14
For more information www.linear.com/LTC2640
typical perFormance characteristics
LTC2640
Multiplying Bandwidth
Noise Voltage vs Frequency
0.1Hz to 10Hz Voltage Noise
pin Functions
CS/LD (Pin 1): Serial Interface Chip Select/Load Input.
When CS/LD is low, SCK is enabled for shifting data on
SDI into the register. When CS/LD is taken high, SCK
is disabled and the specified command (see Table 1) is
executed.
SCK (Pin 2): Serial Interface Clock Input. CMOS and TTL
compatible.
SDI (Pin 3): Serial Interface Data Input. Data on SDI
is clocked into the DAC on the rising edge of SCK. The
LTC2640 accepts input word lengths of either 24- or 32-bits.
GND (Pin 4): Ground.
V
CC
(Pin 5): Supply Voltage Input. 2.7V ≤ V
CC
≤ 5.5V
(LTC2640-L) or 4.5V ≤ V
CC
≤ 5.5V (LTC2640-H). Bypass
to GND with a 0.1µF capacitor.
REF (Pin 6): Reference Voltage Input or Output. When
External Reference mode is selected, REF is an input
(0V ≤ V
REF
≤ V
CC
) where the voltage supplied sets the
full-scale voltage. When Internal Reference is selected,
the 10ppm/°C 1.25V (LTC2640-L) or 2.048V (LTC2640-H)
internal reference is
available at the pin. This output may
be bypassed to GND with up to 10µF (0.33µF is recom-
mended), and
must
be buffered when driving external DC
load current.
V
OUT
(Pin 7): DAC Analog Voltage Output.
CLR (Pin 8, LTC2640-Z): Asynchronous Clear
Input. A
logic low at this level-triggered input clears all registers
and causes the DAC voltage output to reset to Zero. CMOS
and TTL compatible.
REF_SEL (Pin 8, LTC2640-M): Selects default Reference
at power-up. Tie to V
CC
to select the Internal Reference,
or GND to select an External Reference. After power-up,
the logic state at this pin is ignored and the reference may
be changed only by software command.
FREQUENCY (Hz)
100
200
300
1M
2640 G34
100
0
1k
10k
100k
400
INTERNAL REF.
CODE = MIDSCALE
LTC2640-H
(V
CC
= 5V)
LTC2640-L
(V
CC
= 4V)
1s/DIV
10µV/DIV
2640 G35
LTC2640-L, V
CC
= 4V
INTERNAL REF.
CODE = MIDSCALE
FREQUENCY (Hz)
1k
dB
–2
–6
–8
–14
–4
–12
–10
–16
–18
100k
2640 G33
1000k10k
V
CC
= 5V
V
REF(DC)
= 2V
V
REF(AC)
= 0.2V
P-P
CODE = FULL SCALE
T
A
= 25°C, unless otherwise noted.
