
CAT525
5
Doc. No. 2001, Rev. A
PIN DESCRIPTION
Pin
Name
Function
1
2
3
4
5
6
7
8
9
V
REFH2
V
REFH1
V
DD
CLK
RDY/
BSY
CS
DI
DO
PROG
Maximum DPP 2 output voltage
Maximum DPP 1 output voltage
Power supply positive
Clock input pin
Ready/Busy output
Chip select
Serial data input pin
Serial data output pin
Non-volatile Memory Programming
Enable Input
Power supply ground
Minimum DPP 1 output voltage
Minimum DPP 2 output voltage
Minimum DPP 3 output voltage
Minimum DPP 4 output voltage
DPP 4 output
DPP 3 output
DPP 2 output
DPP 1 output
Maximum DPP 4 output voltage
Maximum DPP 3 output voltage
10
11
12
13
14
15
16
17
18
19
20
GND
V
REFL1
V
REFL2
V
REFL3
V
REFL4
V
OUT4
V
OUT3
V
OUT2
V
OUT1
V
REFH4
V
REFH3
DEVICE OPERATION
The CAT525 is a quad 8-bit configured digitally
programmable potentiometer (DPP/CDPP) whose
outputs can be programmed to any one of 256 individual
voltage steps. Once programmed, these output settings
are retained in non-volatile memory and will not be lost
when power is removed from the chip. Upon power up
the DPPs return to the settings stored in non-volatile
memory. Each confitured DPP can be written to and
read from independently without effecting the output
voltage during the read or write cycle. Each output can
also be adjusted without altering the stored output
setting, which is useful for testing new output settings
before storing them in memory.
DIGITAL INTERFACE
The CAT525 employs a 3 wire serial, Microwire-like
control interface consisting of Clock (CLK), Chip Select
(CS) and Data In (DI) inputs. For all operations, address
and data are shifted in LSB first. In addition, all digital
data must be preceded by a logic “1” as a start bit. The
DPP address and data are clocked into the DI pin on the
clock’s rising edge. When sending multiple blocks of
information a minimum of two clock cycles is required
between the last block sent and the next start bit.
Multiple devices may share a common input data line by
selectively activating the CS control of the desired IC.
Data Outputs (DO) can also share a common line
because the DO pin is Tri-Stated and returns to a high
impedance when not in use.
CHIP SELECT
Chip Select (CS) enables and disables the CAT525’s
read and write operations. When CS is high data may be
read to or from the chip, and the Data Output (DO) pin is
active. Data loaded into the DPP wiper control registers
will remain in effect until CS goes low. Bringing CS to a
logic low returns all DPP outputs to the settings stored in
non-volatile memory and switches DO to its high
impedance Tri-State mode.
Because CS functions like a reset the CS pin has been
desensitized with a 30 ns to 90 ns filter circuit to prevent
noise spikes from causing unwanted resets and the loss
of volatile data.
CLOCK
The CAT525’s clock controls both data flow in and out of
the IC and non-volatile memory cell programming. Serial
data is shifted into the DI pin and out of the DO pin on the
clock’s rising edge. While it is not necessary for the clock
to be running between data transfers, the clock must be
operating in order to write to non-volatile memory, even
though the data being saved may already be resident in
the DPP wiper control register.
No clock is necessary upon system power-up. The
CAT525’s internal power-on reset circuitry loads data
from non-volatile memory to the DPPs without using the
external clock.
CDPP/DPP addressing is as follows:
DPP OUTPUT
A0
A1
V
OUT1
V
OUT2
V
OUT3
V
OUT4
0
0
1
0
0
1
1
1