AN874 [MAXIM]

Using the MAX6950 and the MAX6951 LED Display Drivers with Multiplex Dual-Digit Displays; 使用MAX6950和复用双数字显示了MAX6951 LED显示驱动器
AN874
元器件型号: AN874
生产厂家: MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述和应用:

Using the MAX6950 and the MAX6951 LED Display Drivers with Multiplex Dual-Digit Displays
使用MAX6950和复用双数字显示了MAX6951 LED显示驱动器

显示驱动器
PDF文件: 总6页 (文件大小:42K)
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DISPLAY DRIVERS
Apr 01, 2002
Using the MAX6950 and the MAX6951 LED Display
Drivers with Multiplex Dual-Digit Displays
This application note discusses how to connect the MAX6950 (5 digit) and
MAX6951 (8 digit) 7-segment LED display drivers to multiplex dual digit LED
displays instead of regular single digit 7 segment displays.
This application note discusses how to connect the MAX6950 and MAX6951 7-segment LED display
drivers to multiplex type (internally communed) dual digit displays, instead of regular single digit
displays.
The MAX6950 and MAX6951 are five-digit and eight-digit common-cathode LED display drivers that
use an unusual multiplexing scheme. This multiplexing scheme minimizes the connections between the
driver and the LED display, but requires the segment connections to be different to each of the five
(MAX6950) or eight (MAX6951) digits (Table 1).
Table 1. Standard Driver Connections to Single-Digit Displays
SEG8
DIG0/SEG0 DIG1/SEG1 DIG2/SEG2 DIG3/SEG3 DIG4/SEG4 DIG5/SEG5 DIG6/SEG6 DIG7/SEG7
Pin
Pin 5
Pin 4
Pin 3
Pin 14
Pin 13
Pin 12
Pin 11
Pin 6
10
LED
Digit
0
LED
Digit
1
LED
Digit
2
LED
Digit
3
LED
Digit
4
LED
Digit
5*
CC 0
SEG dp
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
SEG
a
SEG
a
SEG
a
SEG
a
SEG
a
SEG
a
SEG dp
CC1
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
SEG dp
SEG g
CC2
SEG f
SEG e
SEG d
SEG c
SEG b
SEG dp
SEG g
SEG f
CC3
SEG e
SEG d
SEG c
SEG b
SEG dp
SEG g
SEG f
SEG e
CC4
SEG d
SEG c
SEG b
SEG dp
SEG g
SEG f
SEG e
SEG d
CC5
SEG c
SEG b
LED
Digit
6*
LED
Digit
7*
SEG dp
SEG g
SEG f
SEG e
SEG d
SEG c
CC6
SEG b
SEG
a
SEG
a
SEG dp
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
CC7
*These digits are not available for the MAX6950.
The MAX6950 and MAX6951 were intended to drive single-digit displays, and this allows the segments
for each digit to be routed to the correct driver pin. Many dual-digit displays pin out the two digits
separately, treating the digits as two singles in one package. These can be driven directly by the
MAX6950 and MAX6951. Other dual-digit displays internally pair the segment anodes for the two digits
(Figure 1) and these displays present issues.
The problem can be understood by checking the SEG dp entries in Table 1 for Digit 0 and Digit 1. SEG
dp is connected to a different pin for each digit. However, a multiplex dual-digit display commons these
connections internally (Figure 1), effectively shorting Pin 5 and Pin 6 of the driver.
Figure 1. Internal connections for a multiplex dual-digit display
Two simple solutions are presented here.
The first solution simply sacrifices the segment drive that share a cathode drive for each dual-digit. This
is SEG dp for Digit 0 and Digit 1 discussed earlier. By examining Table 1, it can be seen that the other
sacrificed segments are SEG f for Digit 2 and Digit 3, SEG d for Digit 4 and Digit 5, and SEG b for Digit
6 and Digit 7. However, it's usually the DP segments that applications can sacrifice, not segments
within the seven-segment digit.
If the DPs are not required, then the connections shown in Table 2 can be used. This is a rework of the
standard connections shown in Table 1, with the segments moved so that all segments apart from the
DP segments are available. The DP segment connections on the displays are simply left unused. The
no-decode operation should not be selected when this (or any other nonstandard) pin mapping is used.
The MAX6950 or MAX6951's internal hexadecimal fonts display correctly in decode mode only when
the standard display connections are being used.
Table 2. Example Driver Connections to Dual-Digit Displays When No DPs Are Required
SEG8
DIG0/SEG0 DIG1/SEG1 DIG2/SEG2 DIG3/SEG3 DIG4/SEG4 DIG5/SEG5 DIG6/SEG6 DIG7/SEG7
