Analog Integrated Circuit Device Data

Freescale Semiconductor

13

33099

TYPICAL APPLICATIONS

Normally the programmable divider Np divides frequency

frequency as input to the U/D counter. Divide ratio N can be

pre-selected by the user for four different divide ratios by

switching a combination of the LRC1 and LRC2 normally

LRC pin to ground is about 45

µA. The phase frequency f

ph

and an up/down (u/d) state on a u/d line from the up/down

control switch determines ratio N. In the LRC mode when

LRC2 pin combinations produce N divide ratios of 66, 132,

198, and 264. When the u/d line is in the down, or low, state,

line.

The u/d line from the up/down control switch determines

the direction of the count as well as the divide ratio N. For an

up state on the u/d line, the output of the 4-bit U/D counter

increments up at a rate of 5.98 Hz (count change every

167 ms) for N=66, 2.99 Hz (count change every 334 ms) for

N=132, 1.99 Hz (count change every 502 ms) for N = 198, or

1.496 Hz (count change every 671 ms) for N = 264. For a

down state on the u/d line, the output of the 4-bit U/D counter

decrements at a rate of about 99 Hz (count decrement about

every 10 ms). The 4-bit output lines of the up/down counter

are coupled as control inputs of the MUX.

The MUX couples one of the 11 digital duty cycle input

lines to the MUX output dependent upon the 4-bit control

inputs from the U/D counter. When the MUX control input

count is 0, the first 31.25% digital duty cycle is selected and

provided at the MUX output. When the control input count is

10, the eleventh 93.75% digital duty cycle is selected at

output of the MUX. A MUX control input of 11 produces a

100% duty cycle at the MUX output. Thus each of the MUX

input lines is selected and provided at the MUX output and

incremented to the next line at a rate dependent on the rate

the MUX control inputs increment. For an up state on the u/d

line, the digital duty cycle at the output of the MUX will

increment from 31.24% to 100% in 11 steps at a rate from

dependent on the LRC1 and LRC2 pin terminations. For a

down state on the u/d line, the digital duty cycle will count

down at a rate of about 10 ms/step change.

The A/D duty cycle comparator and tracking circuit

digital duty cycle from the MUX output. The A/D duty cycle

comparator provides a high, or up (u), output when the

analog duty cycle is greater than the digital duty cycle, and a

low, or down (d), output when the analog duty cycle is less

than the digital duty cycle.

down control switch enables the u/d output of the A/D duty

cycle comparator to be coupled to the u/d line. In the steady

state, the A/D duty cycle comparator will provide an u/d input

to the U/D counter and Np divider to increase or decrease the

digital duty cycle to track the analog duty cycle. If the analog

duty cycle increases to a value greater than the digital duty

cycle at a rate that is greater than the selected LRC digital

duty cycle rate, the A/D duty cycle comparator will output an

up signal on the u/d line to cause the digital duty cycle to

increase to the analog duty cycle at the selected LRC digital

duty cycle rate. If the analog duty cycle decreases to a value

less than the digital duty cycle, the A/D duty cycle comparator

will output a down signal on the u/d line to cause the digital

duty cycle to decrease to the analog duty cycle at a fixed rate

of about 10 ms/step. For an analog duty cycle less than

31.25%, the down count at the output of the U/D counter will

remain at 0 and the digital duty cycle will remain at 31.25%.

up/down control switch will provide a down signal on the u/d

line independent of the duty cycle comparator u/d output. The

will cause the digital duty cycle to be constant at 31.25% and

U/D counter.

When approximately 5.0 V is applied to the LRC TEST pin,

LRC function is accelerated by a factor of 16, which allows

the testing of all LRC associated rates to be accelerated by a

factor of 16. During normal LRC operation, the LRC pin is in

a low ground state, having an internal 10 k

Ω pull-down

resistor.

The duty cycle output of the AND3 GATE reflects the

minimum duty cycle at the AND3 GATE inputs. Thus when

the analog duty cycle exceeds the digital duty cycle, the

digital duty cycle becomes the controlling duty cycle at the

AND3 GATE output. When the analog duty cycle is less than

the digital duty cycle, the analog duty cycle becomes the

controlling duty cycle at the AND3 GATE output. Thus in the

the analog duty cycle from 0% to 100% will cause the duty

cycle at the output of the AND3 GATE to increase rapidly

from 0% to 31.25% and then increase slowly at the LRC rate

from 31.25% to 100%. If the analog duty cycle provides a

step increase from a duty cycle greater than 31.25%, then the

resulting LRC duty cycle increase from the initial analog duty

cycle at the output of the AND3 GATE. For a decreasing step

response in the analog duty cycle, the output of the AND3

GATE will rapidly follow the decreasing analog duty cycle.

The output of the AND3 GATE drives the GATE output (and

the field current) through an OR1 GATE, an AND4 GATE,

and switch S3. Thus the minimum GATE LRC duty cycle

A 0% analog duty cycle will produce a 0% duty cycle at the

output of the AND3 GATE. However, the output of the AND3

GATE is ORed with a 3.1% minimum duty cycle signal from

the minimum duty cycle generation at the OR1 GATE input to

provide a minimum 3.1% duty cycle to the AND4 GATE input.

This provides the resulting minimum GATE duty cycle

duty cycle is 0%.