WOLFSON WM5621L

WM5621L
Production Data
Jan. 1997 Rev. 1.0
Low-power Quadruple 8-Bit DAC
Description
Features
WM5621L is a quadruple 8-bit digital to analogue converter
(DAC) with buffered reference inputs (high impedance). The
DAC produces an output voltage that ranges between
either one or two times the reference voltage and GND. The
DAC is monotonic. The device operates from a single
supply in the range 2.7V to 5.5V. A power-on reset function
is incorporated to provide repeatable start-up conditions. A
global hardware shut-down terminal and the capacity to
shut-down each individual DAC with software are provided
to minimize power consumption.
WM5621L interfaces to all popular microcontrollers and
microprocessors via a three wire serial interface with CMOS
compatible, schmitt trigger, digital inputs. Alternatively a two
wire serial interface can be activated. An 11-bit command
word consists of eight bits of data, two DAC select bits and
a range bit for selection between the times one or times two
output range. The DACregisters are double buffered which
allows a complete set of new values to be written to the
device, and then under control of HWACT, all of the DAC
outputs are simultaneously updated.
Ideal in space critical applications WM5621L is available
in small outline and DIP packages and is characterized for
operation from -25oC to 85oC.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Individual (or all) DAC's can be powered-down
One low-power 8-bit voltage output DAC
Three 8-bit voltage output DACs
Fast serial interface (1 MHz max)
Simple 2 or 3 wire interface
Programmable for 1 or 2 times output range
High impedance reference inputs for each DAC
Simultaneous update facility
Extended temperature range (-25oC to 85 oC)
Single supply operation, range 2.7 V to 5.5 V
0 to 4 V output (x2 output range) at 5 V VDD
0 to 2.5 V output (x2 output range) at 3 V VDD
Low power specification:
All DACs on
: 3.6 mW at 3.6 V typ
: 6 mW at 5 V typ
Low power DAC
: 0.54 mW at 3.6V typ
All DAC's shutdown
: 0.18 mW at 3.6V typ
Guaranteed monotonic output
Applications
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Mobile Communications
Programmable d.c. voltage sources
Digitally controlled attenuator/amplifier
Signal synthesis
Automatic test equipment
Block Diagram
Production Data data sheets contain final
specifications current on publication date. Supply
of products conforms to Wolfson Microelectronics
standard terms and conditions
Wolfson Microelectronics
Lutton Court, Bernard Terrace, Edinburgh EH8 9NX, UK
Tel: +44 (0) 131 667 9386
Fax: +44 (0) 131 667 5176
email: [email protected]
www: http://www.wolfson.co.uk
© 1996 Wolfson Microelectronics
WM5621L
Pin Configuration
Ordering Information
Top View
N or D Packages
GND
REF A
REF B
REF C
REF D
1
14
2
13
3
12
4
11
5
10
DATA
CLK
6
9
7
8
DEVICE
WM5621LED
WM5621LEN
VDD
HWACT
DACA
DACB
DACC
DACD
EN
Absolute Maximum Ratings (note 1)
Supply Voltage (VDD - GND) . . . . . . . . . . . +7V
Digital Inputs . . . . . . . . . GND - 0.3 V, VDD + 0.3 V
Reference inputs . . . . . . . GND - 0.3 V, VDD + 0.3 V
TEMP. RANGE
-25oC to 85oC
-25oC to 85oC
PACKAGE
14 pin plastic SO
14 pin DIP
o
o
Operating temperature range, TA . . . . . -25 C to +85 C
Storage Temperature . . . . . . . . . -50oC to +150 ooC
Lead Temperature (soldering, 10 sec) . . . . . +260 C
Recommended Operating Conditions
MIN
2.7
GND
10
0.8 VDD
Supply Voltage
Reference input range
DAC output load resistance to GND
High level digital input voltage
Low level digital input voltage
Clock frequency
Operating free-air temperature, TA
5
NOMINAL
3.3
MAX
5.5
VDD - 1.5
0.2 VDD
1
85
-25
UNIT
V
V
kΩ
V
V
MHz
O
C
Electrical Characteristics
VDD = 3 V to 3.6V, GND = 0 V, VREF = 1.25 V, RL = 10 kΩ, CL = 100 pF, x1 gain output range, TA = full range
unless otherwise stated.
