ANALOG DEVICES AD1555, AD1556 Service Manual

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AD1555
a	24-Bit - ADC
a	with Low Noise PGA

FEATURES AD1555

Fourth Order - Modulator

Large Dynamic Range

116 dB Min, 120 dB Typical @ 1 ms

117 dB Typical @ 0.5 ms

Low Input Noise: 80 nV rms @ 4 ms with Gain of 34,128

Low Distortion: –111 dB Max, –120 dB Typical Low Intermodulation: 122 dB

Sampling Rate at 256 kSPS

Very High Jitter Tolerance

No External Antialias Filter Required Programmable Gain Front End

Input Range: 2.25 V

Robust Inputs

Gain Settings: 1, 2.5, 8.5, 34, 128 Common-Mode Rejection (DC to 1 kHz)

93 dB Min, 101 dB Typical @ Gain of 1 77 mW Typical Low Power Dissipation Standby Modes

AD1556

FIR Digital Filter/Decimator

Serial or Parallel Selection of Configuration Output Word Rates: 250 SPS to 16 kSPS 6.2 mW Typ Low Power Dissipation

70 W in Standby Mode

Reference Design and Evaluation Board with Software Available

APPLICATIONS

Seismic Data Acquisition Systems

Chromatography

Automatic Test Equipment

GENERAL DESCRIPTION

The AD1555 is a complete sigma-delta modulator, combined with a programmable gain amplifier intended for low frequency,

AD1555/AD1556

high dynamic range measurement applications. The AD1555 outputs a ones-density bitstream proportional to the analog input. When used in conjunction with the AD1556 digital filter/ decimator, a high performance ADC is realized.

The continuous-time analog modulator input architecture avoids the need for an external antialias filter. The programmable gain front end simplifies system design, extends the dynamic range, and reduces the system board area. Low operating power and standby modes makes the AD1555 ideal for remote battery-pow- ered data acquisition systems.

The AD1555 is fabricated on Analog DevicesÕ BiCMOS process that has high performance bipolar devices along with CMOS transistors. The AD1555 and AD1556 are packaged, respectively, in 28-lead PLCC and 44-lead MQFP packages and are specified from Ð55°C to +85°C (AD1556 and AD1555 B Grade) and from 0°C to 85°C (AD1555 A Grade).

–20

fIN = 24.4Hz

SNR = 116.7dB

–40

THD = –120.6dB

– dBr

–60

–80

AMPLITUDE

–100

–120

–140

–160

–180

–200

100

150

200

250

300

350

400

450

500

FREQUENCY – Hz

Figure 1. FFT Plot, Full-Scale AIN Input, Gain of 1

FUNCTIONAL BLOCK DIAGRAM

		REFIN	REFCAP2	REFCAP1	AGND3
						MODE CONTROL
		REF DIVIDER				LOGIC
				DAC		OVERVOLTAGE
				DAC		DETECTION
						DETECTION
		PGA		LOOP
				LOOP
AIN (+)	MUX			FILTER
AIN (+)	MUX
AIN (–)
TIN (+)						CLOCK
TIN (–)				AD1555		GENERATION
TIN (–)				AD1555
	AGND1	PGAOUT	MODIN AGND2 +VA		–VA	VL DGND

REV. B

	PGA0...PGA4	H/S	ERROR
CB0...CB4	PGA	CONFIGURATION		INPUT SHIFT
	PGA	CONFIGURATION		INPUT SHIFT	DIN
	CONTROL	REGISTER		REGISTER	DIN
	CONTROL	REGISTER		REGISTER
MFLG					SCLK
MFLG			STATUS		CS
			STATUS		CS
			REGISTER		R/W
CSEL					R/W
CSEL				DATA
	INPUT	DIGITAL		DATA	DOUT
TDATA	INPUT	DIGITAL		OUTPUT
TDATA	MUX	FILTER		OUTPUT
	MUX	FILTER		MUX
				MUX
MDATA			DATA		DRDY
			DATA
	CLOCK DIVIDER		REGISTER		RSEL
MCLK	CLOCK DIVIDER		AD1556
MCLK

	CLKIN SYNC	BW0...BW2 RESET PWRDN GND			VL

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700	www.analog.com
Fax: 781/326-8703	© Analog Devices, Inc., 2002

AD1555/AD1556

AD1555–SPECIFICATIONS

(+VA = +5 V; –VA = –5 V; VL = 5 V; AGND = DGND = 0 V; MCLK = 256 kHz; TA = TMIN to TMAX, unless otherwise noted.)

