Operation of ACBUF is controlled by register ACEN. When ACEN=0, the op amp is turned off and

the output is in high impedance.

The gain of ACBUF is set by control register ACDIV. When ACDIV=0, the gain is 1. When ACDIV=1, the gain of

the op amp is determined by the external resistance.

2) RCTOP Op Amp

RCTOP op amp is enabled by control register RCTEN. When RCTEN=0, the op amp is turned off to save

power.

Ohm Voltage Source

The supplied voltages of the Ohm voltage source are shown in Table 14 and they are directly fed into the

attenuating network. The output of the Ohm voltage source is controlled by SOSR1:0. The value of SOSR1:0

can be directly set by the control register.

When the output of the Ohm voltage source is VDD, the switch resistor in the loop will affect the voltage of the

chip driving terminator. Therefore, the load affects the effective load voltage.

Because of the high gain op amp and negative feedback, outputs other than VDD will not be affected by the

switch resistor. The effect of load in the circuit can be neglected, and the maximum supplied current is around



1.2mA.

Table 14. Control Values of the Ohm Voltage Source

INPUT

OUTPUT

MODE3:0

SOSR1:0

OSRO

1001

00

high impedance

1001

01

AX5

1001

10

Vrfh

1001

11

VDD