PARAMETER
Supply Voltage
High level digital input voltage
Low level digital input voltage
Reference voltage, VREF [A|B|C|D]
Load resistance
Data input setup time
Data input hold time
CLK ↓ to EN ↓
EN ↑ to CLK ↓
CLK period high
EN low time
Clock frequency
Operating free-air temperature
SYMBOL
CONDITIONS
VDD
see note 2
VIH
VIL
x1 gain
RL
tSD
tHD
tEN
tLC
cph
tenl
fCLK
TA
see note 3
see note 3
see note 3
MIN
2.7
0.8 VDD
GND
10
50
50
MAX
5.5
0.2 VDD
VDD-1.5
100
100
400
200
-25
Wolfson Microelectronics
2
NOM
3.3
1.0
85
UNIT
V
V
V
V
kΩ
ns
ns
ns
ns
ns
ns
MHz
O
C
WM5621L
Electrical Characteristics (continued)
VDD = 3 V to 3.6V, GND = 0 V, VREF = 1.25 V, RL = 10 kΩ, CL = 100 pF, x1 gain output range, TA = full range
unless otherwise stated.
PARAMETER
Max. full-scale output voltage
SYMBOL
Vomax
High level input current
Low level input current
Output sink current DACA
Output sink current DACB
Output Source Current
IIH
IIL
Io (sink)
Io (sink)
Io (source)
Input capacitance
Reference input capacitance
Supply current
CI
CONDITIONS
Vref=1.5V, open cct. output
,x2 gain
VI = VDD
VI = 0V
at DAC code 0
at DAC code 0
Each DAC output, at DAC
code 255
MIN
VDD-100
MAX UNIT
mV
± 10
± 10
5
20
1
µA
µA
µA
µA
mA
IDAC
A, B, C, D inputs
VDD = 3.6V
VDD = 5.0V
VDD = 3.6V (Note 4)
15
15
1
1
150
1.5
1.5
250
pF
pF
mA
mA
µA
50
100
µA
± 10
± 1.0
µA
LSB
± 0.9
LSB
30
mV
IDD
Supply current One low
power DAC Active
Supply Current ALL DACs
Shutdown
Reference input current
Integral Nonlinearity
Iddsd
VDD = 3.6V (see note 4)
IREF
INL
Differential Nonlinearity
DNL
Zero scale error
ZCE
A, B, C, D inputs
VREF = 1.25V, Range x2.
(note 5,13)
VREF = 1.25V, Range x2.
(note 6,13)
VREF = 1.25V,Range x2.
0
(note 7)
VREF = 1.25V,Input code = 00
Hex (note 8)
Zero scale error temperature
coefficient
Zero scale error supply
rejection
Full scale error
Full scale error temperature
coefficient
Full scale error supply
rejection
Feedback resistor network
TYP
2
FSE
Range x 2. (note 9)
VREF = 1.25V,Range x2.
(note 10)
± 0.1
10
µV/ OC
2
mV/V
± 60
mV
± 25
µV/ C
2
mV/V
168
kΩ
O
resistance
Notes:
1. Absolute Maximum Ratings are stress ratings only.
Permanent damage to the device may be caused by
continuously operating at or beyond these limits. Device functional operating range limits are given under
Recommended Operating Conditions. Guaranteed
performance specifications are given under Electrical
Characteristics at the test conditions specified.
2. The device operates over the supply voltage range of
2.7V to 5.5V. Over this voltage range the device responds correctly to data input by changing the voltage
output but conversion accuracy is not specified over
this extended range.
Wolfson Microelectronics
3
WM5621L
Electrical Characteristics
VDD = 3 V to 3.6V, GND = 0 V, VREF = 1.25 V, RL = 10 kΩ, C L = 100 pF, x1 gain output range, TA = full range
unless otherwise stated.
