JAJSCY4D December 2016 – December 2023 DAC38RF80 , DAC38RF83 , DAC38RF84 , DAC38RF85 , DAC38RF90 , DAC38RF93
PRODUCTION DATA
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The DAC38RFxx uses a bandgap reference and control amplifier for biasing the full-scale output current. The DAC full scale output current is set by a combination of the fixed current through the external resistor RBIAS (connected to pin BIASJ) and current from course trim current sources:
The bias current IBIAS through resistor RBIAS is defined by the on-chip bandgap reference voltage VBG (nominally 0.9 V) and control amplifier. For normal operation, it is recommended that RBIAS is set to 3.6 kΩ for a fixed current through RBIAS of 250 µA. This current is scaled 128x internally, giving:
The course trim current sources are configured through SPI register field DACFS in register DACFS (7.5.72),as follows:
From the discussion above, the DAC full scale output current can be configured from 40 mA (DACFS[3:0] = 1111) down to 10 mA (DACFS[3:0] = 0000). In addition to the full scale signal current set by SPI register DACFS (7.5.72), an extra DC bias current is required to set the operating point of the output current sources(Table 7-41).
DACFS (7.5.72) | Signal current (mA) | Total bias current (mA)(1) |
---|---|---|
0 | 10 | 1 |
1 | 12 | 1 |
2 | 14 | 2 |
3 | 16 | 2 |
4 | 18 | 3 |
5 | 20 | 3 |
6 | 22 | 4 |
7 | 24 | 5 |
8 | 26 | 5 |
9 | 28 | 6 |
10 | 30 | 6 |
11 | 32 | 7 |
12 | 34 | 7 |
13 | 36 | 8 |
14 | 38 | 8 |
15 | 40 | 9 |
An external decoupling capacitor CEXT of 0.1 μF should be connected externally to terminal EXTIO for compensation. RBIAS of 3.6 kΩ is recommended for setting the full-scale output current.