Analog Devices AD9883A Pixel Clock Range VCO Gain, PV1 PV0, MHz MHz/V, Ip2 Ip1 Ip0 Current a

AD9883A

The PLL characteristics are determined by the loop filter design, by the PLL Charge Pump Current and by the VCO range setting. The loop filter design is illustrated in Figure 6. Recommended settings of VCO range and charge pump current for VESA standard display modes are listed in Table V.

PVD

CP 0.0039￿F	0.039￿F CZ
	3.3k￿ RZ

FILT

Figure 6. PLL Loop Filter Detail

Four programmable registers are provided to optimize the per- formance of the PLL. These registers are:

1.The 12-Bit Divisor Register. The input Hsync frequencies range from 15 kHz to 110 kHz. The PLL multiplies the frequency of the Hsync signal, producing pixel clock frequencies in the range of 12 MHz to 110 MHz. The Divisor Register controls the exact multiplication factor. This register may be set to any value between 221 and 4095. (The divide ratio that is actually used is the programmed divide ratio plus one.)

2.The 2-Bit VCO Range Register. To improve the noise performance of the AD9883A, the VCO operating frequency range is divided into three overlapping regions. The VCO Range Register sets this operating range. The frequency ranges for the lowest and highest regions are shown in Table II.

Table II. VCO Frequency Ranges

		Pixel Clock Range	KVCO Gain
PV1	PV0	(MHz)	(MHz/V)
0	0	12–36	150
0	1	36–72	150
1	0	72–110	150
1	1	110-140	150

3.The 3-Bit Charge Pump Current register. This register allows the current that drives the low pass loop filter to be varied. The possible current values are listed in Table III.

Table III. Charge Pump Current/Control Bits

Ip2	Ip1	Ip0	Current (￿A)
0	0	0	50
0	0	1	100
0	1	0	150
0	1	1	250
1	0	0	350
1	0	1	500
1	1	0	750
1	1	1	1500

4.The 5-Bit Phase Adjust Register. The phase of the generated sampling clock may be shifted to locate an optimum sampling

point within a clock cycle. The Phase Adjust register provides 32 phase-shift steps of 11.25° each. The Hsync signal with an identical phase shift is available through the HSOUT pin.

The COAST pin is used to allow the PLL to continue to run at the same frequency, in the absence of the incoming HSYNC signal or during disturbances in Hsync (such as equalization pulses). This may be used during the vertical sync period, or any other time that the HSYNC signal is unavailable. The polarity of the COAST signal may be set through the Coast Polarity Register. Also, the polarity of the HSYNC signal may be set through the HSYNC Polarity Register. For both HSYNC and COAST, a value of “1” is active high.

Power Management

The AD9883A uses the activity detect circuits, the active inter- face bits in the serial bus, the active interface override bits, and the power-down bit to determine the correct power state. There are three power states, full-power, seek mode, and power-down. Table IV summarizes how the AD9883A determines what power mode to be in and what circuitry is powered on/off in each of these modes. The power-down command has priority and then the automatic circuitry.

Table IV. Power-Down Mode Descriptions

	Inputs
	Power-	Sync	Powered On or
Mode	Down1	Detect2	Comments
Full-Power	1	1	Everything
Seek Mode	1	0	Serial Bus, Sync
			Activity Detect,
SOG,
			Bandgap Reference
Power-Down	0	X	Serial Bus, Sync
			Activity Detect, SOG,
			Bandgap Reference

NOTES

1Power-Down is controlled via Bit 1 in serial bus register 0Fh.

2Sync Detect is determined by OR-ing Bits 7, 4, and 1 in serial bus register 14h.

–10– REV. 0