PARAMETER
Output slew rate rising DACA
SYMBOL
CONDITIONS
MIN
Output slew rate falling DACA
Output slew rate DACB,C,D
Output settling time rising
DACA
Output settling time falling
DACA
Output settling time rising
DACB,C,D
Output settling time falling
DACB,C,D
Output settling time HWACT
or ACT↑ to output volts DACA
(note 14)
Output settling time HWACT
or ACT↑ to output volts
DACB,C,D (note 14)
Large signal Bandwidth
Digital crosstalk
5
Reference feedthrough
Channel-to-channel isolation
Channel-to-channel isolation
when in shutdown
Reference bandwidth DACA
Reference bandwidth
DACB,C,D
MAX UNIT
V/µS
0.5
V/µS
1
To 1/2 LSB, VDD=3V
20
V/µS
µS
To 1/2 LSB, VDD=3V
75
µS
To 1/2 LSB, VDD=3V
10
µS
To 1/2 LSB, VDD=3V
75
µS
To 1/2 LSB, VDD=3V
40
120*
µS
To 1/2 LSB, VDD=3V
25
75*
µS
Measured at -3dB point
CLK=1MHz sq. wave
measured at DACA-DACD
A,B,C,D inputs (note 15)
A,B,C,D inputs (note 16)
A,B,C,D inputs
100
-50
KHz
dB
-60
-60
-40
dB
dB
dB
note 17
note 17
20
100
kHz
kHz
Notes:
3. This is tested by design but is not production tested.
4. This is measured with no load (open circuit output),
Vref = 1.25V, range = x2.
5. Integral Nonlinearity (INL) is the maximum deviation of
the output from the line between zero and full scale (excluding the effects of zero code and full-scale errors).
6. Differential Nonlinearity (DNL) is the difference between the measured and ideal 1 LSB amplitude
change of any two adjacent codes. A guarantee of
monotonicity means the output voltage changes in the
same direction (or remains constant) as a change in
the digital input code.
7.
Zero-scale error is the deviation from zero voltage
output when the digital input code is zero.
8. Zero scale error temperature coefficient is given by:
ZCETC = (ZCE(Tmax ) - ZCE(T min))/V REF x 10 6 /
(Tmax - Tmin)
9. Full-Scale error is the deviation from the ideal full-scale
output (Vref - 1LSB) with an output load of 10kΩ.
10. Full-Scale Temperature Coefficient is given by:
6
FSETC = (FSE(Tmax) - FSE(T min ))/VREF x 10 /
(Tmax - Tmin)
11. Zero-code Error Rejection Ratio (ZCE-RR) is
measured by varying the VDD voltage, from 4.75 to
5.25 V d.c., and measuring the proportion of this
signal imposed on the zero-code output voltage.
Wolfson Microelectronics
4
TYP
0.8
WM5621L
Electrical Characteristics (continued)
12. Full Scale Error Rejection Ratio (FSE-RR) is
measured by varying the VDD voltage, from 4.75 to
5.25 V d.c., and measuring the proportion of this
signal imposed on the full-scale output voltage.
13. Linearity is only specified for DAC codes 1 through
255.
14. The ACT bit is latched on falling edge of EN.
15. Reference feedthrough is measured at any DAC output with an input code = 00 hex with a Vref input = 1Vdc
+ 1 Vpp at 10kHz.
16. Channel-to-channel isolation is measured by setting
the input code of one DAC to FF hex and the code of
all other DACs to 00 hex with Vref input = 1Vdc + 1
Vpp at 10kHz.
