MP7643AS datasheet(7/12 Pages) EXAR

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MP7643

Rev. 1.00

THEORY OF OPERATION

The MP7643 is a 4-channel multiplying D/A converter that in-

corporates a novel open loop architecture invented by MPS.

The design produces the wider bandwidth, faster settling time,

more constant group delay, and a lower noise operation

compared to the conventional R-2R based architectures. This

device is particularly useful in applications where analog multi-

pliers are used to perform the gain adjustment function for high

frequency analog signal conditioning. Analog multipliers pro-

duce higher noise and offset. This design allows for digital con-

trol of gain with constant and very low noise from the low gain

through high gain ranges of operation.

Linearity Characteristics

Each DAC achieves DNL

+0.5 LSB (typ), INL +1 LSB

(typ), and gain error

+1.5%. Since all 4 channel D/A convert-

ers are fabricated on the same IC, the linearity matching and

gain matching of +0.5% (typ) is achieved.

AC and Transient Settling Characteristics

The novel subranging architecture delivers a 15 MHz (typ.)

–3 dB bandwidth. With all codes = 1 and a 1.6 V step impulse at

VREF(1-4), the analog output settles to 8 bits of accuracy in typi-

cally 150 ns (with RL = 5k to VEE). Also with VREF = 3 V or –3 V

and a FS to ZS or ZS to FS code change, the respective analog

output settles to 8 bits typically in 300 ns. Note that the AC per-

formance specifications also match between all 4 channels.

The above AC and transient performance is achieved with each

channel consuming only 20 mW (typ.) with either

5 V or 0 V to

10 V supplies.

Digital Interface

The MP7643 allows direct interface to most microprocessor

buses without additional I/O circuitry.

Figure 1. and Figure 2.

describe the operation, specification and interface characteris-

tics of the logic port.

The address bits A0 and A1 determine which D/A channel is

selected. When LD input is low the respective latch of the D/A is

enabled (digital input data becomes transparent to the latch and

the selected DAC channel), and digital data is loaded into the se-

lected DAC.

Power Supplies and Voltage Reference DC Voltage

Ranges

For the single supply operation, VCC = +10 V, VDD = +5 V, and

VEE = GND = 0 V. The VOUT 1-4 and VREF 1-4 range would be

VCC –1.8 V (10 – 1.8 = 8.2 V) to VEE +1.5 V (0 + 1.5 = 1.5 V).

VREFN is the equivalent of AGND for this DAC. In this mode

VREFN can be set at (VCC + VEE)/2 = (10 + 0)/2 = 5 V. VREFN DC

range can, however, be set from VEE +1.5 = 1.5 V to VCC – 1.5 =

8.2 V. Refer to

Table 2. for the relationship equations.

For the dual supply operation, VCC = +5, VDD = +5, and VEE =

–5 V. The VOUT 1-4 and VREF 1-4 range would be VCC –1.8 V (5

V –1.8 = 3.2 V) to VEE +1.5 V (–5 + 1.5 = –3.5 V). In this mode

VREFN can be set to (VCC + VEE)/2 = (5 – 5)/2 = 0 V. However,

VREFN DC range can be set from VEE +1.5 V = 3.5 V to VCC –1.8

= +3.2 V. Refer to

Table 2. for the relationship equations.

About the INV Input and its DC Voltage Range

VCC

VOUT 1-4

INV 1-4

VREF 1-4

VREFN

DAC

VEE

Figure 3. Simplified Block Diagram

As noted in the specification table, the max DC value of the

INV input pin is VO. Figure 3. shows a simplified block diagram

of the internal circuitry around INV. If VINV exceeds VO, Q1 will

saturate and the amp and consequently the DAC becomes non-

functional.

The min DC range of INV is limited to Vbe (Q1) and VCE (sat)

of I1. Therefore, INV (min-DC) = VEE +1 V.

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