MC1408-8 Datasheet, PDF (5/10 Pages) NXP Semiconductors – 8-bit multiplying D/A converter

Philips Semiconductors
8-bit multiplying D/A converter
Product data
MC1408-8
TYPICAL PERFORMANCE CHARACTERISTICS
D-to-A TRANSFER CHARACTERISTICS
0
1.0
2.0
(00000000) INPUT DIGITAL WORD (11111111)
SL00050
Figure 3. Typical Performance Characteristics
FUNCTIONAL DESCRIPTION
Reference Amplifier Drive and Compensation
The reference amplifier input current must always flow into Pin 14.
regardless of the setup method or reference supply voltage polarity.
Connections for a positive reference voltage are shown in Figure 4.
The reference voltage source supplies the full reference current. For
bipolar reference signals, as in the multiplying mode, R₁₅ can be
tied to a negative voltage corresponding to the minimum input level.
R₁₅ may be eliminated and Pin 15 grounded, with only a small
sacrifice in accuracy and temperature drift.
V_CC
A1 ⁵
A2 ⁶
7
A3
8
A4
9
A5
10
A6
A7 ¹¹
A8 ¹²
13
14
15
1
MC1408 ²
4
16
3
R₁₄ = R₁₅
R₁₄
(+)V_REF
R₁₅
R_L
I_O
SEE TEXT FOR VALUES OF C.
C
V_EE
Figure 4. Positive V_REF
SL00051
The compensation capacitor value must be increased with
increasing values of R₁₄ to maintain proper phase margin. For R₁₄
values of 1.0, 2.5, and 5.0 kΩ, minimum capacitor values are 15, 37,
and 75 pF. The capacitor may be tied to either V_EE or ground, but
using V_EE increases negative supply rejection. (Fluctuations in the
negative supply have more effect on accuracy than do any changes
in the positive supply.)
A negative reference voltage may be used if R₁₄ is grounded and
the reference voltage is applied to R₁₅, as shown in Figure 5. A high
input impedance is the main advantage of this method. The negative
reference voltage must be at least 3.0 V above the V_EE supply.
Bipolar input signals may be handled by connecting R₁₄ to a positive
reference voltage equal to the peak positive input level at Pin 15.
Capacitive bypass to ground is recommended when a DC reference
voltage is used. The 5.0 V logic supply is not recommended as a
reference voltage, but if a well regulated 5.0 V supply which drives
logic is to be used as the reference, R₁₄ should be formed of two
series resistors and the junction of the two resistors bypassed with
0.1 µF to ground. For reference voltages greater than 5.0 V, a clamp
diode is recommended between Pin 14 and ground.
If Pin 14 is driven by a high impedance such as a transistor current
source, none of the above compensation methods apply and the
amplifier must be heavily compensated, decreasing the overall
bandwidth.
V_CC
A1 ⁵
A2 ⁶
7
A3
8
A4
9
A5
10
A6
A7 ¹¹
A8 ¹²
13
14
15
1
MC1408 2
4
16
3
R₁₄ = R₁₅
R₁₄
(–)V_REF
R₁₅
R_L
I_O
SEE TEXT FOR VALUES OF C.
C
V_EE
Figure 5. Negative V_REF
SL00052
Output Voltage Range
The voltage at Pin 4 must always be at least 4.5 V more positive
than the voltage of the negative supply (Pin 3) when the reference
current is 2 mA or less, and at least 8 V more positive than the
negative supply when the reference current is between 2 mA and
4 mA. This is necessary to avoid saturation of the output transistors,
which would cause serious degradation of accuracy.
Philips Semiconductors MC1408-8 does not need a range control
because the design extends the compliance range down to 4.5 V (or
8 V — see above) above the negative supply voltage without
significant degradation of accuracy. Philips Semiconductors
MC1408-8 can be used in sockets designed for other
manufacturers’ MC1408 without circuit modification.
2001 Aug 03
5