17. Reference bandwidth is the -3dB bandwidth with an
ideal input at Vref = 1.25 Vdc + 2 Vpp and with a digital input code of full-scale (range set to x1 and Vdd =
5V)
Typical Performance Characteristics
Typical DNL, INL and TUE at VDD = 5 V
Differential Nonlinearity
Vd d = 5 .0 V, Vre f = 2 .5 V , R ang e = x1 @
2 5' C
Integral Nonlinearity
Vdd = 5 .0V, Vre f = 2. 5V, Ra ng e = x1 @ 25 'C
o
VDD = 5.0, VREF = 2.5V, Range = x1 at 25 C
0.2
0.15
0.15
Error (LSBs)
Error (LSBs)
Err o r (lsb s)
Error (lsbs)
0.05
0
-0.05
-0.1
-0.15
0.05
0
-0.05
-0.1
-0.15
-0.2
-0.2
0
32
64
96
128
160
192
224
256
0
32
64
Co de
96
128
160
192
224
256
224
256
Co d e
Input Code
Input Code
Differential Nonlinearity
Total Unadjusted Error
o
Total Unad justed Er ror
VDD = 5.0, VREF = 2.5V,
Range = x1 at 25 C
Vdd = 5.0 V, Vref = 2.5 V, Rang e = x 1 @ 25 'C
o
Li neari ty
V DD = 5.0, VREF = Differenti
2.0V,al Non
Range
= x2 at 25 C
Vdd = 5 .0V, Vre f = 2 .0V, Ran ge = x2 @ 25 'C
0.2
0.15
0.15
Error (LSBs)
0.2
0.1
Error (lsbs)
0.05
Error (lsbs)
o
0.1
0.1
Error (LSBs)
I ntegral Non Li neari ty
V DD = 5.0, VREF = 2.5V, Range = x1 at 25 C
0.2
0
-0.05
0.1
0.05
0
-0.05
-0.1
-0.1
-0.15
-0.15
-0.2
-0.2
0
32
64
96
128
160
192
224
256
0
32
Cod e
64
96
128
160
192
Co d e
Input Code
Input Code
Wolfson Microelectronics
5
WM5621L
Typical Performance Characteristics
(continued)
Integral Nonlinearity
Vdd = 5 .0V, Vre f = 2 .0V, Ran ge = x2 @ 25'C
Total Unadjusted Error
o
In teg ral Non Lin earity
o
To tal Un adju ste d E rror
Vdd = 5 .0V, Vre f = 2 .0V, Ran ge = x2 @ 25 'C
VDD = 5.0, VREF = 2.0V, Range = x2 at 25 C
0.2
0.2
0.15
0.15
0.1
0.1
0.05
0.05
Error (lsbs)
Error (LSBs)
Error (lsbs)
Error (LSBs)
VDD = 5.0, VREF = 2.0V, Range = x2 at 25 C
0
-0.05
-0.1
-0.15
-0.2
0
-0.05
-0.1
-0.15
-0.2
0
32
64
96
128
160
192
224
256
0
32
64
Co de
96
128
160
192
224
256
224
256
Input Code
Co d e
Input Code
Typical DNL, INL and TUE at VDD = 3 V
Differential Nonlinearity
Vdd = 3.0 V, Vref = 1.2 5V, Ran ge = x2 @ 25'C
0.2
Differen tial Non Lin earity
Integral Nonlinearity
Vdd = 3.0V, Vref = 1.25V, Range =x2 @ 25'C
o
V DD = 3.0, V REF = 1.25V, Range = x2 at 25 C
0.2
o
0.15
0.1
0.05
0.05
0
-0.05
-0.1
Error (lsbs)
0.1
Error (LSBs)
Error (lsbs)
Error (LSBs)
0.15
I ntegral Non Li neari ty
VDD = 3.0, VREF = 1.25V, Range = x2 at 25 C
-0.15
0
-0.05
-0.1
-0.15
-0.2
-0.2
0
32
64
96
128
160
192
224
256
0
32
64
Cod e
96
128
160
192
Code
Input Code
Input Code
Total Unadjusted Error
Vdd = 3. 0V, Vre f = 1. 25 V, Ra ng e = x 2 @ 25 'C
o
To tal Un adju sted E rror
V DD = 3.0, VREF = 1.25V, Range = x2 at 25 C
0.2
Error (LSBs)
0.15
Error (lsbs)
5
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
0
32
64
96
128
160
192
224
256
Co d e
Input Code
Supply Current v Temperature
Output Source Current vs Output Voltage
Supply Current vs Temperature
o
VDD = 5.0, VREF = 2V, Range = 2x, Input Code = 255, Temperature = 25 C
1.15
8
Vdd = 5V, Vref = 2.0V, Range = 2x
Input Code = 255, Temperature = 25'C
1.1
6
1.05
5
1
IDD (mA)
IDD (mA)
Iout (mA)
IOUT (mA)
7
4
3
2
Vdd
5V,5.0,
VrefV
=REF
2.0V= 2V,
