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MPC100 Datasheet(PDF) 9 Page - Burr-Brown (TI) |
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MPC100 Datasheet(HTML) 9 Page - Burr-Brown (TI) |
9 / 15 page 9 ® MPC100 APPLICATIONS INFORMATION The MPC100 operates from ±5V power supplies (±6V maximum). Do not attempt to operate with larger power supply voltages or permanent damage may occur. The buffer outputs are not current-limited or protected. If the output is shorted to ground, currents up to 18mA could flow. Momen- tary shorts to ground (a few seconds) should be avoided, but are unlikely to cause permanent damage. INPUT PROTECTION All pins on the MPC100 are internally protected from ESD by means of a pair of back-to-back reverse-biased diodes to either power supply as shown in Figure 1. These diodes will begin to conduct when the input voltage exceeds either power supply by about 0.7V. This situation can occur with loss of the amplifier’s power supplies while a signal source is still present. The diodes can typically withstand a continu- ous current of 30mA without destruction. To insure long term reliability, however, diode current should be externally limited to 10mA or less whenever possible. The internal protection diodes are designed to withstand 2.5kV (using Human Body Model) and will provide ad- equate ESD protection for most normal handling proce- dures. However, static damage can cause subtle changes in amplifier input characteristics without necessarily destroy- ing the device. In precision buffer amplifiers, this may cause a noticeable degradation of offset voltage and drift. There- fore, static protection is strongly recommended when han- dling the MPC100. Static damage has been well recognized for MOSFET de- vices, but any semiconductor device deserves protection from this potentially damaging source. The MPC100 incor- porates on-chip ESD protection diodes as shown in Figure 1. This eliminates the need for the user to add external protec- tion diodes, performance. DISCUSSION OF PERFORMANCE The MPC100 video multiplexer allows the user to connect any one of four analog input channels (IN1-IN4) to the output of the component and to switch between channels within less than 0.5 µs. It consists of four identical unity-gain buffer amplifiers, which are connected together internally at the output. The open loop buffers consisting of complementary –V CC +V CC ESD Protection diodes internally connected to all pins. Internal Circuitry External Pin FIGURE 1. Internal ESD Protection. emitter followers applies no feedback, so their low fre- quency gain is slightly less than unity and somewhat depen- dent on loading. Unlike devices using MOS bilateral switch- ing elements, the bipolar complementary buffers form an unidirectional transmission path and thus provide high out- put-to-input isolation. Switching stages compatible to TTL level digital signals are provided for each buffer to select the input channel. When no channel is selected, the output of the device is high-impedance and allows the user to wire more MPC100s together to form switch multi-channel matrices. If one channel is selected with a digital “1” at the corre- sponding SEL-input, the MPC100 acts as a buffer amplifier with high input impedance and low output impedance. The truth table on the front page describes the relationship between the digital inputs (SEL1 to SEL4) and the analog inputs (IN1 to IN4), and which signal is selected at the output. The 2-4 address decoder and chip select logic is not integrated. The selected design increases the flexibility of address decoding in complex distribution fields, eases BUS-controlled channel selection, simplifies channel se- lection monitoring for the user, and lowers transient peaks. All of these characteristics make the multiplexer, in effect, a quad switchable high-speed buffer. It requires DC cou- pling and termination resistors when directly driven from a low impedance cable. High-current output amplifiers are recommended when driving low-impedance transmission lines or inputs. An advanced complementary bipolar process, consisting of pn-junction isolated high-frequency NPN and PNP transis- tors, provides wide bandwidth while maintaining low crosstalk and harmonic distortion. The single chip band- width of over 250MHz at an output voltage of 1.4Vp-p allows the design of large crosspoint or distribution fields in HDTV-quality with an overall system bandwidth of 36MHz. The buffer amplifiers also offer low differential gain (0.05%) and phase (0.01 °) errors. These parameters are essential for video applications and demonstrate how well the signal path maintains a constant small-signal gain and phase for the low-level color subcarrier at 4.43MHz (PAL) or 3.58MHz (NSTC) as the brightness (luminance) signal is ramped through its specified range. The bipolar construction also ensures that the input impedance remains high and constant between ON and OFF states. The ON/ OFF input capacitance ratio is near unity, and does not vary with power supply voltage variations. The low output capacitance of 1.5pF when no channel is selected is a very important parameter for large distribution fields. Each par- allel output capacitance is an additional load and reduces the overall system bandwidth. Bipolar video crosspoint switches are virtually glitch-free when compared to signal switches using CMOS or DMOS devices. The MPC100 operates with a fast make-before- break switching action to keep the output switching tran- sients small and short. Switching from one channel to another causes the signal to mix at the output for a short time, but it interferes only minimally with the input signals. |
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