ADF4252BCPZ-R7 datasheet(24/30 Pages) AD

24 / 30 page

ADF4252

Data Sheet

Rev. E | Page 24 of 30

RF Charge Pump Three-State

This bit puts the charge pump into three-state mode when

programmed to a 1. It must be set to 0 for normal operation.

RF Power-Down

DB5 on the ADF4252 provides the programmable power-down

mode. Setting this bit to a 1 performs a power-down on both

the RF and IF sections. Setting this bit to 0 returns the RF and

IF sections to normal operation. While in software power-

down, the device retains all information in its registers. Only

when supplies are removed are the register contents lost.

When a power-down is activated, the following events occur:

All active RF dc current paths are removed.

The RF synthesizer counters are forced to their load state

conditions.

The RF charge pump is forced into three-state mode.

The RF digital lock detect circuitry is reset.

The RFIN input is debiased.

The input register remains active and capable of loading

and latching data.

RF Phase Detector Polarity

DB7 on the ADF4252 sets the RF phase detector polarity. When

the VCO characteristics are positive, this bit must be set to 1.

When VCO characteristics are negative, this bit must be set to 0.

RF Charge Pump Current Setting

DB9 and DB10 set the RF charge pump current setting. This

must be set to whatever charge pump current the loop filter has

been designed with (see Figure 37).

RF Test Modes

These bits must be set to 000 for normal operation.

MASTER REGISTER (ADDRESS R3)

With Bits[2:0] of R3 set to 011, the on-chip master register

is programmed. Figure 38 shows the input data format for

programming the master register.

RF and IF Counter Reset

DB3 is the counter reset bit for the ADF4252. When this bit is 1,

both the RF and IF R, INT, and MOD counters are held in reset.

For normal operation, this bit must be 0. Upon power-up, the

DB3 bit must be disabled, and the INT counter resumes counting

in close alignment with the R counter (the maximum error is

one prescaler cycle).

Charge Pump Three-State

This bit puts both the RF and IF charge pump into three-state

mode when programmed to a 1. It must be set to 0 for normal

operation.

Power-Down

Bit 3 of R3 on the ADF4252 provides the programmable power-

down mode. Setting this bit to a 1 performs a power-down on

both the RF and IF sections. Setting this bit to 0 returns the RF

and IF sections to normal operation. While in software power-

down, the device retains all information in its registers. Only

when supplies are removed are the register contents lost.

When a power-down is activated, the following events occur:

All active dc current paths are removed.

The RF and IF counters are forced to their load state

conditions.

The RF and IF charge pumps are forced into three-state mode.

The digital lock detect circuitry is reset.

The RFIN input and IFIN input are debiased.

The oscillator input buffer circuitry is disabled.

The input register remains active and capable of loading

and latching data.

XO Disable

Setting this bit to 1 disables the REFOUT circuitry. This is set to 1

when using an external TCXO, VCXO, or other reference

sources. This is set to 0 when using the REFIN and REFOUT pins

to form an oscillator circuit.

MUXOUT Control

The on-chip multiplexer is controlled by Bits[10: 7] of R3 on the

ADF4252. Figure 38 shows the truth table.

If the user updates the RF control register or the IF control

MUXOUT signal, the user must write to the master register.

Lock Detect

The digital lock detect output goes high if there are 40 successive

PFD cycles with an input error of less than 15 ns. It stays high

until a new channel is programmed or until the error at the

PFD input exceeds 30 ns for one or more cycles. If the loop

bandwidth is narrow compared to the PFD frequency, the error

at the PFD inputs may drop below 15 ns for 40 cycles around a

cycle slip; therefore, the digital lock detect may go falsely high

for a short period until the error again exceeds 30 ns. In this case,

the digital lock detect is reliable only as a loss of lock indicator.

IF N DIVIDER REGISTER (ADDRESS R4)

With Bits[2:0] of R4 set to 100, the on-chip IF N divider register

is programmed. Figure 39 shows the input data format for

programming this register.

IF CP Gain

When set to 1, this bit changes the IF charge pump current

setting to its maximum value. When the bit is set to 0, the

charge pump current reverts back to its previous state.

IF Prescaler

The dual-modulus prescaler (P/P + 1), along with the IF A and

IF B counters, determine the overall division ratio, N, to be

realized (N = PB + A) from the IFIN to the IF PFD input.

Operating at CML levels, the prescaler takes the clock from the

IF input stage and divides it down to a manageable frequency

for the CMOS counters. It is based on a synchronous 4/5 core.

See Equation 2 and Figure 39.

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