IRDC3898-Vtt rail TM SupIRBuck USER GUIDE FOR Vtt RAIL EVALUATION BOARD USING IR3898 DESCRIPTION Pulse by pulse current limit and output over- The IR3898 is a synchronous buck current protection function is implemented by converter, providing a compact, high sensing the voltage developed across the on- performance and flexible solution in a small resistance of the synchronous rectifier 4mm X 5 mm Power QFN package. MOSFET for optimum cost and performance and the current limit is thermally compensated. Key features offered by the IR3898 include internal Digital Soft Start/Soft Stop, precision This user guide contains the schematic and bill 0.5Vreference voltage, Power Good, of materials for the IR3898 evaluation board. thermal protection, programmable switching The guide describes operation and use of the frequency, Enable input, input under-voltage evaluation board itself. Detailed application lockout for proper start-up, enhanced line/ information for IR3898 is available in the load regulation with feed forward, external IR3898 data sheet. frequency synchronization with smooth clocking, internal LDO and pre-bias start- up. BOARD FEATURES V = +1.5V (1.35Vminimum) in V = +0.75V 0- 4.3A (+0.675V 0-4.3A) out F =600KHz s L= 1.0uH C = 3x22uF (ceramic 805) in C =4x22uF (Ceramic 0805) out 3/17/2011 Confidential 1 This evaluation board is a preliminary version meant for the engineering evaluation of the IR3898. Based on the results of the continuing evaluation, this board can evolve and change without noticeIRDC3898-Vtt rail CONNECTIONS and OPERATING INSTRUCTIONS A well regulated +1.5V input supply should be connected to VIN+ and VIN-. A maximum of 4.3A load should be connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I. IR3898 has an internal LDO which generates Vcc from Vin. To use internal LDO, 12V input should be connected between Vin pin and PGnd. (Vin can be applied across C32 capacitor.) If operation with external Vcc is required, then external Vcc can be applied between Vcc+ and Vcc- pins. Vin pin and Vcc/LDOout pins should be shorted together for external Vcc operation. External Enable signal must be applied to the board between Enable and Agnd pins. Table I. Connections Connection Signal Name VIN+ Vin (+12V) VIN- Ground of Vin Vout+ Vout(+1V0) Vout- Ground for Vout Vcc+ Vcc/ LDO out Pin Vcc- Ground for Vcc input Enable Enable P Good Power Good Signal AGnd Analog ground LAYOUT The PCB is a 4-layer board. All layers use 2 Oz. copper. The IR3898 and other major power components are mounted on the top side of the board. Power supply decoupling capacitors, the bootstrap capacitor and feedback components are located close to IR3898. To improve efficiency, the circuit board is designed to minimize the length of the on- board power ground current path. 3/17/2011 Confidential 2 This evaluation board is a preliminary version meant for the engineering evaluation of the IR3898. Based on the results of the continuing evaluation, this board can evolve and change without notice