V DD= =
Range = 2x, Input Code = 255
Range = 2x, Input Code = 255
0.95
0.9
Vdd V
= REF
3V, Vref
= 1.25V
VDD =3.0,
= 1.25V,
2x, Input Code =
Range Range
= 2x, =Input
Code = 255
255
0.85
1
0.8
0
0
1
2
3
4
5
-30
-15
Wolfson Microelectronics
6
0
15
30
45
Tem p erature ('C)
Temperature
(oC)
Vo ut (V)
V OUT
(V)
60
75
90
WM5621L
Typical Performance Characteristics (continued)
Large Signal Frequency Response
Small Signal Frequency Response
La rge Signal Fre que ncy Re sponse
Sm all Signa l Fre que nc y Re spons e
5
-10
-15
Vdd
= 5V,= Vref
= 1.25V
pp
VDD
5.0,
VREF+ 2V
= 1.25V
+ 2Vpp,
Range = 1x, Input Code = 255
Range == 1x,
Temperature
25'CInputo Code = 255
Temperature = 25 C
-20
-25
1000
10000
100000
Frequency (KHz)
Frequency
(KHz)
1000000
Relative Gain (dB)
Relative Gain (dB)
Relative
Gain
(dB)
Relative
Gain (dB)
0
-5
5
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
V
DD= =
Vdd
5V,5V,
VrefV=REF
2V +=1V2V
pp + 1Vpp,
Range = 1x,
InputInput
Code Code
= 255 = 255
Range
= 1x,
o
Temperature = 25'C
Temperature
= 25 C
1
10
100
Frequency (KHz)
Frequency
(KHz)
1000
10000
Wolfson Microelectronics
7
WM5621L
Input and Output Circuits
Pin Descriptions
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
5
Name
GND
REFA
REFB
REFC
REFD
DATA
CLK
EN
DACD
DACC
DACB
DACA
HWACT
VDD
Type
Supply
Analogue input
Analogue input
Analogue input
Analogue input
Digital input
Digital input
Digital input
Analogue output
Analogue output
Analogue output
Analogue output
Digital input
Supply
Function
Ground return and reference terminal
Reference voltage input to DACA
Reference voltage input to DACB
Reference voltage input to DACC
Reference voltage input to DACD
Serial interface data
Serial interface clock, negative edge sensitive
Input Enable
DAC D output
DAC C output
DAC B output
DAC A output
Hardware activate
Positive supply voltage
Timing Waveforms
Figure 1: Detailed timing of serial interface
Wolfson Microelectronics
8
Figure 4: In single buffered mode, synchronisation can be regained by clocking in at least 12 ZEROs. Registers are updated on the twelfth
falling edge of CLK after a Start Bit has been detected.
Figure 3: Multiple DAC updates at the same time are possible by holding EN high over multiple serial words. All DACs are updated on the
falling edge of EN.
Figure 2: Serial write in double buffered mode. Registers are latched on falling edge of EN. Preceding ZEROs on DATA are ignored.
WM5621L
Wolfson Microelectronics
9
WM5621L
Functional Description
DAC operation
Each of WM5621L's four digital to analogue converters
(DACs) are implemented using a single resistor string with
256 taps corresponding to each of the input 8-bit codes.
One end of a resistor string is connected to the GND pin
and the other end is driven from the output of a reference
input buffer. The use of a resistor string guarantees
monotonicity of the DAC's output voltage. Linearity depends
upon the matching of the resistor string's individual elements
and the performance of the output buffer. The reference input
buffers present a high impedance to reference sources.
