AD1990

Rev. 0 | Page 14 of 16

Using a Crystal Oscillator

Clocking Multiple Amplifiers in Parallel

The AD1990 can use a crystal connected to the CLKI and

CLKO pins as a master clock source, as shown in Figure 25. The

CLKI and CLKO pins connect to an internal inverter to create a

full resonator. The typical values shown work in many applications,

but the crystal manufacturer should provide the exact type and

value of the capacitors and the resistor.

If there are multiple AD199x family amplifiers connected to the

derivatives) for each amplifier as previously described. Avoid

clocking amplifiers from similar but asynchronous clocks if

they use the same power supply because this can result in beat

frequencies.

22pF

22pF

XTAL

47Ω

PROTECTION CIRCUITS AND ERROR REPORTING

Thermal Protection

The AD1990 features thermal protection. When the die

temperature exceeds approximately 135°C, the thermal warning

error output (ERR1) is asserted. If the die temperature exceeds

approximately 150°C, the thermal shutdown error output

(ERR2) is asserted. If this occurs, the part shuts down to

prevent damage to the part. When the die temperature drops

below approximately 120°C, the part returns to normal

operation automatically and negates both error outputs.

Figure 25. Crystal Connection

Using an External Clock Source

If a clock signal of the appropriate frequency already exists in

the application circuit, connect it directly to CLKI and leave

CLKO floating. The logic levels of the square wave should be

compatible with those defined in Specifications section.

Overcurrent Protection

The AD1990 features over current or short-circuit protection. If

the current through any power transistors exceeds approximately

4 A, the part enters a mute state and the overcurrent error

output (ERR0) is asserted. This is a latched error and does not

clear automatically. Restore normal operation and clear the

error condition by either asserting and then negating RESET or

by asserting and then negating MUTE.

Large amounts of jitter on the clock input degrade performance.

Whenever possible, avoid passing the clock signal through

programmable logic and other circuits with unknown or variable

propagation delay. In general, clock signals suitable for audio ADCs

or DACs are also appropriate for use with the AD1990.