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MPC104AU Datasheet(PDF) 9 Page - Burr-Brown (TI) |
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MPC104AU Datasheet(HTML) 9 Page - Burr-Brown (TI) |
9 / 15 page ® MPC104 9 APPLICATIONS INFORMATION The MPC104 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 As shown below, all pins on the MPC104 are internally protected from ESD by a pair of back-to-back reverse-biased diodes to either power supply. 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 continuous current of 30mA without destruction. To insure long term reliability, however, diode current should be externally lim- ited to 10mA 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 the characteristics of the buffer amplifier input without necessarily destroying the device. In precision buffer ampli- fiers, such damage may cause a noticeable degradation of offset voltage and drift. Therefore, static protection is strongly recommended when handling the MPC104. Static damage has been well-recognized as a problem for MOSFET devices, but any semiconductor device deserves protection from this potentially damaging source. The MPC104 incorporates on-chip ESD protection diodes as shown in Figure 1. Thus the user does not need to add external protection diodes, which can add capacitance and degrade AC performance. DISCUSSION OF PERFORMANCE The MPC104 is a 2 x 1, wide-band analog signal multi- plexer. It allows the user to connect one of the two inputs (IN 1/IN2 ) to the output. The switching speed between two input channels is typically less than 300ns. However, in contrast to signal switches using CMOS or DMOS transistors, the switching transients were kept very FIGURE 1. Internal ESD Protection. –V CC +V CC ESD Protection diodes internally connected to all pins. Internal Circuitry External Pin low at +13mV and –4mV. The MPC104 consists of two identical unity-gain buffer amplifiers, respectively connected together internally at the output. The open-loop buffer amps, which consist of complementary emitter followers, apply no feedback so their low-frequency gain is slightly less than unity and somewhat dependent on loading. Unlike devices using MOS bilateral switching elements, the bipolar comple- mentary buffers form a unidirectional transmission path, thus providing high output-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 outputs of the device are high-impedance and allow the user to wire several MPC104s together to create multichannel switch matrices. 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 selection monitoring for the user, and lowers transient peaks. All of these characteristics make the multiplexer, in effect, a quad switchable high-speed buffer. The buffers require DC coupling and termination resistors when driven directly 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 210MHz at an output voltage of 1.4Vp-p allows the design of multi-channel crosspoint or distribution fields in HDTV-quality with an overall system bandwidth of 36MHz, or in quality for high resolution graphic and imag- ing systems with 200MHz system bandwidth. The buffer amplifiers also offer low differential gain (0.03%) and phase (0.01 °) errors. These parameters are essential for video applications and demonstrate how well the signal path main- tains a constant small-signal gain and phase for the low-level color subcarrier at 4.43MHz (PAL) or 3.58MHz (NSTC) as the luminance signal is ramped through its specified range. The bipolar construction also ensures that the input imped- ance 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 1.2pF when no channel is selected is a very important parameter for large distribution fields. Each parallel 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 MPC104 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 hardly interferes with the input signals. The transient peaks remain less than +13mV and –4mV. The generated output transients are extremely small, so DC clamping during switching between channels is unneces- sary. DC clamping during the switching dead time is re- |
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