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Page 5 of 10

Issue A

LANSDALE Semiconductor, Inc.

ML145159

PIN DESCRIPTIONS

INPUT PINS

OSCin, OSCout

Oscillator Input and Oscillator Output (PDIP, SOG –

Pins 2, 3; SSOP – Pins 7, 8)

These pins form an on–chip reference oscillator when con-

nected to terminals of an external parallel–resonant crystal.

Frequency–setting capacitors of appropriate value must be con-

nected from OSCin to VSS and OSCout toVSS. OSCin may

also serve as input for an externally–generated reference sig-

nal. This signal will typically be AC coupled to OSCin, but for

larger amplitude signals (standard CMOS logic levels), DC

coupling may also be used. In the external reference mode, no

connection is required to OSCout.

fin

Frequency Input (PDIP, SOG – Pin 10, SSOP – Pin 15)

Input to the positive edge triggered divide–by–N and di-

vide–by–A counters. fin is typically derived from a dual–mod-

ulus prescaler and is AC coupled. This input has an inverter

biased in the linear region to allow use with AC coupled sig-

nals as low as 500 mV peak–to–peak or direct coupled signals

swinging from VDD to VSS.

DATA

Serial Data Input (PDIP, SOG – Pin 12, SSOP – Pin 17)

Counter and control information is shifted into this input.

The last data bit entered goes into the one–bit control shift reg-

ister. A logic 1 allows the reference counter information to be

loaded into its 14–bit latch when ENB goes high. A logic 0

entered as the control bit disables the reference counter latch.

The divide–by–A/divide–by–N counter latch is loaded, regard-

less of the contents of the control register, when ENB goes

high. The data entry format is shown in Figure 1.

ENB

Transparent Latch Enable (PDIP, SOG – Pin 13,

SSOP – Pin 18)

A logic high on this input allows data to be entered into the

divide–by–A/divide–by–N latch and, if the control bit is high,

into the reference counter latch. Counter programming is unaf-

fected when ENB is low. ENB should be kept normally low

and pulsed high to transfer data to the latches.

CLK

Shift Register Clock (PDIP, SOG – Pin 11, SSOP – Pin 16)

A low–to–high transition on this input shifts data from the

serial data input into the shift registers.

COMPONENT PINS

CR

Ramp Capacitor (PDIP, SOG – Pin 15, SSOP – Pin 20)

The capacitor connected from this pin to VSS’ is charged lin-

early, at a rate determined by RR. The voltage on this capacitor

is proportional to the phase difference of the frequencies pres-

ent at the internal phase detector inputs. A polystyrene or

mylar capacitor is recommended.

RR

Ramp Current Bias Resistor (PDIP, SOG – Pin 20,

SSOP – Pin 5)

A resistor connected from this pin to VSS’ determines the

rate at which the ramp capacitor is charged, thereby affecting

the phase detector gain (see Figure 2).

CH

Hold Capacitor (PDIP, SOG – Pin 18, SSOP – Pin 3)

The charge stored on the ramp capacitor is transferred to the

capacitor connected from this pin to either VDD’ or VSS’. The

ratio of CR to CH should be large enough to have no effect on

the phase detector gain (CR > 10 CH). A low–leakage capaci-

tor should be used.

RO

Output Bias Current Resistor (PDIP, SOG – Pin 1,

SSOP – Pin 6)

A resistor connected from this pin to VSS’ biases the output

N–Channel transistor, thereby setting a current sink on the ana-

log phase detector output. This resistor adjusts the APDout bias

current (see Figure 3).

OUTPUT PINS

APDout

Analog Phase Detector Output (PDIP, SOG – Pin 17,

SSOP – Pin 2)

This output produces a voltage that controls an external

VCO. The voltage range of this output (VDD = + 9 V) is from

below + 0.5 V to + 8 V or more. The source impedance of this

output is the equivalent of a source follower with an externally

variable source resistor. The source resistor depends upon the

output bias current controlled by the output bias current resis-

tor, RO. The bias current is adjustable from 0.01 mA to 0.5

mA. The output voltage is not more than 1.05 V below the

sampled point on the ramp. With a constant sample of the

ramp voltage at 9 V and the hold capacitor of 50 pF, the instan-

taneous output ripple is about 5 mV peak–to–peak.

Figure 1. Data Entry Format