Datasheet

www.ti.com

DAC7574

SLAS375–JUNE 2003

DRIVING RESISTIVE AND CAPACITIVE LOADS

The DAC7574 output stage is capable of driving loads of up to 1000 pF while remaining stable. Within the offset

and gain error margins, the DAC7574 can operate rail-to-rail when driving a capacitive load. Resistive loads of 2

kΩ can be driven by the DAC7574 while achieving a typical load regulation of 1%. As the load resistance drops

below 2 kΩ, the load regulation error increases. When the outputs of the DAC are driven to the positive rail under

resistive loading, the PMOS transistor of each Class-AB output stage can enter into the linear region. When this

occurs, the added IR voltage drop deteriorates the linearity performance of the DAC. This only occurs within

approximately the top 20 mV of the DAC’s digital input-to-voltage output transfer characteristic. The reference

voltage applied to the DAC7574 may be reduced below the supply voltage applied to V

in order to eliminate

this condition if good linearity is a requirement at full scale (under resistive loading conditions).

CROSSTALK

The DAC7574 architecture uses separate resistor strings for each DAC channel in order to achieve ultra-low

crosstalk performance. DC crosstalk seen at one channel during a full-scale change on the neighboring channel

is typically less than 0.5 LSBs. The ac crosstalk measured (for a full-scale, 1 kHz sine wave output generated at

one channel, and measured at the remaining output channel) is typically under -100 dB.

OUTPUT VOLTAGE STABILITY

The DAC7574 exhibits excellent temperature stability of ±3 ppm/°C typical output voltage drift over the specified

temperature range of the device. This enables the output voltage of each channel to stay within a ±25 µV window

for a ±1°C ambient temperature change. Combined with good dc noise performance and true 12-bit differential

linearity, the DAC7574 becomes a perfect choice for closed-loop control applications.

SETTLING TIME AND OUTPUT GLITCH PERFORMANCE

Settling time to within the 12-bit accurate range of the DAC7574 is achievable within 10 µs for a full-scale code

change at the input. Worst case settling times between consecutive code changes is typically less than 2 µs. The

high-speed serial interface of the DAC7574 is designed in order to support up to 188ksps update rate. For

full-scale output swings, the output stage of each DAC7574 channel typically exhibits less than 100 mV of

overshoot and undershoot when driving a 200 pF capacitive load. Code-to-code change glitches are extremely

low (~10 µV) given that the code-to-code transition does not cross an Nx256 code boundary. Due to internal

segmentation of the DAC7574, code-to-code glitches occur at each crossing of an Nx256 code boundary. These

glitches can approach 100 mVs for N = 15, but settle out within ~2 µs. Sufficient bypass capacitance is required

to ensure 10 µs settling under capacitive loading. To observe the settling performance under resistive load

conditions, the power supply (hence DAC7574 reference supply) must settle quicker than the DAC7574.