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ISL22511 Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL22511 Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 13 page 10 FN6678.1 July 16, 2009 Power-Up and Down Requirements There are no restrictions on the power-up or power-down conditions of VCC and the voltages applied to the potentiometer pins provided that VCC is always more positive than or equal to VRH and VRL, i.e., VCC ≥ VRH,VRL. The VCC ramp rate specification is always in effect. Pin Descriptions RH and RL The RH and RL pins of the ISL22511 are equivalent to the fixed terminals of a mechanical potentiometer. The minimum voltage is VSS and the maximum is VCC. The terminology of RH and RL references the relative position of the terminal in relation to wiper movement direction. RW The RW pin is the wiper terminal of the potentiometer which is equivalent to the movable terminal of a mechanical potentiometer. PU The debounced PU input is used to increment the wiper position. An on-chip pull-up holds the PU input HIGH. A switch closure to ground or a LOW logic level will, after a debounce time, move the wiper to the next adjacent higher tap position. PD The debounced PD input is used to decrement the wiper position. An on-chip pull-up holds the PD input HIGH. A switch closure to ground or a LOW logic level will, after a debounce time, move the wiper to the next adjacent lower tap position. ASE The debounced ASE (AUTOSTORE enable) pin can be in one of two states: 1. AUTOSTORE is enabled if ASE is held LOW during power up. 2. AUTOSTORE is disabled if ASE is held HIGH during power-up. A LOW to HIGH transition will initiate a manual store operation. This is for the user who wishes to connect a push button switch to this pin. For every valid push, the ISL22511 will store the current wiper position to the EEPROM. Device Operation There are three sections of the ISL22511: the input control, counter and decode section; the EEPROM memory; and the resistor array. The input control section operates just like an up/down counter. The output of this counter is decoded to turn on a single electronic switch, connecting a point on the resistor array to the wiper output. Under the proper conditions, the contents of the counter can be stored in EEPROM memory and retained for future use. The resistor array is comprised of 31 individual resistors connected in series. At either end of the array and between each resistor is an electronic switch that transfers the potential at that point to the wiper. The ISL22511 is designed to interface directly to two push button switches for effectively moving the wiper up or down. The PU and PD inputs increment or decrement a 5-bit counter respectively. The output of this counter is decoded to select one of the thirty-two wiper positions along the resistive array. The wiper increment input, PU and the wiper decrement input, PD are both connected to an internal pull-up so that they normally remain HIGH. When pulled LOW by an external push button 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 PU or PD remain LOW for less than 15ms, typical. Each of the buttons can be pushed either once for a single increment/decrement or continuously for a multiple increments/decrements. The number of increments/decrements of the wiper position depends on how long the button is being pushed. When making a continuous push, after the first second, the increment/decrement speed increases. For the first second, the device will be in the slow scan mode. Then, if the button is held for longer than 1 second, the device will go into the fast scan mode. As soon as the button is released, the ISL22511 will return to a standby condition. If two or more buttons are pressed simultaneously, all commands are ignored upon release of ALL buttons, except Shutdown Mode condition. The wiper, when at either fixed terminal, acts like its mechanical equivalent and does not move beyond the last position. That is, the counter does not wrap around when clocked to either extreme. AUTOSTORE The value of the counter is stored in EEPROM memory after 2 seconds of no activity on PU or PD inputs while ASE is enabled (held LOW). When power is restored, the content of the memory is recalled and the counter resets to the last value stored. If AUTOSTORE is to be implemented, ASE is typically hard wired to VSS. If ASE is held HIGH during power-up and then taken LOW, the wiper will not respond to the PU or PD inputs until ASE is brought HIGH and held HIGH. Manual (Push Button) Store When ASE is not enabled (held HIGH), a push button switch may be used to pull ASE LOW for more than 15ms and released to perform a manual store of the wiper position. During memory write cycle all inputs will be ignored. ISL22511 |
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