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AD5533B Datenblatt(PDF) 11 Page - Analog Devices |
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AD5533B Datenblatt(HTML) 11 Page - Analog Devices |
11 / 16 page REV. A AD5533B –11– TRACK VIN DAC ACQUISITION CIRCUIT VOUT1 BUSY OUTPUT STAGE CONTROLLER THRESHOLD VOLTAGE PIN DRIVER DEVICE UNDER TEST ONLY ONE CHANNEL SHOWN FOR SIMPLICITY AD5533B CONTROLLER OUTPUT STAGE ACQUISITION CIRCUIT Figure 7. Typical ATE Circuit Using TRACK Input FUNCTIONAL DESCRIPTION The AD5533B can be thought of as consisting of an ADC and 32 DACs in a single package. The input voltage VIN is sampled and converted into a digital word. The digital result is loaded into one of the DAC registers and is converted (with gain and offset) into an analog output voltage (VOUT0–VOUT31). Since the chan- nel output voltage is effectively the output of a DAC there is no droop associated with it. As long as power to the device is main- tained, the output voltage will remain constant until this channel is addressed again. To update a single channel’s output voltage, the required new voltage level is set up on the common input pin, VIN. The desired channel is then addressed via the parallel port or the serial port. When the channel address has been loaded, provided TRACK is high, the circuit begins to acquire the correct code to load to the DAC so that the DAC output matches the voltage on VIN. The BUSY pin goes low and remains so until the acquisition is com- plete. The noninverting input to the output buffer is tied to VIN during the acquisition period to avoid spurious outputs while the DAC acquires the correct code. The acquisition is completed in 16 µs max. The BUSY pin goes high and the updated DAC output assumes control of the output voltage. The output voltage of the DAC is connected to the noninverting input of the output buffer. Since the internal DACs are offset by 70 mV (max) from GND, the minimum VIN in ISHA mode is 70 mV. The maximum VIN is 2.96 V due to the upper dead band of 40 mV (max). On power-on, all the DACs, including the offset channel, are loaded with zeros. Each of the 33 DACs is offset internally by 50 mV (typ) from GND so the outputs VOUT0 to VOUT31 are 50 mV (typ) on power-on if the OFFS_IN pin is driven directly by the on-board offset channel (OFFS_OUT), i.e., if OFFS_IN = OFFS_OUT = 50 mV = > VOUT = (Gain VDAC) – (Gain – 1) VOFFS_IN = 50 mV. Analog Input The equivalent analog input circuit is shown in Figure 6. The capacitor C1 is typically 20 pF and can be attributed to pin capaci- tance and 32 off-channels. When a channel is selected, an extra 7.5 pF (typ) is switched in. This capacitor C2 is charged to the previously acquired voltage on that particular channel so it must charge/discharge to the new level. It is essential that the external source can charge/discharge this additional capacitance within 1 µs–2 µs of channel selection so that VIN can be acquired accu- rately. For this reason, a low impedance source is recommended. C1 20pF VIN C2 7.5pF ADDRESSED CHANNEL Figure 6. Analog Input Circuit Large source impedances will significantly affect the performance of the ADC. This may necessitate the use of an input buffer amplifier. Output Buffer Stage—Gain and Offset The function of the output buffer stage is to translate the 50 mV–3 V typical output of the DAC to a wider range. This is done by gaining up the DAC output by 3.52 and offsetting the voltage by the voltage on OFFS_IN pin. V 3.52 V 2.52 V OUT DAC OFFS_IN =× −× VDAC is the output of the DAC. VOFFS_IN is the voltage at the OFFS_IN pin. Table I shows how the output range on VOUT relates to the offset voltage supplied by the user. Table I. Sample Output Voltage Ranges VOFFS_IN (V) VDAC (V) VOUT (V) 0 0.05 to 3 0.176 to 10.56 1 0.05 to 3 –2.34 to +8.04 2.130 0.05 to 3 –5.192 to +5.192 VOUT is limited only by the headroom of the output amplifiers. VOUT must be within maximum ratings. Offset Voltage Channel The offset voltage can be externally supplied by the user at OFFS_IN or it can be supplied by an additional offset voltage channel on the device itself. The required offset voltage is set up on VIN and acquired by the offset DAC. This offset channel’s DAC output is directly connected to OFFS_OUT. By connecting OFFS_OUT to OFFS_IN, this offset voltage can be used as the offset voltage for the 32 output amplifiers. It is important to choose the offset so that VOUT is within maximum ratings. |
Ähnliche Teilenummer - AD5533B_15 |
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Ähnliche Beschreibung - AD5533B_15 |
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