		AD1555BP			AD1555AP
Parameter	Notes	Min	Typ	Max	Min	Typ	Max	Unit

PGA Gain Settings	1, 2.5, 8.5, 34, 128

AC ACCURACY
Dynamic Range1	PGA Gain of 1	116.5	120		116	120		dB
	PGA Gain of 2.5	116	119.5		115.5	119.5		dB
	PGA Gain of 8.5	114	117.5		114	117.5		dB
	PGA Gain of 34	104.5	109.5		104.5	109.5		dB
Total Harmonic Distortion2	PGA Gain of 128		98			98		dB
Total Harmonic Distortion2	PGA Gain of 1		Ð120	Ð111		Ð120	Ð107	dB
	PGA Gain of 2.5		Ð116	Ð108		Ð116	Ð107	dB
	PGA Gain of 8.5		Ð116	Ð106		Ð116	Ð105	dB
	PGA Gain of 34		Ð115	Ð101		Ð115	Ð101	dB
Jitter Tolerance3	PGA Gain of 128		Ð108			Ð108		dB
Jitter Tolerance3				300			300	ps
Intermodulation Distortion4	PGA Gain of 1		122			122		dB
DC ACCURACY
Absolute Gain Error5	PGA Gain of 1, 2.5	Ð3.5		+3.5	Ð3.5		+3.5	%
	PGA Gain of 8.5	Ð4.5		+4.5	Ð4.5		+4.5	%
	PGA Gain of 34	Ð10		+10	Ð10		+10	%
Gain Stability Over Temperature5			± 15			± 15		ppm/°C
Offset5, 6	All PGA Gain		Ð60			Ð60		mV
Offset Drift5, 6			6			6		µV/°C
ANALOG INPUT				± 2.25			± 2.25
Full-Scale Nondifferential Input	MODIN			± 2.25			± 2.25	V
Input Impedance	MODIN		20	± 2.25		20	± 2.25	k
Full-Scale Differential Input	PGA Gain of 1			± 2.25			± 2.25	V
	Other PGA Gain Settings		See Table I		See Table I			MΩ
Differential Input Impedance	AIN, TIN Inputs		140	± 2.25		140	± 2.25	MΩ
Common-Mode Range	VCM = ± 2.25 V, fIN = 200 Hz			± 2.25			± 2.25	V
Common-Mode Rejection Ratio	VCM = ± 2.25 V, fIN = 200 Hz
	PGA Gain of 1	93	101		91	101		dB
	PGA Gain of 2.5	95	102		91.5	102		dB
	PGA Gain of 8.5, 34	95.5	108		94.5	108		dB
Power Supply Rejection Ratio7	PGA Gain of 128		108			108		dB
Power Supply Rejection Ratio7			50			50		dB
AIN to TIN Crosstalk Isolation	fIN = 200 Hz		130			130		dB
Differential Input Current			130			130		nA

TEMPERATURE RANGE8								°C
Specified Performance	TMIN to TMAX	Ð55		+85	0		85	°C
REFERENCE INPUT9
Input Voltage Range		2.990	3.0	3.010	2.990	3.0	3.010	V
Input Current			130			130		µA

DIGITAL INPUTS OUTPUTS
VIL		Ð0.3		+0.8	Ð0.3		+0.8	V
VIH		2.0		VL + 0.3	2.0		VL + 0.3	V
IIL		Ð10		+10	Ð10		+10	µA
IIH		Ð10		+10	Ð10		+10	µA
VOL	ISINK = +2 mA			0.4			0.4	V
VOH	ISOURCE = Ð2 mA	2.4			2.4			V

–2–

REV. B

AD1555/AD1556

			AD1555BP			AD1555AP
Parameter	Notes	Min	Typ	Max	Min	Typ	Max	Unit

POWER SUPPLIES
Recommended Operating Conditions
+VA		4.75	5	5.25	4.75	5	5.25	V
ÐVA		Ð5.25	Ð5	Ð4.75	Ð5.25	Ð5	Ð4.75	V
VL		4.75	5	5.25	4.75	5	5.25	V
Quiescent Currents
I(+VA)10			8	10		8	10	mA
I(ÐVA)10			8	9.5		8	9.5	mA
I(VL)			30	42		30	42	A
Power Dissipation10	PGA in Standby Mode11		77	96		77	96	mW
	PGA in Standby Mode11		56	70		56	70	mW
	In Power-Down Mode11, 12							W
	Reference Input = 3 V		650			650		W
	Reference Input = 0 V		250			250		W

NOTES

1Tested at the output word rate FO = 1 kHz. FO is the AD1556 output word rate, the inverse of the sampling rate. See Tables I, Ia, Ib for other output word rates.

