DEMO CIRCUIT 1574A LTC3612 QUICK START GUIDE LTC3612 3A, 4MHz, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR DESCRIPTION Demo Circuit 1574 is a high efficiency, high frequency step-down converter, incorporating the LTC3612 monolithic synchronous regulator. The DC1574A has an input voltage range of 2.25V to 5.5V, and is capable of delivering up to 3A of output current. The output voltage of the DC1574A can be set as low as 0.6V, the reference voltage of the LTC3612. The operating frequency range of the DC1574A is either set to a fixed 2.25 MHz by connecting the frequency pin to SVin, set by an external resistor, or synchronized to an external clock, with a range up to 4 MHz. At low load currents, the DC1574A can operate in either noise sensitive applications, due to the capability of the LTC3612 to operate in pulse-skipping mode, or in high efficiency applications, because the LTC3612 also has Burst-Mode capability. The Burst Mode clamp can be set externally. Of course, in (forced) continuous mode, or large load current applications, the DC1574A is a very efficient circuit - over 90%. The DC1574A consumes less than 200 uA of quiescent current during sleep operation, and during shutdown, it consumes less than 1 uA. The DC1574A can track another voltage, due to the LTC3612 track function, for easy power supply sequencing. Extra features include frequency and current foldback, and an adjustable 0.3V-to-0.6V external reference. Because of the high switching frequency of the LTC3612, which is programmable up to 4 MHz, the DC1574A uses low profile surface mount components. All these features make the DC1574A perfectly suited for portable computer and distributed power applications. Design files for this circuit board are available. Call the LTC factory. As Shipped Performance Summary PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.25V Maximum Input Voltage 5.5V GND = Shutdown Run/Shutdown VIN = 2.25V to 5.5V, IOUT = 0A to 3A VIN = Run 1.2V ±4% (1.152V – 1.248V) VIN = 2.25V to 5.5V, IOUT = 0A to 3A 1.8V ±4% (1.728V – 1.872V) VIN = 3.1V to 5.5V, IOUT = 0A to 3A 2.5V ±4% (2.4V – 2.6V) VIN = 3.9V to 5.5V, IOUT = 0A to 3A 3.3V ±4% (3.168V – 3.432V) Typical Output Ripple Voltage VIN = 5V, VOUT = 1.8V, IOUT = 3A (20 MHz BW) <30mVP–P Burst Mode VIN = 5V, VOUT = 1.8V <600 mA Pulse-Skip Mode VIN = 5V, VOUT = 1.8V <500 mA Nominal Switching Frequency RT = 165k 2 MHz ± 20% Output Voltage Regulation 1 LTC3612 Table 1. Jumper Description JUMPER FUNCTION JP1 Output Voltage Setting. J1 Mode: Forced Continuous Mode (FCM), Burst Mode (BM or BMEC), or Pulse-Skip Mode(SYNC) J2 Run J3 Tracking (TRACK), Internal Soft-Start (INT SS), or External Soft-Start (EXT SS) J4 DDR Memory Termination J5 External or Internal ITH Compensation J6 Frequency Setting: Timing Resistor (RT), Internally Synchronized (INT SYNC - 2.25 MHz), or Externally Synchronized (EXT SYNC) J9 External Burst Mode Clamp Voltage RANGE/SETTING (DEFAULT) 1.2V (FCM) – BMEC – BM - PSM (ON) - OFF (EXT SS) – INT SS - TRACK (OFF) - ON (EXT) – INT (Rt) – INT SYNC – EXT SYNC (SET) – EXT QUICK START PROCEDURE Demonstration Circuit 1574 is easy to set up to evaluate the performance of the LTC3612. 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 FCM (Forced Continuous Mode) position of MODE header J1, into the OFF position of RUN header J2, into the EXT SS (external softstart) position of Track/SS header J3, into the OFF position of DDR header J4, into the EXT (external) position of COMP header J5, into the Rt position of Rt/SYNC header J6, and into the SET position of VBMCV header J9. 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. With the DC1574 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 5.5V, or the part may be damaged.). Measure Vout; it should read 0V. Turn on the circuit by inserting the shunt in header J2 into the ON position. The output voltage should be regulating. Measure Vout - it should measure 1.2V +/- 2% (1.176V to 1.224V). 2 Vary the input voltage from 2.25V to 5.5V and adjust the load current from 0 to 3A. Vout should regulate around 1.2V. Measure the output ripple voltage; it should measure less than 30 mVAC. Observe the voltage waveform at the switch pins (the other side of the inductor from the output). Verify the switching frequency is between 1.6 MHz and 2.4 MHz (T = 625 ns and 416 ns), and that the switch node waveform is rectangular in shape. Change the J1 shunt from forced continuous mode to Burst Mode or pulse-skip mode. Set the input voltage to 5V and the output current to any current less than 600 mA. Observe the discontinuous mode of operation at the switch node, and measure the output ripple voltage. It should measure less than 100 mV. Insert the J2 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), 2.5V (JP3), or 3.3V (JP4). 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 J2 into the OFF position. LTC3612 Figure 1. Proper Measurement Equipment Set-Up Figure 2. Measuring Input or Output Ripple 3 LTC3612 Normal Switching Frequency & Output Ripple Voltage Waveforms Figure 3. Switch Node & Output Ripple Voltage Waveforms VIN = 3.3V, VOUT = 1.8V, IOUT = 3A, FSW = 2 MHz Trace 3: Output Ripple Voltage (20 mV/div AC) Trace 1: Switch Voltage (2 V/div) 4 LTC3612 Load Step Response Waveform Figure 4. Load Step Response VIN = 3.3V, VOUT = 1.8V, 2.5A Load Step (0.5A <-> 3A) Forced Continuous Mode FSW = 2 MHz Trace 3: Output Voltage (100mV/div AC) Trace 4: Output Current (2A/div) 5 LTC3612 6