AD9851 direct digital synthesizer pinout

The AD9851 combines a programmable 32-bit direct digital synthesizer, 10-bit current-output DAC and comparator. Its reference input can use an internal 6× clock multiplier.

SSOP-28 (RS-28)

28 contacts Current package

Analog Devices · 28-lead shrink small-outline package.

SSOP-28 (RS-28) pinout

Top view. Locate the package index before counting counterclockwise from pin 1.

Selected pin details

18 · AVDD

Supply · Power

Analog supply. Bypass to the local ground plane and use the same nominal voltage as the digital supply.

Analog Devices AD9851 Rev. D, Pin Function Descriptions

Electrical limits · Link to this pin

All 28 pins

Pin	Signal	Direction	Function
1	D3 Input	Input	Bit 3 of the parallel word.
2	D2 Input	Input	Bit 2 of the parallel word.
3	D1 Input	Input	Bit 1 of the parallel word.
4	D0 Input	Input	Bit 0 of the parallel word.
5	PGND Return	Return	Ground return for the 6× clock multiplier.
6	PVCC Supply	Supply	Positive supply for the 6× clock multiplier.
7	W_CLK Input	Input	Rising edge loads a byte in parallel mode or one bit in serial mode.
8	FQ_UD Input	Input	Rising edge commits the input register to the synthesizer.
9	REFCLOCK Input	Input	Master reference input. An enabled 6× multiplier changes the system clock used in tuning calculations.
10	AGND Return	Return	Analog return for the DAC and comparator. Use a common low-impedance ground reference with the digital circuit.
11	AVDD Supply	Supply	Analog supply. Bypass to the local ground plane and use the same nominal voltage as the digital supply.
12	RSET Current-setting node	Current-setting node	Resistor to ground sets the full-scale current of the DAC.
13	VOUTN Output	Output	Complementary logic output of the comparator.
14	VOUTP Output	Output	True logic output of the comparator.
15	VINN Input	Input	Inverting comparator input.
16	VINP Input	Input	Noninverting comparator input.
17	DACBP No connection	No connection	DAC reference node. The data sheet recommends leaving it open for best spectral performance.
18	AVDD Supply	Supply	Analog supply. Bypass to the local ground plane and use the same nominal voltage as the digital supply.
19	AGND Return	Return	Analog return for the DAC and comparator. Use a common low-impedance ground reference with the digital circuit.
20	IOUTB Output	Output	Complementary current output. Match its load to IOUT for best spectral performance.
21	IOUT Output	Output	True sourcing current output. Convert to voltage with a load resistor or transformer.
22	RESET Input	Input	Active-high reset. It sets 0 Hz, 0° phase and parallel programming mode. It does not clear the 40-bit input register.
23	DVDD Supply	Supply	Positive supply for the digital circuitry.
24	DGND Return	Return	Digital circuit ground return.
25	D7 Input	Input	Most significant bit in parallel mode. In serial mode this is the input for the 40-bit stream.
26	D6 Input	Input	Bit 6 of the parallel word.
27	D5 Input	Input	Bit 5 of the parallel word.
28	D4 Input	Input	Bit 4 of the parallel word.

Signal assignments

Serial loading

Reset selects parallel mode. Load the serial-mode enable pattern before clocking a 40-bit stream through D7.

Parallel loading

In parallel mode, transfer five bytes using W_CLK before asserting FQ_UD. Consult the data sheet for the byte order and valid control bits.

Current DAC

Set the full-scale current with RSET. Convert both sourcing current outputs to voltages with matched loads.

Clock comparator

The comparator converts a conditioned analog waveform to complementary logic signals.

Electrical limits

Parameter	Limit	Conditions and source
Single supply2.7–5.25 V	2.7–5.25 V	All positive supply domains must use the same potential. Analog Devices AD9851 Rev. D, Specifications
Maximum direct reference180 MHz at 5 V · 125 MHz at 3.3 V	180 MHz at 5 V · 125 MHz at 3.3 V	Maximum reference frequency depends on the supply. Analog Devices AD9851 Rev. D, Clock Input Characteristics
Frequency incrementSystem clock ÷ 2³²	System clock ÷ 2³²	Use the system clock after any 6× multiplication. Analog Devices AD9851 Rev. D, Theory of Operation
DAC full-scale currentAbout 10 mA	About 10 mA	Set RSET to 3.92 kΩ for the bench fixture. Respect the DAC compliance voltage. Analog Devices AD9851 Rev. D, Pin Function Descriptions

Models and documents

This is the bare RS-28 IC. Breakout modules carry external oscillators, terminations and filter networks that vary by board.

AD9851BRS: RS-28 pinout and package. Check the manufacturer’s ordering guide for packing and grade.
AD9851BRSRL: RS-28 pinout and package. Check the manufacturer’s ordering guide for packing and grade.
AD9851BRSZ: RS-28 pinout and package. Check the manufacturer’s ordering guide for packing and grade.
AD9851BRSZRL: RS-28 pinout and package. Check the manufacturer’s ordering guide for packing and grade.

Analog Devices AD9851 Rev. D· Pin descriptions, electrical and timing data, and serial load sequence.
Analog Devices AD9851 product documentation· Manufacturer product and order code information.
Source register· Document revisions, applicable order codes, consulted sections and available file checksums.