Double Buffered Mode
In normal operation the EN signal is used to control the
latching of data. All DAC registers and all bits of the
control word (other than MODE) are double buffered, with
the second buffer only being enabled when the EN pin is
taken low. In this way it is possible to update any number
of DAC inputs at once by writing a 12-bit word to update
each DAC register, with EN held high for all writes. When
EN is pulled low at the end of the last write, all DAC inputs
are latched at the same time. Figure 3 shows DACs A
and B being written to in this way.
Each DAC has a voltage output amplifier which is
programmable for gains of x1 or x2 through the serial
interface. The DAC output amplifiers feature rail to rail
output stages, allowing outputs over the full supply voltage
range to be achieved with a x2 gain setting and a VDD/2
reference voltage input. Used in this way a slight
degradation in linearity will occur as the output voltage
approaches VDD.
This mode also allows multiple devices to be share DATA
and CLK lines by having only separate EN lines.
Control of the WM5621L is effected through a serial
interface using three dedicated pins, CLK, DATA and EN.
A fourth pin (HWACT) is used to control the power-down
controls to each of the 4 DACs.
Serial Interface
5
The serial interface uses the CLK pin to clock in data words
presented serially on the DATA pin. The data words are
12 bits long and are written to either a control register or
to one of the four DAC registers. When the EN pin is held
low the serial interface is held in reset.
Figure 1 shows the format of the 12-bit data word transfer
into the WM5621L. DATA is clocked on the falling edge of
CLK. Every data word must start with a high start bit
(preceeding zeros are ignored). The second bit is the
register select bit which selects a write into either the
control register or one of the DAC registers. Table 1 shows
all valid write sequences.
Single Buffered Mode
If the device is to be operated in single buffered mode, the
EN pin should be tied high, and the interface is always
active. The first write to the device after power-on should
be a write to the control register to set the MODE bit high.
The double buffered action is not possible as all words
are latched across on the twelfth falling edge of CLK.
Loss of synchronisation may occur if glitches are present
on the CLK and DATA inputs, a condition which may
occur at power-on. If this has happened it is possible to
regain synchronisation by clocking in at least 12 zeros
(see Figure 4).
It is not possible to reset the MODE bit from 1 to 0.
Operation of the device after any attempt to do this is
undefined.
DAC Registers
Each DAC register holds an 8-bit unsigned byte to
represent the DAC code. Table 1 indicates how these
bytes are clocked into the DAC registers, with D7 being
the most significant bit of the byte. These registers are
reset to 0 at power-on.
The serial interface can operate in one of two ways,
controlled by the setting of the MODE bit in the control
register. The MODE bit defaults to 0 on power up which sets
the device to work in a double buffered mode. When MODE
is set to 1, the device operates in a single buffered mode,
which can be controlled through only two pins (DATA and
CLK, EN held high).
Wolfson Microelectronics
10
WM5621L
Functional Description (continued)
Bit
Control
Word
Start Bit 1
Register 0
Select
3
MODE
4
RNGA
5
RNGB
6
RNGC
7
RNGD
8
SIA
9
SIB
10
SIC
11
SID
12
ACT
DACA
Write
1
1
DACB
Write
1
1
0
0
D7
D6
D5
D4
D3
D2
D1
D0
0
1
D7
D6
D5
D4
D3
D2
D1
D0
DACC
Write
1
1
1
0
D7
D6
D5
D4
D3
D2
D1
D0
DACD
Write
1
1
1
1
D7
D6
D5
D4
D3
D2
D1
D0
Table 1
SIA
0
0
0
0
1
1
1
1
Bit
Power-up state
Function
MODE
0
Control serial interface
RNG A
1
DACA range select
(0 = x1, 1 = x2)
RNG B
1
DACB range select
(0 = x1, 1 = x2)
RNG C
1
DACC range select
(0 = x1, 1 = x2)
RNG D
1
DACD range select
(0 = x1, 1 = x2)
SIA
0
DACA shutdown inhibit
SIB
0
DACB shutdown inhibit
SIC
0
DACC shutdown inhibit
SID
0
DACD shutdown inhibit
ACT
0
Software shutdown control
Table 2
ACT
0
0
1
1
0
0
1
1
HWACT
0
1
0
1
0
1
0
1
DAC status
shutdown
shutdown
shutdown
active
active
active
active
active
Linearity, offset, and gain error using
single end supplies
When an amplifier is operated from a single supply, the
voltage offset can still be either positive or negative. With
a positive offset, the output voltage changes on the first
code change. With a negative offset the output voltage
may not change with the first code depending on the
magnitude of the offset voltage.
