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LTC2634HMSE-LZ8 数据表(PDF) 22 Page - Linear Technology |
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LTC2634HMSE-LZ8 数据表(HTML) 22 Page - Linear Technology |
22 / 30 page LTC2634 22 2634fb OPERATION Power-Down Mode For power-constrained applications, power-down mode can be used to reduce the supply current whenever less than four DAC outputs are needed. When in power down, the buffer amplifiers, bias circuits, and integrated reference circuits are disabled, and draw essentially zero current. The DAC outputs are put into a high impedance state, and the output pins are passively pulled to ground through individual 200k resistors. Input- and DAC-register contents are not disturbed during power down. Any DAC channel or combination of channels can be put into power-down mode by using command 0100b in combination with the appropriate DAC address, (n). The supply current is reduced approximately 20% for each DAC powered down. The integrated reference is automatically powered down when external reference is selected using command 0111b. In addition, all the DAC channels and the integrated reference together can be put into power- down mode using power-down chip command 0101b. When the integrated reference and all DAC channels are in power-down mode, the REF pin becomes high imped- ance (typically > 1GΩ). For all power-down commands the 16-bit data word is ignored. Normal operation resumes after executing any command that includes a DAC update, (as shown in Table 1) or pull- ing the asynchronous LDAC pin low. The selected DAC is powered up as its voltage output is updated. When a DAC which is in a powered-down state is powered up and updated, normal settling is delayed. If less than four DACs are in a powered-down state prior to the update command, the power-up delay time is 10μs. However, if all four DACs and the integrated reference are powered down, then the main bias generation circuit block has been automatically shut down in addition to the DAC amplifiers and reference buffers. In this case, the power-up delay time is 12μs. The power-up of the integrated reference depends on the command that powered it down. If the reference is powered down using the select external reference com- mand (0111b), then it can only be powered back up using select internal reference command (0110b). However, if the reference was powered down using power-down chip command (0101b), then in addition to select internal reference command (0110b), any command (in software or using the LDAC pin) that powers up the DACs will also power up the integrated reference. Voltage Output The LTC2634’s integrated rail-to-rail amplifier has guaran- teed load regulation when sourcing or sinking up to 10mA at 5V, and 5mA at 3V. Load regulation is a measure of the amplifier’s ability to maintain the rated voltage accuracy over a wide range of load current. The measured change in output voltage per change in forced load current is expressed in LSB/mA. DC output impedance is equivalent to load regulation, and may be derived from it by simply calculating a change in units from LSB/mA to ohms. The amplifier’s DC output impedance is 0.1Ω when driving a load well away from the rails. When drawing a load current from either rail, the output voltage headroom with respect to that rail is limited by the 50Ω typical channel resistance of the output devices (e.g., when sinking 1mA, the minimum output voltage is 50Ω • 1mA, or 50mV). See the graph “Headroom at Rails vs Output Current” in the Typical Performance Character- istics section. The amplifier is stable driving capacitive loads of up to 500pF. |
类似零件编号 - LTC2634HMSE-LZ8 |
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类似说明 - LTC2634HMSE-LZ8 |
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