Rainbow Electronics MAX5839 - Manual (Page 9)

MAX5839
Octal, 13-Bit Voltage-Output DAC
with Parallel Interface
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_______________Detailed Description
Analog Section
The MAX5839 contains eight 13-bit voltage-output
DACs. These DACs are “inverted” R-2R ladder net-
works that convert 13-bit digital inputs into equivalent
analog output voltages, in proportion to the applied ref-
erence voltages (Figure 1). The MAX5839 has three
positive reference inputs (REF_ _ _ _+) and three nega-
tive reference inputs (REF_ _ _ _-). The difference from
REF_ _ _ _+ to REF_ _ _ _- , multiplied by two, sets the
DAC output span.
In addition to the differential reference inputs, the
MAX5839 has four analog-ground input pins (DUT-
GND_ _). When CLR is high (unasserted), the voltage
on DUTGND_ _ offsets the DAC output voltage range. If
CLR is asserted, the output amplifier is forced to the
voltage present on DUTGND_ _.
Reference and DUTGND Inputs
All of the MAX5839’s reference inputs are buffered with
precision amplifiers. This allows the flexibility of using
resistive dividers to set the reference voltages. Because
of the relatively high multiplying bandwidth of the refer-
ence input (188kHz), any signal present on the refer-
ence pin within this bandwidth is replicated on the DAC
output.
The DUTGND pins of the MAX5839 are connected to
the negative source resistor (nominally 84k
Ω) of the
output amplifier. The DUTGND pins are typically con-
nected directly to analog ground. Each of these pins
has an input current that varies with the DAC digital
code. If the DUTGND pins are driven by external cir-
cuitry, budget ±200µA per DAC for load current.
Output Buffer Amplifiers
The MAX5839’s voltage outputs are internally buffered
by precision gain-of-two amplifiers with a typical slew
rate of 1V/µs. With a full-scale transition at its output,
the typical settling time to ±
1 / 2 LSB is 22µs. This settling
time does not significantly vary with capacitive loads
less than 10,000pF.
Output Deglitching Circuit
The MAX5839’s internal connection from the DAC lad-
der to the output amplifier contains special deglitch cir-
cuitry. This glitch/deglitch circuitry is enabled on the
falling edge of LD to remove the glitch from the R-2R
DAC. This enables the MAX5839 to exhibit a fraction of
the glitch impulse energy of parts without the deglitch-
ing circuit.
REF-
REF+
2R 2R 2R 2R 2R
OUT
DUTGND
2R
CLR
R R
D0 D11 D12
Figure 1. DAC Simplified Circuit
CS
WR
A0–A2
D0–D12
LD
NOTES:
(NOTE 3)
1. ALL INPUT RISE AND FALL TIMES MEASURED FROM 10% TO 90% OF
+5V. t r = t f = 5ns.
2. MEASUREMENT REFERENCE LEVEL IS (V INH + V INL ) / 2.
3. IF LD– IS ACTIVATED WHILE WR IS LOW, THEN LD– MUST STAY LOW
FOR t 3 OR LONGER AFTER WR GOES HIGH.
t
1
t 2
t 8
t
9
t 6 t 7
t 4 t 5
t 3
t 3
Figure 2. Digital Timing Diagram