2Tested with a full-scale input signal at approximately 24 Hz. 3This parameter is guaranteed by design.

4Tested at the output word rate FO = 1 kHz with input signals of 30 Hz and 50 Hz, each 6 dB down full scale.

5This specification is for the AD1555 only and does not include the errors from external components as, for instance, the external reference. 6This offset specification is referred to the modulator output.

7Characterized with a 100 mV p-p sine wave applied separately to each supply. 8Contact factory for extended temperature range.

9Recommended Reference: AD780BR.

10Specified with analog inputs grounded.

11See Table III for configuration conditions.

12Specified with MCLK input grounded.

Specifications subject to change without notice.

AD1556–SPECIFICATIONS (VL = 2.85 V to 5.25 V; CLKIN = 1.024 MHz; TA = TMIN to TMAX unless otherwise noted.)

			AD1556AS
Parameter	Notes	Min	Typ	Max	Unit

FILTER PERFORMANCES
Pass-Band Ripple		Ð0.05		+0.05	dB
Stop-Band Attenuation	All Filters Except FO =16 kHz			Ð135	dB
Filters Characteristics	FO =16 kHz		See Table II	Ð86	dB
Filters Characteristics			See Table II

DIGITAL INPUTS OUTPUTS
VIL		Ð0.3		+0.8	V
VIH		+2.0		VL + 0.3	V
IIL		Ð10		+10	A
IIH		Ð10		+10	A
VOL	ISINK = +2 mA			+0.5	V
VOH	ISOURCE = Ð2 mA	VL Ð 0.6			V
POWER SUPPLIES
Specified Performance
VL		2.85		5.25	V
Quiescent Currents
I(VL)			4	5	mA
Power Dissipation	VL = 3.3 V, FO = 1 kHz		6.2	8.5	mW
	In Power-Down Mode		70		W
TEMPERATURE RANGE*					°C
Specified Performance, TMIN to TMAX		Ð55		+85	°C

*Contact factory for extended temperature range.

Specifications subject to change without notice.

REV. B

–3–

AD1555/AD1556

Table I. Dynamic and Noise Typical Performances

Input and Gain

MODIN

PGA = 1 (0 dB)

PGA = 2.5 (8 dB)

PGA = 8.5 (19 dB)

PGA = 34 (31 dB)

PGA = 128 (42 dB)

Input Range

1.6 V rms

636 mV rms

187 mV rms

47 mV rms

12.4 mV rms

Dynamic Range

FO = 16 kHz (1/16 ms)

40 dB

FO = 8 kHz (1/8 ms)

69 dB

FO = 4 kHz (1/4 ms)

98 dB

97 dB

91 dB

FO = 2 kHz (1/2 ms)

117 dB

116.5 dB

114.5 dB

106.5 dB

95 dB

FO = 1 kHz (1 ms)

120 dB

119.5 dB

117.5 dB

109.5 dB

98 dB

FO = 500 Hz (2 ms)

123 dB

122.5 dB

120 dB

112.5 dB

101 dB

FO = 250 Hz (4 ms)

126 dB

125.5 dB

123 dB

115.5 dB

104 dB

Equivalent Input Noise

470 V rms

138 V rms

FO = 16 kHz (1/16 ms)

15.5 mV rms

6.17 mV rms

1.84 mV rms

FO = 8 kHz (1/8 ms)

560 V rms

220 V rms

65.5 V rms

16.4 V rms

4.5 V rms

FO = 4 kHz (1/4 ms)

20 V rms

8 V rms

2.36 V rms

661 nV rms

351 nV rms

FO = 2 kHz (1/2 ms)

2.25 V rms

952 nV rms

353 nV rms

225 nV rms

223 nV rms

FO = 1 kHz (1 ms)

1.59 V rms

674 nV rms

250 nV rms

159 nV rms

FO = 500 Hz (2 ms)

1.13 V rms

477 nV rms

187 nV rms

113 nV rms

111 nV rms

FO = 250 Hz (4 ms)

797 nV rms

338 nV rms

133 nV rms

80 nV rms

79 nV rms

Table Ia. Minimum Dynamic Performances (AD1555AP Only)*

Input and Gain

MODIN

PGA = 1 (0 dB)

PGA = 2.5 (8 dB)

PGA = 8.5 (19 dB)

PGA = 34 (31 dB)

FO = 1 kHz (1 ms)

116

115.5

114

104.5

FO = 500 Hz (2 ms)

119

118.5

117

107.5

FO = 250 Hz (4 ms)

122

121.5

120

110.5

*Not tested in production. Guaranteed by design.

