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ISO120 Datasheet(PDF) 8 Page - Burr-Brown (TI) |
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ISO120 Datasheet(HTML) 8 Page - Burr-Brown (TI) |
8 / 16 page 8 ISO120/121 BASIC OPERATION Signal and Power Connections Figure 3 shows proper power and signal connections. Each power supply pin should be bypassed with 1 µF tantalum capacitor located as close to the amplifier as possible. All ground connections should be run independently to a com- mon point if possible. Signal Common on both input and output sections provide a high-impedance point for sensing signal ground in noisy applications. Signal Common must have a path to ground for bias current return and should be maintained within ±1V of Gnd. The output sense pin may be EXTERNAL CLOCK FREQUENCY RANGE C X 400kHz to 700kHz 30pF 200kHz to 400kHz 180pF 100kHz to 200kHz 680pF 50kHz to 100kHz 1800pF 20kHz to 50kHz 3300pF 10kHz to 20kHz 0.01 µF 5kHz to 10kHz 0.022 µF 10k Ω C X OPA602 R X 1µF Sq Wave In Triangle Out to ISO120/121 Ext Osc 1k Ω FIGURE 2. Square Wave to Triangle Wave Signal Condi- tioner for Driving ISO120/121 Ext Osc Pin. TABLE II. Recommended C X Values vs Frequency for Figure 2 Circuit. C 1 (1) C 1H C 1L –V S1 – +V S1 + +1µF +1µF + +V S1 Signal Com1 Gnd1 V IN Guard Ext (2) Osc C 2 (1) C 2H C 2L –V S2 – +V S2 + +1µF Guard 1µF + +VS2 Gnd 2 Signal Com 2 R L V OUT Sense Isolation Barrier NOTE: (1) Optional. See text. (2) Ground if not used. FIGURE 3. Power and Signal Connections. connected directly to V OUT or may be connected to a remote load to eliminate errors due to IR drops. Pins are provided for use of external integrator capacitors. The C 1H and C2H pins are connected to the integrator summing junctions and are therefore particularly sensitive to external pickup. This sensitivity will most often appear as degraded IMR or PSR performance. AC or DC currents coupled into these pins results in V ERROR = IERROR X 200kΩ at the output. Guarding of these pins to their respective Signal Common, or C 1L and C 2L is strongly recommended. For similar reasons, long traces or physically large capacitors are not desirable. If wound-foil capacitors are used, the outside foil should be connected to C 1L and C2L, respectively. Optional Gain and Offset Adjustments Rated gain accuracy and offset performance can be achieved with no external adjustments, but the circuit of Figure 4a may be used to provide a gain trim of ±0.5% for values shown; greater range may be provided by increasing the size of R 1 and R 2. Every 2k Ω increase in R 1 will give an additional 1% adjustment range, with R 2 ≥ 2R1. If safety or convenience dictates location of the adjustment potenti- ometer on the other side of the barrier from the position shown in Figure 4a, the positions of R 1 and R2 may be reversed. Gains greater than one may be obtained by using the circuit of Figure 4b. Note that the effect of input offset errors will be multiplied at the output in proportion to the increase in gain. Also, the small-signal bandwidth will be decreased in inverse proportion to the increase in gain. In most instances, a precision gain block at the input of the isolation amplifier will provide better overall performance. Figure 5 shows a method for trimming V OS of the ISO120 and ISO121. This circuit may be applied to either Signal Com (input or output) as desired for safety or convenience. With the values shown, ±15V supplies and unity gain, the circuit will provide ±150mV adjustment range and 0.25mV |
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Similar Description - ISO120 |
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