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AD8021 数据表(PDF) 11 Page - Analog Devices |
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AD8021 数据表(HTML) 11 Page - Analog Devices |
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11 / 24 page  Data Sheet AD5545/AD5555 Rev. G | Page 11 of 24 Table 7. AD5545 Control Logic Truth Table1, 2 CS CLK LDAC RS MSB Serial Shift Register Function Input Register Function DAC Register H X H H X No effect Latched Latched L L H H X No effect Latched Latched L + H H X Shift register data advanced one bit Latched Latched L H H H X No effect Latched Latched + L H H X No effect Selected DAC updated with current SR current Latched H X L H X No effect Latched Transparent H X H H X No effect Latched Latched H X + H X No effect Latched Latched H X H L 0 No effect Latched data = 0x0000 Latched data = 0x0000 H X H L H No effect Latched data = 0x8000 Latched data = 0x8000 1 SR = shift register, + = positive logic transition, and X = don’t care. 2 At power-on, both the input register and the DAC register are loaded with all 0s. Table 8. AD5555 Control Logic Truth Table1, 2 CS CLK LDAC RS MSB Serial Shift Register Function Input Register Function DAC Register H X H H X No effect Latched Latched L L H H X No effect Latched Latched L + H H X Shift register data advanced one bit Latched Latched L H H H X No effect Latched Latched + L H H X No effect Selected DAC updated with current SR current Latched H X L H X No effect Latched Transparent H X H H X No effect Latched Latched H X + H X No effect Latched Latched H X H L 0 No effect Latched data = 0x0000 Latched data = 0x0000 H X H L H No effect Latched data = 0x2000 Latched data = 0x2000 1 SR = shift register, + = positive logic transition, and X = don’t care. 2 At power-on, both the input register and the DAC register are loaded with all 0s. POWER-UP SEQUENCE It is recommended to power-up VDD and ground prior to any reference voltages. The ideal power-up sequence is AGNDx, DGND, VDD, VREFx, and digital inputs. A noncompliance power-up sequence can elevate reference current, but the device will resume normal operation once VDD is powered. LAYOUT AND POWER SUPPLY BYPASSING It is a good practice to employ compact, minimum lead length layout design. The input leads should be as direct as possible with a minimum conductor length. Ground paths should have low resistance and low inductance. Similarly, it is also good practice to bypass the power supplies with quality capacitors for optimum stability. Supply leads to the device should be bypassed with 0.01 μF to 0.1 μF disc or chip ceramic capacitors. Low ESR 1 μF to 10 μF tantalum or electrolytic capacitors should also be applied at VDD to minimize any transient disturbance and to filter any low frequency ripple (see Figure 20). Users should not apply switching regulators for VDD due to the power supply rejection ratio degradation over frequency. AD5545/ AD5555 VDD VDD AGNDX DGND 02918- 0- 008 C1 + C2 10 F 0.1 F Figure 20. Power Supply Bypassing and Grounding Connection GROUNDING The DGND and AGNDx pins of the AD5545/AD5555 refer to the digital and analog ground references. To minimize the digital ground bounce, the DGND terminal should be joined remotely at a single point to the analog ground plane (see Figure 20). |
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