Table 3
Control Register
The control register contains 10 active bits. The MODE bit
controls the operation of the serial interface as described
above. The function of the control register bits, and their
state on power-up, are shown in table 2.
The shutdown state of each DAC is controlled through the
shutdown inhibit bit for that channel (SIx), the ACT bit of the
control register, and the HWACT pin. Table 3 shows the
logical action of these three controlling bits for DAC A. It is
possible, for example, to have any combination of DACs
switched from shutdown to active by the HWACT pin, while
the remaining DACs are held always active (achieve this by
setting ACT=1, SIx=0 for the switching DACs, and SIx=1 for
the always active DACs).
The output amplifier, with a negative voltage offset,
attempts to drive the output to a negative voltage.
However, because the most negative supply rail is GND,
the output cannot drive to a negative voltage.
So when the output offset voltage is negative, the output
voltage remains at ZERO volts until the input code value
produces a sufficient output voltage to overcome the
inherent negative offset voltage, resulting in the transfer
function shown in Figure 5.
This negative offset error, not the linearity error, produces
this breakpoint. The transfer function would have followed
the dotted line if the output buffer could drive to a negative
voltage.
Wolfson Microelectronics
11
WM5621L
Functional Description (continued)
For a DAC, linearity is measured between ZERO input code
( all inputs 0 ) and full scale code ( all inputs 1 ) after offset
and full scale are adjusted out or accounted for in some
way. However, single supply operation does not allow for
adjustment when the offset is negative due to the breakpoint in the transfer function. So the linearity in the unipolar
mode is measured between full scale code and the lowest
code which produces a positive output voltage. The code
is calculated from the maximum specification for the
negative offset.
Figure 5: Effect of negative offset (single supply)
5
Wolfson Microelectronics
12
WM5621L
Package Descriptions
Plastic Small-Outline Package
D - 8 pins shown
4.00
3.80
A
8
5
1
4
6.20
5.80
1.75
0.50
1.35
0.25
x 45O NOM
0.25
0.19
0.51
0.33
0.25
Pin spacing
1.27 B.S.C.
0.10
0O to 8O
1.27
0.40
Dimension 'A' Variations
N
Min
Max
8
4.80
5.00
14
8.55
8.75
16
9.80
10.00
Notes:
A. Dimensions in millimeters.
B. Complies with Jedec standard MS-012.
C. This drawing is subject to change without notice.
D. Body dimensions do not include mold flash or protrusion.
E. Dimension A, mould flash or protrusion shall not exceed 0.15mm. Body width, interlead flash or protrusions shall
not exceed 0.25mm.
Rev. 1 November 96
Wolfson Microelectronics
13
WM5621L
Package Descriptions
Dual-In-Line Package
N or P
N
1
0.325
N/2
0.290
0.015
Min.
0.280
A
0.070 Max.
0.240
0.210 Max.
Seating
plane
105O
90O
0.014
0.150
0.008
0.115
0.045
0.030
0.022
0.005
Min.
Dimension 'A' Variations
N
5
Min
Pin spacing
0.100 B.S.C.
0.014
Max
8
0.355
0.400
14
16
0.735
0.735
0.775
0.775
20
0.940
0.975
Notes:
A. Dimensions are in inches
B. Falls within JEDEC MS-001( 20 pin package is shorter than MS-001)
C. N is the maximum number of terminals
D. All end pins are partial width pins as shown, except the 14 pin package which is full width.
Rev. 1 November 96
Wolfson Microelectronics
14