT SELECTION FOR V OUT Wide Input Voltage Range from 4.5V to (28V - V ) OUT V EXTERNAL COMPONENTS OUT Adjustable and Synchronizable Negative Output Voltage with Continuous Output Current up to 5A, depending on V and -5V R3 = 43.2k R5 = 20k C4 = 2.7nF OUT C20 = 22F (1210 ceramic) V IN C17 = 22F (1210 ceramic) Current Mode Control C19 = 68F (15m polymer EEFUD0K680R) Adjustable Switching Frequency from 300kHz to 2MHz -12V R3 = 112k R5 = 120k C4 = 4.7nF Power-Good Detection (referenced to V ) C14, C17 = 22F (2210 ceramic) OUT C12, C19 = 68F (70m TaNbO2 TPSD686M020R0070) Externally Adjustable Soft-start Time C20 = DNP Overcurrent and Hiccup Mode Short Circuit Protection, -15V R3 = 142k R5 = 120k C4 = 4.7nF Thermal Overload Protection, UVLO C14, C17 = 22F (2210 ceramic) Boot Undervoltage Detection C12, C19 = 68F (70m TaNbO2 TPSD686M020R0070) C20 = DNP Default Out-of-phase Channels Reduce Voltage Ripple and Component Size. User-selectable Phase Operation. The curves in Figure 1 indicate the maximum output current the converter can deliver as a function of the input voltage and Recommended Equipment the selected output voltage configuration. The following materials are recommended to perform testing: Figures 2, 3 and 4 show the efficiency for different V , V IN OUT 0V to 30V power supply with at least 7A source current and load combinations. capability or a 5V battery Electronic loads capable of sinking current up to 7A Digital multimeters (DMMs) 100MHz quad-trace oscilloscope Signal generator Quick Setup Guide 1. Ensure that the circuit is correctly connected to the supply and loads prior to applying any power. 2. Connect the bias supply to VIN1, the plus terminal to VIN1, and the negative return to GND1. 3. Verify that the position is ON for S1. 4. Turn on the power supply. 5. Verify the output voltage is -12V for V . OUT AN1636 Rev 1.00 Page 1 of 7 July 27, 2011ISL85033-12VEVAL3Z 6 95 V = 12V IN 90 5 V = -5V OUT 85 V = 5V IN 4 80 3 V = -12V OUT 75 2 V = -15V OUT 70 1 65 0 60 5 7 9 11 13 15 17 19 21 23 25 0 0.5 1.0 1.5 2.0 2.5 I (A) V (V) OUT IN FIGURE 1. ISL85033-12VEVAL3Z BUCK BOOST: RECOMMENDED FIGURE 2. ISL85033-12VEVAL3Z EFFICIENCY: V = -15V OUT MAXIMUM I (V ) OUT IN 95 95 V = 6V V = 12V IN IN V = 15V V = 12V IN IN 90 90 85 85 V = 5V IN V = 5V IN 80 80 V = 15V IN 75 75 70 70 65 65 60 60 0 0.5 1.0 1.5 2.0 2.5 0 0.5 1.0 1.5 2.0 2.5 I (A) I (A) OUT OUT FIGURE 3. ISL85033-12VEVAL3Z EFFICIENCY: V = -12V FIGURE 4. ISL85033-12VEVAL3Z EFFICIENCY: V = -5V OUT OUT If the output voltage desired is -0.8V, then R3 is shorted. The Disabling/Enabling Function value for R2 is typically between 1k and 10k. Note that if The ISL85033-12VEVAL3Z evaluation board contains an S1 V < 2.5V (i.e., -0.8V), the switching frequency and OUT switch that enables or disables both channels, thus allowing a compensation must be changed to accommodate the 300kHz low quiescent current state. Table 2 details this function. operation, due to minimum on-time limitation. Please refer to the ISL85033 data sheet for further information. TABLE 2. SWITCH SETTINGS S1 ON/OFF CONTROL Frequency Control ON Enable V The ISL85033-12VEVAL3Z evaluation board has an FS pin that OUT controls the frequency of operation. Programmable frequency OFF Disable V OUT allows for optimization between efficiency and external component size. Default switching frequency is 500kHz when FS NOTE: If driven externally, the EN signal (the same as all input is tied to VCC (R9 = 0). By removing R9 and connecting R10 to logic signals) is referenced to V (the most negative potential OUT the most negative potential on the board (V ), the switching OUT on the board) and not to GND. Therefore, the source cannot be frequency could be changed from 300kHz (R10 = 383k) to 2MHz GND referenced, and input level shifting is required. (R10 = 40.2k). See the ISL85033 data sheet for information about calculating the value of R10. Do not leave this pin floating. AN1636 Rev 1.00 Page 2 of 7 July 27, 2011 EFFICIENCY (%) I (A) OUT EFFICIENCY (%) EFFICIENCY (%)