DAC8760IPWPR.B datasheet(53/69 Pages) TI2

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11 Layout

11.1 Layout Guidelines

To maximize the performance of the DACx760 in any application, good layout practices and proper circuit design

must be followed. A few recommendations specific to the DACx760 are:

1. As is seen in Figure 9-3, CAP2 is directly connected to the input of the final IOUT amplifier. Any noise or

unwanted ac signal routed near the CAP1 and/or CAP2 pins could capacitively couple onto internal nodes

and affect IOUT. Therefore, with the QFN package, it is important to avoid routing any digital or HART signal

trace over the CAP1 and CAP2 traces.

2. The thermal PAD must be connected to the lowest potential in the system.

3. The +VSENSE connection must be a low-impedance trace connected close to the point of load.

4. AVDD and AVSS must have decoupling capacitors local to the respective pins.

5. The reference capacitor must be placed close to the reference input pin.

6. Avoid routing switching signals near the reference input.

7. For designs that include protection circuits:

a. Place diversion elements, such as TVS diodes or capacitors, close to off-board connectors to make sure

that return current from high-energy transients does not cause damage to sensitive devices.

b. Use large, wide traces to provide a low-impedance path to divert high-energy transients away from I/O

terminals.

11.1.1 Thermal Considerations

The DACx760 is designed for a maximum junction temperature of +150°C. In cases where the maximum AVDD

is driving maximum current into ground, this could be exceeded. Use the following equation, from Section 7.1, to

determine the maximum junction temperature that can be reached:

Power Dissipation = (TJmax – TA)/θJA

(8)

where

• TJmax = 150°C

• TA is the ambient temperature

• θJA is the package dependent junction-to-ambient thermal resistance, which is found in Section 7.4

The power dissipation can be calculated by multiplying all the supply voltages with the currents supplied, which

is found in the Power Requirements subsection of Section 7.5.

Consider an example: IOUT is enabled, supplying 24 mA into GND with a 25°C ambient temperature, AVDD of

24 V, AVSS is tied to GND and DVDD is generated internally. From the specifications table, the maximum value

of AIDD = 3 mA when IOUT is enabled and DAC code = 0x0000. Also, the maximum value of DIDD = 1 mA.

Accordingly, the worst case power dissipation is 24 V × (24 mA + 3 mA + 1 mA) = 672 mW. Using the RθJA value

for the TSSOP package, we get TJmax = 25°C + (32.3 × 0.672)°C = 46.7°C. At 85°C ambient temperature, the

corresponding value of TJmax is 106.7°C. Using this type of analysis, the system designer can both specify and

design for the equipment operating conditions. Note that the thermal pad in both packages is recommended to

be connected to a copper plane for enhanced thermal performance.

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DAC7760, DAC8760

SBAS528D – JUNE 2013 – REVISED DECEMBER 2021

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