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SMP9517S Folha de dados(PDF) 3 Page - Summit Microelectronics, Inc. |
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SMP9517S Folha de dados(HTML) 3 Page - Summit Microelectronics, Inc. |
3 / 8 page SMP9517 3 SUMMIT MICROELECTRONICS, Inc. 2035 3.0 5/10/00 There are five main blocks to the SMP9517: an 7-bit EEPROM memory; input debounce circuits, control logic, and 7-bit counter; 7-bit data register; decode section and resistor ladder (DAC); and the buffer amplifier. The input control section operates just like an up/down counter. The output of this counter is fed to the data register and then decoded to activate one of 127 electronic switches connected to the resistor ladder. The ladder is comprised of 128 resistors of equal value connected in series. At the bottom of the ladder and at the junctions of the resistors there are electronic switches that transfer the voltage at each point to the buffer amplifier and then to the output. The SMP9517 is designed to interface directly to two pushbutton switches that effectively move the potentiom- eter wiper up or down. The UP# and DWN# inputs, respectively, increment or decrement the 7-bit counter. The data input to the DAC is decoded to select one of the 128 wiper positions along the resistive ladder. The wiper increment input UP# and the wiper decrement input DWN# are connected to internal pull-ups so that they normally remain high. When pulled low by an external pushbutton switch or a logic low level input, the wiper will be switched to the next adjacent tap position. Internal debounce circuitry prevents inadvertent switching of the wiper position if UP# or DWN# remain low for less than 30ms (typical). Each of the buttons can be pushed either once for a single increment/decrement or held low continuously for multiple increments/decrements. The number of increments/dec- rements of the wiper position depends on how long the button is pushed. When making a continuous push, after the first second, the increment/decrement speed in- creases. For the first second the device will be in the slow scan mode. Then, if the button is held for longer than one second, the device will go into the fast scan mode. As soon as the button is released the SMP9517 will return to a standby condition. The DAC, whether set to 00HEX or FFHEX, acts like its mechanical equivalent and does not move beyond the last position. That is, the counter does not wrap around when clocked up to FFHEX or down to 00HEX. AUTOSTORE The value of the counter is stored in EEPROM memory whenever the chip senses a power-down of VDD while STR# is enabled (held low). When power is restored the contents of the memory are recalled and the counter reset to the last value stored. If AUTOSTORE is to be imple- mented, STR# is typically hard wired to GND. If STR# is held high during power-up and then taken low the wiper will not respond to the UP# or DWN# inputs until STR# is brought high and the store is complete. See Figure 1. Manual (Pushbutton) Store When STR# is not enabled (held high) a pushbutton switch may be used to pull STR# low and released to perform a manual store of the wiper position in EEPROM memory. See Figure 2. Effect of VDD Removal The resistor ladder, connected between VH and VL, does not change value when VDD is removed. However, the buffer amplifier no longer functions, and consequently a high impedance appears at the VOUT pin. Figure 2: Typical circuit with STR store pin controlled by push button switch Figure 1: Typical circuit with STR store pin used in AUTOSTORE mode DEVICE OPERATION UP# DWN# VH GND VDD STR# VL VOUT 8 7 6 5 1 2 3 4 VDD 3.3µF 2035 T Fig01 3.0 UP# DWN# VH GND VDD STR# VL VOUT 8 7 6 5 1 2 3 4 VDD 20k Ω 2035 T Fig02 3.0 |
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Descrição semelhante - SMP9517S |
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