Table Ib. Minimum Dynamic Performances (AD1555BP Only)*

Input and Gain	MODIN	PGA = 1 (0 dB)	PGA = 2.5 (8 dB)	PGA = 8.5 (19 dB)	PGA = 34 (31 dB)

FO = 1 kHz (1 ms)	116.5	116.5	116	114	104.5
FO = 500 Hz (2 ms)	119.5	119.5	119	117	107.5
FO = 250 Hz (4 ms)	122.5	122.5	121	120	110.5

*Not tested in production. Guaranteed by design.

Table II. Filter Characteristics

Output Word Rate FO		Pass Band	–3 dB Frequency	Stop Band	Group Delay
(Sampling Rate in ms)		(Hz)	(Hz)	(Hz)	(ms)

16000 Hz (1/16 ms)		6000	6480	8000	0.984
8000	Hz (1/8 ms)	3000	3267.5	4000	3
4000	Hz (1/4 ms)	1500	1634	2000	6
2000	Hz (1/2 ms)	750	816.9	1000	12
1000	Hz (1 ms)	375	408.5	500	24
500 Hz (2 ms)		187.5	204.2	250	48
250 Hz (4 ms)		93.75	101.4	125	93

–4–

REV. B

AD1555/AD1556

(+VA = +5 V 5%; –VA = –5 V 5%; AD1555 VL = 5 V 5%, AD1556 VL = 2.85 V to 5.25 V;

TIMING SPECIFICATIONS CLKIN = 1.024 MHz; AGND = DGND = 0 V; CL = 50 pF; TA = TMIN to TMAX, unless otherwise noted)

	Symbol	Min	Typ	Max	Unit

CLKIN Frequency1	fCLKIN	0.975	1.024	1.075	MHz
CLKIN Duty Cycle Error		45		55	%
MCLK Output Frequency1			fCLKIN/4
SYNC Setup Time	t1	10			ns
SYNC Hold Time	t2	10			ns
CLKIN Rising to MCLK Output Falling on SYNC	t3			20	ns
CLKIN Falling to MCLK Output Rising	t4			20	ns
CLKIN Falling to MCLK Output Falling	t5			20	ns
MCLK Input Falling to MDATA Falling	t6			30	ns
MCLK Input Rising to MDATA and MFLG Valid	t7			100	ns
TDATA Setup Time after SYNC	t8	5			ns
TDATA Hold Time	t9	5			ns
RESET Setup Time	t10	15			ns
RESET Hold Time	t11	15			ns
CLKIN Falling to DRDY Rising	t12			20	ns
CLKIN Rising to DRDY Falling2	t13			20	ns
CLKIN Rising to ERROR Falling	t14			50	ns
RSEL to Data Valid	t15			25	ns
RSEL Setup to SCLK Falling	t16	10			ns
DRDY to Data Valid	t17			25	ns
DRDY High Setup to SCLK Falling	t18	10			ns
R/W to Data Valid	t19			25	ns
R/W High Setup to SCLK Falling	t20	10			ns
CS to Data Valid	t21			25	ns
CS Low Setup to SCLK Falling	t22	10			ns
SCLK Rising to DOUT Valid	t23			25	ns
SCLK High Pulsewidth	t24	25			ns
SCLK Low Pulsewidth	t25	25			ns
SCLK Period	t26	70			ns
SCLK Falling to DRDY Falling2	t27			20	ns
CS High or R/W Low to DOUT Hi-Z	t28			20	ns
R/W Low Setup to SCLK Falling	t29	10			ns
CS Low Setup to SCLK Falling	t30	10			ns
Data Setup Time to SCLK Falling	t31	10			ns
Data Hold Time after SCLK Falling	t32	10			ns
R/W Hold Time after SCLK Falling	t33	10			ns

NOTES

1The gain of the modulator is proportional to fCLKIN and MCLK frequency.

