QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 427B RMS TO DC CONVERTER LTC1966/LTC1967/LTC1968 DESCRIPTION Demonstration circuit 427B features the LTC1966/7/8 Pre- and lower power than conventional log-antilog RMS-to-DC cision Micro-power true RMS-to-DC converter. It incorpo- converters. The LTC1966/7/8 accepts single-ended or dif- rates a variety of passive components to support configu- ferential inputs with rail-to-rail common-mode range. One rations for varied applications. Two optional post-filters standout feature of the LTC1966/7/8 is its superior linear- are included to improve averaging ripple and step re- ity, which allows hassle-free system calibration at any in- sponse performance, as illustrated in the Design Cook- put voltage. book section of the datasheet. DC427B-A contains the Design files for this circuit board are available. Call LTC1966, DC427B-B contains the LTC1967, and DC427B- the LTC factory. C contains the LTC1968. , LTC and LT are registered trademarks of Linear Technology Corporation. The LTC1966/7/8 is a patent-pending DS-based RMS to DC converter that is simpler, more accurate, more flexible, QUICK START PROCEDURE Table 1 shows the Jumper positions and their respective Table 1: DC427B Jumpers (default positions in bold) effects. Be sure that the jumpers are in the bold (default) JUMPER SETTING EFFECT positions. Refer to Figure 1 for the connection diagram JP1 Top LTC1966/7/8 shutdown and follow the procedure below: Bottom LTC1966/7/8 always enabled 1. Connect the power supplies as shown. The power labels Removed LTC1966/7/8 controlled by E2 input of V and V directly correspond to pins 4 and 7 of the SS DD to DC427 LTC1966/7/8, respectively, and combinations other than JP2 Left IN1 grounded 5V may be used. The LTC1966 accepts dual 5V sup- Right IN1 active (J1 connected to pin 2) plies, and the LTC1967/8 accept single 5V supplies re- fer to the respective datasheet and the Supply Voltages JP3 Top Vout (pin 5) connected to optional DC-Accurate post-filter section of this Quick Start Guide. Right Vout connected to output terminal 2. Apply an input signal to convert from RMS to DC to E4, no filter IN1. Any signal generator may be used the LTC1966 Bottom Vout connected to optional buffered works up to 1V with V = 5V. PEAK DD post-filter NOTE: There is a 50W termination to ground on DC427B JP4 Left IN2 grounded remove if driving IN1 or IN2 with an op-amp. Right IN2 active (J2 connected to pin 3) 3. Observe the output with a digital voltmeter (DVM) con- JP5 Top OutRtn (pin 6) grounded nected to terminals E4 and E7. Bottom OutRtn connected to VSS NOTE: The LTC1966/7/8 output impedance is high, and Removed OutRtn floating drive with voltage at 10MW DVM input impedance will cause up to terminal E7 1% gain error. JP6 Left LTC1966/7/8 negative supply (Pin 1) connected to VSS 4. To use the optional output filters, reposition JP3 and observe the output at terminal E1 or E8. Right Pin 1 grounded 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 427B RMS TO DC CONVERTER Note: LTC1967 and LTC1968 run on single 5V supplies. See Supply Voltages section (below) and product datasheet. Figure 1. Proper Measurement Equipment Setup ADDITIONAL FEATURES Although the 427B demo board is ready to use out of the has a footprint that will accommodate 2.5mm, 5mm, box (See Quick Start Procedure above), it has features 7.5mm, and 10mm spaced through-hole leaded compo- that you can access by adding, removing or changing nents as well as a large solder mask-free area for use with components on the board. Here are some ways that you a wide variety of surface mount case sizes. Try out the can change the configuration to take advantage of these averaging capacitor you intend to use with the features. LTC1966/7/8 in 427B. DIFFERENTIAL INPUTS SUPPLY VOLTAGES To drive the input differentially, move jumper JP4 from left The LTC1967/8 are single 5V supply converters. V and DD to right. The LTC1966/7/8 will respond to the difference of V on the DC427B connect to Pin 7 and Pin 4 of the IC, SS the signals. If two different frequencies are used, the vec- but the supply pins of the LTC1967/8 are Pin 7 and Pin 1 tor sum results. (Pin 4 is NC). On the DC427B-B and DC427B-C, use JP6 to select whether the negative supply voltage of the AVERAGING CAPACITORS LTC1967/8 will be VSS or ground. The board provides space for trying out different averaging (and filtering) capacitors. The space at C7B parallels C7A (the included metal film averaging capacitor). The space 2