Data Sheet AS1500/1/2/3
AS150x – SPECIFICATIONS
(VDD = 3V±10% or 5V±10%, VA = VDD, VB = 0V,
–40°C≤TA≤+125°C unless otherwise noted.)
CK
SD
1
0
1
0
1
0
A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
ELECTRICAL CHARACTERISTICS–ALL
VERSIONS
Sym-
Typ
Conditions Min
21
Max Unit
bol
SWITCHING CHARACTERISTICS
22, 23
Input Clock
Clock Level
t
CH
, t
CL
50
ns
Pulsewidth
High or Low
Data Setup Time
t
DS
5
ns
Data Hold Time
t
DH
5
ns
CSN Setup Time
t
CSS
10
ns
CSN High
10
ns
t
CSW
Pulsewidth
CK Fall to CSN Rise
t
CSH
0
ns
Hold Time
CSN Rise to Clock
10
ns
t
CS1
Rise Setup
Parameter
Table 5: Switching Characteristics
DAC Register
CS
VD
V
O UT
0V
Figure 2: Timing Diagram
SDI
1
0
1
0
1
0
A
X
or
t
C
A
X
or
t
D
t
D
t
CS
t
CL
CK
t
CS
CSN
t
CS
t
CS
t
S
±1%
±1% Error
V
O UT
0V
V
DD
Detailed Description
Serial-Programming
Programming of the AS150x is done via the 3 wire serial
interface. The three input signals are serial data input
(SDI), clock(CK) and chip select (CS). A programming
sequence consists of 10-bit, where the last eight bit
contain the code word for the resistor value. The first two
bits A1 and A0 have to be low(see Table ). The data is
shifted into the internal 10 Bit register with the rising edge
of the CK signal. With the rising edge of the CSN signal
the data becomes valid and the resistance is updated (see
figure 2). A detailed block diagram is shown in figure 3.
A1 A0 D7
0
0 MSB
D6
D5
D4
D3
Data
D2
D1
D0
LSB
Figure 3: Detailed Timing Diagram
Rheostat Operation
The digital potentiometer family AS150x offers nominal
resistor values of 10kΩ, 20 kΩ, 50kΩ and 100kΩ. The
resistor has 256 contact points where the wiper can access
the resistor. The 8-bit code word determines the position
of the wiper and is decoded through an internal logic. The
lowest code 00h is related to the terminal B. The
resistance is then only determined by the wiper resistance
(100Ω). The resistance for the next code 01h is the
nominal resistor RAB (10kΩ, 20 kΩ, 50kΩ or 100kΩ)
divided through 256 plus the wiper resistor. In case of
AS1501 (10kΩ) the total resistance is 39Ω+100Ω=139Ω.
Accordingly the resistor for code 02h is 78Ω+100Ω=178Ω.
The last code 255h does not connect to terminal A directly
(see Figure 5). So the maximum value is 10000Ω - 39Ω
+100Ω = 10061Ω. The general formula for the calculation
of the resistance R
WB
is:
R
WB
(Dx)= (Dx)/256⋅R
AB
+ R
W
Table 6: Serial data format (16 bits)
21
22
23
Typicals represent average readings at 25°C and VDD=5V.
Guaranteed by design and not subject to production test.
Resistor-terminal capacitance tests are measured with 2.5V
bias on the measured terminal. The remaining resistor
terminals are left open circuit.
See timing diagram for location of measured values. All input
control voltages are specified with t
R
= t
F
= 1ns (10% to 90% of
VDD) and timed from a voltage level of 1.6V. Switching
characteristics are measured using VDD=3V or 5V. To avoid
false clocking, a minimum input logic slew rate of 1V/µs should
be maintained.
where R
AB
is the nominal resistance between terminal A
and B, R
W
is the wiper resistance and D
X
is the 8-Bit Code
word. In Table 7 the resistor values between the wiper and
terminal B for AS1501 are given for specific codes D
X
. In
the zero-scale condition the wiper resistance of 100Ω
remains present.
Revision 1.0, Oct 2004
Page 5 of 8
AMSCO [ AUSTRIAMICROSYSTEMS AG ]