2With DRDYBUF low only. When DRDYBUF is high, this timing also depends on the value of the external pull-down resistor.

Specifications subject to change without notice.

	1.6mA	IOL
TO OUTPUT		1.4V
PIN	CL	1.4V
PIN

	50pF
	500 A	IOH

Figure 2. Load Circuit for Digital Interface Timing

REV. B

–5–

AD1555/AD1556

CLKIN

t2
t1
SYNC
t3	t4	t5
	t4

MCLK
(FS)
MDATA	DATA VALID	DATA VALID
	t6	t7
		t7
t8	t9
TDATA	VALID	VALID
Figure 3. AD1555/AD1556 Interface Timing
t11
t10
RESET
	t2
	t1
CLKIN
SYNC
	t12	t13
	t12	t12
DRDY
		t14
ERROR
Figure 4. AD1556 RESET, DRDY, and Overwrite Timings

–6–

REV. B

t15

RSEL

t16

t17

DRDY

t18

t19

R/W

t20

t21

t22

DOUT

MSB

SCLK

CS
CS

	t29
	t29

R/W

	t30
	t30
SCLK

			t32
	t31


DIN		MSB

t27

MSB–1

LSB+1

LSB

t23

t26

t24

t25

Figure 5. Serial Read Timing

	t24
t26	t25
MSB–1	LSB+1

Figure 6. Serial Write Timing

AD1555/AD1556

t28

HI-Z

t33

LSB

REV. B

–7–

AD1555/AD1556

ABSOLUTE MAXIMUM RATINGS1
Analog Inputs
Pins 7, 8, 23, 24, 25, 28 . . . . . .	ÐVA Ð 0.3 V to +VA + 0.3 V
AIN(+), AIN(Ð) DC Input Current . . .		. . . .	. . . . ±100 mA
AIN(+), AIN(Ð) 2 s Pulse Input Current . .			. . . . . . ±1.5 A
Supply Voltages
+VA to ÐVA . . . . . . . . . . . . . . . . .	. . . . .	. . .	Ð0.3 V to +14 V
+VA to AGND . . . . . . . . . . . . . .	. . . . . .	. . .	Ð0.3 V to +7 V
ÐVA to AGND . . . . . . . . . . . . . .	. . . . . .	. . .	Ð7 V to +0.3 V
VL to DGND . . . . . . . . . . . . . . .	. . . . . .	. . .	Ð0.3 V to +7 V
Ground Voltage Differences			±0.3 V
DGND, AGND1, AGND2, AGND3 . .		. . .	±0.3 V
Digital Inputs . . . . . . . . . . . . . . . .	. . . .	Ð0.3 V to VL + 0.3 V
Internal Power Dissipation2
AD1555 . . . . . . . . . . . . . . . . . . .	. . . . . .	. . .	. . . . . . . 1.8 W
AD1556 . . . . . . . . . . . . . . . . . . .	. . . . . .	. . .	. . . . . . . 1.8 W

Junction Temperature . . . . . . . . . . . . . . . . .	. . . . . . . . 150°C
Storage Temperature . . . . . . . . . . . . . . . . . .	Ð65°C to +150°C
Lead Temperature Range	300°C
(Soldering 10 sec) . . . . . . . . . . . . . . . . . . .	300°C

NOTES

1Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

2Specification is for device in free air:

28-lead PLCC: θJA = 36°C/W, θJC = 20°C/W

44-lead MQFP: θJA = 36°C/W, θJC = 14°C/W

ORDERING GUIDE

	Temperature	Package	Package
Model	Range*	Description	Option

AD1555AP	0°C to 85°C	Plastic Lead Chip Carrier	P-28A
AD1555APRL	0°C to 85°C	Plastic Lead Chip Carrier	P-28A
AD1555BP	Ð55°C to +85 °C	Plastic Lead Chip Carrier	P-28A
AD1555BPRL	Ð55°C to +85 °C	Plastic Lead Chip Carrier	P-28A
AD1556AS	Ð55°C to +85 °C	Plastic Quad Flatpack	S-44A
AD1556ASRL	Ð55°C to +85 °C	Plastic Quad Flatpack	S-44A
EVAL-AD1555/AD1556EB			Evaluation Board
AD1555/56-REF			Reference Design

*Contact factory for extended temperature range.

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD1555/AD1556 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

WARNING!

ESD SENSITIVE DEVICE

–8–

REV. B

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