DEMO CIRCUIT 1611A LTC3604 QUICK START GUIDE LTC3604EMSE 2.5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR DESCRIPTION Demonstration circuit 1611 is a step-down converter, using the LTC3604 monolithic synchronous buck regulator. The DC1611A has a maximum input voltage 15V, and is capable of delivering up to 2.5A of output current at a minimum input voltage of 3.6V. The output voltage of the DC1611A can be set as low as 0.6V, the reference voltage of the LTC3604. At low load currents, the DC1611A operates in discontinuous mode, and during shutdown, it consumes less than 40 uA of quiescent current. In continuous mode operation, the DC1611A is a high efficiency circuit over 80%. The DC1611A can track another voltage with the LTC3604 track function. Because of the high switching frequency of the LTC3604, which is programmable up to 4 MHz, the DC1611A uses low profile surface mount components. All these features make the DC1611A an ideal circuit for use in Lithium-Ion Battery applications and distributed power systems. Gerber files for this circuit are available. Call the LTC Factory. Design files for this circuit board are available. Call the LTC factory. As Shipped Performance Summary PARAMETER CONDITIONS VALUE Minimum Input Voltage 3.6V Maximum Input Voltage 15V GND = Shutdown Run/Shutdown VIN = 3.6V to 15V, IOUT = 0A to 2.5A VIN = Run 1.2V ±4% (1.152V – 1.248V) VIN = 3.6V to 15V, IOUT = 0A to 2.5A 1.8V ±4% (1.728V – 1.872V) VIN = 4.5V to 15V, IOUT = 0A to 2.5A 3.3V ±4% (3.168V – 3.432V) Typical Output Ripple Voltage VIN = 12V, VOUT = 1.8V, IOUT = 2.5A (20 MHz BW) < 20mVP–P Burst Mode VIN = 12V, VOUT = 1.8V < 700 mA Nominal Switching Frequency RT = 324k 1 MHz ± 20% Output Voltage Regulation Table 1. Jumper Description JUMPER JP1 JP5 JP6 JP7 JP8 JP9 FUNCTION Vout Setting. Tracking or Soft-Start (SS) Mode: Forced Continuous Mode (FCM), Burst Mode, or External Synchronization (SYNC) Run Frequency ITH: Compensation RANGE/SETTING (DEFAULT) 1.2V (SS) - TRACK (FCM) – SYNC – Burst Mode (ON) - OFF (1 MHz) - 2 MHz INT – (EXT) 1 LTC3604 QUICK START PROCEDURE Demonstration Circuit 1611 is easy to set up to evaluate the performance of the LTC3604. For proper measurement equipment configuration, set up the circuit according to the diagram in Figure 1. Before proceeding to test, insert shunts into the 1.2V position of the output voltage header JP1, into the SS (soft-start) position of Track/SS header JP5, into the FCM (Forced Continuous Mode) position of MODE header JP6, into the OFF position of RUN header JP7, into the 1 MHz position of FREQ header JP8, and into the EXT position of ITH header JP9. When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe measurement technique. output current to any current less than 400 mA. Observe the discontinuous mode of operation at the switch node, and measure the output ripple voltage. It should measure less than 150 mV. Insert the JP7 shunt into the OFF position and move the shunt in the 1.2V output JP1 header into any of the two remaining output voltage option headers: 1.8V (JP2) or 3.3V (JP3). Just as in the 1.2V Vout test, the output voltage should read Vout +/- 2% tolerance under static line and load conditions and +/- 1% tolerance under dynamic line and load conditions (+/- 2% total). Also, the circuit operation in discontinuous mode will be the same. When finished, turn off the circuit by inserting the shunt in header JP7 into the OFF position. Low Output Voltage, 2MHz Operation With the DC1611 set up according to the proper measurement configuration and equipment in Figure 1, apply 6.3V at Vin (Do not hot-plug Vin or increase Vin over the rated maximum supply voltage of 15V, or the part may be damaged.). Measure Vout; it should read 0V. Turn on the circuit by inserting the shunt in header JP7 into the ON position. The output voltage should be regulating. Measure Vout - it should measure 1.2V +/- 2% (1.176V to 1.224V). Vary the input voltage from 3.6V to 15V and adjust the load current from 0 to 2.5A. Vout should set the input voltage to 15V and the output current to 2.5A. Measure the output ripple voltage; it should measure less than 20 mVAC. Observe the voltage waveform at the switch pins (the other side of the inductor from the output). Verify the switching frequency is between 800 kHz and 1.2 MHz (T = 1.25 us and 0.833 us), and that the switch node waveform is rectangular in shape. Change the JP6 shunt from forced continuous mode to Burst Mode. Also set the input voltage to 12V and the 2 In applications with low output voltages of less than 1.2V, and frequencies of 2 MHz or higher, the inductor ripple current will be reduced significantly such that the internal current comparator will not be able to clearly differentiate it from surrounding noise. Sporadic ckt. operation will result. To avoid this effect, replace the standard 1 uH inductor with a 0.47 uH inductor. This will make the inductor ripple current large enough so that the circuit operation will not be affected. Warning - If the power for the demo board is carried in long leads, the input voltage at the part could “ring”, which could affect the operation of the circuit or even exceed the maximum voltage rating of the IC (which, of course, may damage the IC). To eliminate the ringing, a small tantalum capacitor has been inserted on the pads between the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum capacitor will dampen the (possible) ringing voltage due to the use of long input leads. On a normal, typical PCB, with short traces, the capacitor is not needed. LTC3604 Figure 1. Proper Equipment Measurement Set-Up Figure 2. Measuring Input or Output Ripple 3 LTC3604 Normal Switching Frequency & Output Ripple Voltage Waveforms Figure 3. Switch Node & Output Ripple Voltage Waveforms VIN = 12V, VOUT = 1.8V, IOUT = 2.5A, FSW = 2 MHz Trace 3: Output Ripple Voltage (20 mV/div AC) Trace 2: Switch Voltage (10 V/div) 4 LTC3604 Load Step Response Waveform Figure 4. Load Step Response VIN = 12V, VOUT = 1.8V, 2.5A Load Step (0A <-> 2.5A) Forced Continuous Mode FSW = 2 MHz Trace 3: Output Voltage (50mV/div AC) Trace 4: Output Current (1A/div) 5 LTC3604 6