Data Sheet AS1500/1/2/3
AS150x – SPECIFICATIONS
1
A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
DAC Register
SD
CK
(VDD = 3V±10% or 5V±10%, VA = VDD, VB = 0V,
0
1
–40°C≤TA≤+125°C unless otherwise noted.)
0
1
0
ELECTRICAL CHARACTERISTICS–ALL
VERSIONS
CS
VD
0V
VOUT
Sym-
bol
Typ
Parameter
Conditions Min
Max Unit
21
Figure 2: Timing Diagram
22, 23
SWITCHING CHARACTERISTICS
Input Clock
Clock Level
1
tCH, tCL
50
ns
SDI
Pulsewidth
High or Low
tD
Data Setup Time
Data Hold Time
CSN Setup Time
CSN High
tDS
tDH
5
5
ns
ns
ns
tD
tC
tCSS
10
tCS
1
CK
tCSW
tCSH
tCS1
10
ns
ns
ns
Pulsewidth
tCL
CK Fall to CSN Rise
Hold Time
tCS
1
tCS
0
CSN
tCS
tS
CSN Rise to Clock
10
Rise Setup
VDD
VOUT
0V
±1%
Table 5: Switching Characteristics
±1% Error
Figure 3: Detailed Timing Diagram
Detailed Description
Rheostat Operation
The digital potentiometer family AS150x offers nominal
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.
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 RWB is:
A1 A0 D7
MSB
D6
D5
D4
Data
D3
D2
D1
D0
LSB
0
0
Table 6: Serial data format (16 bits)
RWB (Dx)= (Dx)/256⋅RAB + RW
21
Typicals represent average readings at 25°C and VDD=5V.
22
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.
where RAB is the nominal resistance between terminal A
and B, RW is the wiper resistance and DX 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 DX. In
the zero-scale condition the wiper resistance of 100Ω
remains present.
23
See timing diagram for location of measured values. All input
control voltages are specified with tR = tF = 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.
Revision 1.0, Oct 2004
Page 5 of 8
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