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, with the LTC3604 track function. Because of the using the LTC3604 monolithic synchronous buck high switching frequency of the LTC3604, which is regulator. The DC1611A has a maximum input volt- programmable up to 4 MHz, the DC1611A uses low age 15V, and is capable of delivering up to 2.5A of profile surface mount components. All these features output current at a minimum input voltage of 3.6V. make the DC1611A an ideal circuit for use in Lith- The output voltage of the DC1611A can be set as low ium-Ion Battery applications and distributed power as 0.6V, the reference voltage of the LTC3604. At systems. Gerber files for this circuit are available. low load currents, the DC1611A operates in discon- Call the LTC Factory. tinuous mode, and during shutdown, it consumes less than 40 uA of quiescent current. In continuous mode Design files for this circuit board are available. Call the operation, the DC1611A is a high efficiency circuit - LTC factory. over 80%. The DC1611A can track another voltage As Shipped Performance Summary PARAMETER CONDITIONS VALUE Minimum Input Voltage 3.6V Maximum Input Voltage 15V GND = Shutdown Run/Shutdown V = Run IN V = 3.6V to 15V, I = 0A to 2.5A 1.2V 4% (1.152V 1.248V) IN OUT Output Voltage V = 3.6V to 15V, I = 0A to 2.5A 1.8V 4% (1.728V 1.872V) IN OUT Regulation V = 4.5V to 15V, I = 0A to 2.5A 3.3V 4% (3.168V 3.432V) IN OUT Typical Output Ripple Voltage V = 12V, V = 1.8V, I = 2.5A (20 MHz BW) < 20mV IN OUT OUT PP Burst Mode V = 12V, V = 1.8V < 700 mA IN OUT Nominal Switching Frequency R = 324k 1 MHz 20% T Table 1. Jumper Description JUMPER FUNCTION RANGE/SETTING (DEFAULT) JP1 Vout Setting. 1.2V JP5 Tracking or Soft-Start (SS) (SS) - TRACK JP6 Mode: Forced Continuous Mode (FCM), Burst Mode, or External Synchronization (SYNC) (FCM) SYNC Burst Mode JP7 Run (ON) - OFF JP8 Frequency (1 MHz) - 2 MHz JP9 ITH: Compensation INT (EXT) 1 L TC3604 QUICK START PROCEDURE Demonstration Circuit 1611 is easy to set up to evalu- output current to any current less than 400 mA. Ob- ate the performance of the LTC3604. For proper serve the discontinuous mode of operation at the measurement equipment configuration, set up the cir- switch node, and measure the output ripple voltage. It cuit according to the diagram in Figure 1. Before pro- should measure less than 150 mV. ceeding to test, insert shunts into the 1.2V position of the output voltage header JP1, into the SS (soft-start) posi- Insert the JP7 shunt into the OFF position and move tion of Track/SS header JP5, into the FCM (Forced Con- the shunt in the 1.2V output JP1 header into any of the tinuous Mode) position of MODE header JP6, into the OFF two remaining output voltage option headers: 1.8V position of RUN header JP7, into the 1 MHz position of (JP2) or 3.3V (JP3). Just as in the 1.2V Vout test, the FREQ header JP8, and into the EXT position of ITH header output voltage should read Vout +/- 2% tolerance un- JP9. der static line and load conditions and +/- 1% toler- ance under dynamic line and load conditions (+/- 2% When measuring the input or output voltage ripple, total). Also, the circuit operation in discontinuous care must be taken to avoid a long ground lead on the mode will be the same. oscilloscope probe. Measure the input or output volt- age ripple by touching the probe tip directly across the When finished, turn off the circuit by inserting the Vin or Vout and GND terminals. See Figure 2 for shunt in header JP7 into the OFF position. proper scope probe measurement technique. Low Output Voltage, 2MHz Operation With the DC1611 set up according to the proper In applications with low output voltages of less than measurement configuration and equipment in Figure 1.2V, and frequencies of 2 MHz or higher, the inductor 1, apply 6.3V at Vin (Do not hot-plug Vin or increase ripple current will be reduced significantly such that the Vin over the rated maximum supply voltage of 15V, or the part may be damaged.). Measure Vout it should internal current comparator will not be able to clearly read 0V. Turn on the circuit by inserting the shunt in differentiate it from surrounding noise. Sporadic ckt. header JP7 into the ON position. The output voltage operation will result. To avoid this effect, replace the should be regulating. Measure Vout - it should meas- standard 1 uH inductor with a 0.47 uH inductor. This ure 1.2V +/- 2% (1.176V to 1.224V). will make the inductor ripple current large enough so that the circuit operation will not be affected. Vary the input voltage from 3.6V to 15V and adjust the load current from 0 to 2.5A. Vout should set the input Warning - If the power for the demo board is carried in voltage to 15V and the output current to 2.5A. Meas- long leads, the input voltage at the part could ring, ure the output ripple voltage it should measure less which could affect the operation of the circuit or even than 20 mVAC. exceed the maximum voltage rating of the IC (which, of course, may damage the IC). To eliminate the ringing, a Observe the voltage waveform at the switch pins (the small tantalum capacitor has been inserted on the pads other side of the inductor from the output). Verify the between the input power and return terminals on the switching frequency is between 800 kHz and 1.2 MHz bottom of the demo board. The (greater) ESR of the (T = 1.25 us and 0.833 us), and that the switch node tantalum capacitor will dampen the (possible) ringing waveform is rectangular in shape. voltage due to the use of long input leads. On a normal, typical PCB, with short traces, the capacitor is not Change the JP6 shunt from forced continuous mode to needed. Burst Mode. Also set the input voltage to 12V and the 2