QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 893 MONOLITHIC BUCK REGULATOR WITH DUAL VLDO REGULATORS LTC3446 DESCRIPTION Demonstration circuit 893A is a triple output con- provide three reasonably quiet outputs. The DC893A verter, using the LTC3446 monolithic synchronous is meant for powering sub-2V logic circuits and I/O buck regulator with dual very low drop-out linear circuitry from a single Li-Ion battery. With the dual regulators (VLDOs). The DC893A has an input volt- VLDOs running off the output voltage of the buck age range of 2.7V to 5.5V, and is capable of delivering regulator, the efficiency of the linear regulators can up to 300 mA of load current on each output. The rival that of the buck regulator. These features make buck regulator output voltage of the DC893A can be the DC893A an ideal circuit for use in Battery pow- set as low as 0.8V, and the dual VLDOs can be set as ered, hand-held applications. low as 0.4V. The DC893A can operate in noise sensi- Design files for this circuit board are available. Call tive applications, due to the LTC3446 buck regulator the LTC factory. operating in pulse-skipping mode at low load cur- LTC is a trademark of Linear Technology Corporation rents. This feature, together with the inherent low noise operation of the VLDOs, allows the DC893A to Table 1. Performance Summary (T = 25C) A PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.7V Maximum Input Voltage 5.5V GND = Shutdown Run/Shutdown V = Run IN Output Voltage V V = 2.7V to 5.5V, I = 0 mA to 400 mA 1.8V ~5% (1.7V 1.9V) OUTBUCK IN OUTBUCK Line 1.5% Output Voltage Regulation V OUTBUCK Load 1.5% Typical Output Ripple V V = 3.3V, I = 400 mA (20 MHz BW) < 40mV OUTBUCK IN OUTBUCK PP Nominal Switching Frequency 2.25 MHz Burst Mode - V = 3.3V, V = 1.8V <0.4A 0.1A% IN OUTBUCK Operation Modes Pulse-Skipping - V = 3.3V, V = 1.8V <0.2A 50 mA% IN OUTBUCK Output Voltage V V = 2.9V to 5.5V, I = 0 mA to 300 mA 1.5V ~5% (1.4V - 1.6V) OUTLDO1 IN OUT1 Line 1.5% Output Voltage Regulation V OUTLDO1 Load 1.5% Typical Output Ripple V V = 3.3V, I = 300 mA (20 MHz BW) < 20mV OUTLDO1 IN OUTLDO1 PP Output Voltage V V = 2.7V to 5.5V, I = 0 mA to 300 mA 1.2V ~5% (1.125V - 1.275V) OUTLDO2 IN OUTLDO2 Line 1.5% Output Voltage Regulation V OUTLDO2 Load 1.5% Typical Output Ripple V V = 3.3V, I = 300 mA (20 MHz BW) < 20mV OUTLDO2 IN OUTLDO2 PP 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 893 MONOLITHIC BUCK REGULATOR WITH DUAL VLDO REGULATORS QUICK START PROCEDURE The DC893 is easy to set up to evaluate the perform- technique) they should measure less than 40 ance of the LTC3446. For a proper measurement mVAC each. Also, observe the voltage wave- equipment configuration, set up the circuit according form of the VoutBuck regulator at the switch to the diagram in Figure 1. node (pin 14). The switching frequency should be between 1.8 MHz and 2.7 MHz (T = NOTE: When measuring the input or output voltage 555 ns and 370s). ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or out- 7. Insert shunts XJP2, XJP3, and XJP4 into the put voltage ripple by touching the probe tip directly OFF position(s). Move shunt XJP1 into the across the Vin or Vout and GND terminals. See the Burst-Mode position. Turn on VoutBuck by probe measurement diagram in Figure 2 for proper moving shunt XJP2 into the on position and scope probe technique. lower the load current to less than 40 mA. Observe the output ripple voltage. It should Please follow the procedure outlined below for proper measure less than 100 mVAC. operation. 8. Measure the output voltage it should meas- 1. Connect the input power supply to the Vin and ure +/- 2.5% tolerance for static line and load GND terminals. Connect the loads between conditions and +/- 6% tolerance under dy- the Vout and GND terminals. Refer to figure 1 namic line and load conditions (3.5% total). for the proper measurement equipment setup. When finished, turn off the VoutBuck circuit 2. Before proceeding to operation, insert shunt by inserting a shunt into the OFF position of XJP1 into the pulse-skip position of jumper JP2, and disconnect the power. JP1. Also, insert shunts XJP2, XJP3, and XJP4 into the OFF positions of jumpers JP2, JP3, and JP4, respectively. 3. Apply 5V at Vin, and turn on VoutBuck, Warning - If the power for the demo board is carried LVout1, and LVout2 by changing shunts XJP2, in long leads, the input voltage at the part could XJP3, and XJP4 from the OFF positions to the ring, which could affect the operation of the circuit ON positions. All three output voltages or even exceed the maximum voltage rating of the IC. should be within a tolerance of +/- 2.5%. To eliminate the ringing, insert a small tantalum ca- pacitor (for instance, AVX part TAJW476M010) on 4. Vary the input voltage from 2.9V to 5V. The the pads between the input power and return termi- three output voltages should be within +/- nals on the bottom of the demo board. The (greater) 3.5% tolerance. ESR of the tantalum will dampen the (possible) ring- 5. Vary the load current, of each output, from 0 ing voltage due to the use of long input leads. On a to full load (400 mA for VoutBuck, 300 mA for normal, typical PCB, with short traces, the capacitor LVout1 and LVout2). Each output voltage is not needed. should be within a tolerance of +/- 5%. 6. Set the load current of all outputs to full load and measure the ripple voltage of each output (refer to Figure 2 for proper measurement 2