87LPC769 datasheet(16/61 Pages) PHILIPS

16 / 61 page

Philips Semiconductors

Preliminary specification

87LPC769

Low power, low price, low pin count (20 pin)

microcontroller with 4 kB OTP 8-bit A/D, and DAC

2001 Jan 11

Digital to Analog Converter (DAC) Outputs

The 87LPC769 provides a two channel, 8-bit DAC function. DAC0 is

also a part of the A/D Converter and it should not be enabled while

the A/D is active. Digital outputs must be disabled on the DAC

output pins while the corresponding DAC is enabled, as described in

the section Analog Functions.

The DACs use the power supply as the references: VDD as the

upper reference and VSS as the lower reference. The DAC output is

generated by a tap from a resistor ladder and is not buffered. The

maximum resistance to VDD or VSS from a DAC output is 10kΩ.

Care must be taken with the loading of the DAC outputs in order to

avoid distortion of the output voltage. DAC accuracy is affected by

noise generated on-chip and elsewhere in the application. Since the

87LPC769 power pins are used for the DAC references, the power

supply also affects the accuracy of the DAC outputs.

The ideal DAC output may be calculated as follows:

Result

+ (DAC Value ) 0.5)

DD * VSS

256

where DAC value is the contents of the relevant DAC register:

DAC0 or DAC1.

SU01371

D/A CONVERTER

ENDACn

VREF+ = VDD

DACn pin

VREF– = Vss

ADCON

DACn

Figure 4. DAC Block Diagram

87LPC769 Datasheet(PDF) 16 Page - NXP Semiconductors