Pin
Pin 6
Pin 5
Pin 4
Pin 3
Pin 14
Pin 13
Pin 12
Pin 11
10
LED
Digit
0
LED
Digit
1
LED
Digit
2
LED
Digit
3
LED
Digit
4
LED
Digit
5*
LED
Digit
6*
LED
Digit
7*
CC 0
-unused-
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
SEG
a
SEG
a
SEG
a
SEG
a
SEG
a
SEG
a
SEG
a
SEG
a
-unused-
CC1
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
SEG f
SEG g
CC2
-unused-
SEG e
SEG d
SEG c
SEG b
SEG f
SEG g
-unused-
CC3
SEG e
SEG d
SEG c
SEG b
SEG d
SEG g
SEG f
SEG e
CC4
-unused-
SEG c
SEG b
SEG d
SEG g
SEG f
SEG e
-unused-
CC5
SEG c
SEG b
SEG b
SEG g
SEG f
SEG e
SEG d
SEG c
CC6
-unused-
SEG b
SEG g
SEG f
SEG e
SEG d
SEG c
-unused-
CC7
*These digits are not available for the MAX6950.
The unused segment drives in the Table 2 connection need not be wasted. They can be used to drive
up to 8 discrete LEDs, to take place of each unused dp segment per digit. This is shown in Table 3.
Table 3. Example Driver Connections to Dual-Digit Displays When No DPs Are Required, Plus 8
Discrete LEDs
SEG8
DIG0/SEG0 DIG1/SEG1 DIG2/SEG2 DIG3/SEG3 DIG4/SEG4 DIG5/SEG5 DIG6/SEG6 DIG7/SEG7
Pin
Pin 6
Pin 5
Pin 4
Pin 3
Pin 14
Pin 13
Pin 12
Pin 11
10
LED
Digit
0
Discrete
LED anode
(cathode to
CC1)
SEG
a
CC 0
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
Discrete
LED
LED anode
Digit
(cathode to
1
CC0)
LED
Digit
2
LED
Digit
3
LED
Digit
4
LED
Digit
5*
LED
Digit
6*
LED
Digit
7*
CC1
SEG g
SEG f
Discrete
LED anode
(cathode to
CC3)
SEG e
SEG d
SEG c
SEG b
SEG
a
SEG f
SEG g
CC2
SEG e
SEG d
SEG c
SEG b
SEG
a
SEG f
SEG g
Discrete
LED anode
(cathode to
CC2)
CC3
SEG e
SEG d
Discrete
LED anode
(cathode to
CC5)
SEG c
SEG b
SEG
a
SEG d
SEG g
SEG f
SEG e
CC4
SEG c
SEG b
SEG
a
SEG d
SEG g
SEG f
SEG e
Discrete
LED anode
(cathode to
CC4)
CC5
SEG c
SEG b
SEG
a
SEG b
SEG g
SEG f
SEG e
SEG d
SEG c
CC6
Discrete
LED anode
(cathode to
CC6)
Discrete
LED anode SEG
(cathode to
a
CC7 )
SEG
a
SEG b
SEG g
SEG f
SEG e
SEG d
SEG c
CC7
*These digits are not available for the MAX6950.
The second solution can be used if all digits' segments are required. This time, hexadecimal-decode
operation can be selected because the standard segment connection pattern is used (Table 4). The
penalty for this configuration is that one diode is required per digit (Figure 2). Each diode is passing
only one segment's current, so it can be a low-cost single signal diode like 1N4148, BAS16 (silicon), or
BAT54, BAR43 (Schottky). Better still, use surface mount dual common-cathode diodes like BAV70
(silicon) and BAT54C (Schottky). The minimum supply voltage to the MAX6950/MAX6951 must also be
raised by the selected diode's forward voltage drop: typically 1.0V for a silicon signal diode or 0.4V for
a Schottky signal diode at 50mA.
Figure 2. External connections to modify a dual-digit display so that all segments are available
Figure 2 shows the correct wiring to the dual-digit used as Digit 0 and Digit 1, which uses external
diodes in series with the dp segments. The connections shown in Table 4 show which segments
require diodes for the other three dual-digits.
Table 4. Driver Connections to Dual-Digit Displays When All Segments Are Required
SEG8
DIG0/SEG0 DIG1/SEG1 DIG2/SEG2 DIG3/SEG3 DIG4/SEG4 DIG5/SEG5 DIG6/SEG6 DIG7/SEG7
Pin
Pin 6
Pin 5
Pin 4
Pin 3
Pin 14
Pin 13
Pin 12
Pin 11
10
LED
Digit
0
CC 0
Diode to
SEG dp of
Digit 0 and
Digit 1
SEG g
SEG f
SEG e
SEG d
SEG c
SEG b
SEG
a
Diode to
LED
SEG dp of
Digit
Digit 0 and
1
Digit 1
LED
Digit
2
LED
Digit
3
LED
Digit
4
LED
Digit
5*
CC1
SEG g
SEG f
Diode to
SEG f of
Digit 2 and
Digit 3
SEG e
SEG d
SEG c
SEG b
SEG
a
SEG dp
SEG g
CC2
SEG e
SEG d
SEG c
SEG b
SEG
a
SEG dp
SEG g
Diode to
SEG f of
Digit 2 and
Digit 3
CC3
SEG e
SEG d
Diode to
SEG d of
Digit 4 and
Digit 5
SEG c
SEG b
SEG
a
SEG dp
SEG g
SEG f
SEG e
CC4
SEG c
SEG b
SEG
a
SEG dp
SEG g
SEG f
SEG e
Diode to
SEG d of
Digit 4 and
Digit 5
CC5
SEG c
SEG b
SEG
a
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    AN874
    描述和应用

    Using the MAX6950 and the MAX6951 LED Display Drivers with Multiplex Dual-Digit Displays
    使用MAX6950和复用双数字显示了MAX6951 LED显示驱动器

    显示驱动器
    总6页 (42K) MAXIM INTEGRATED PRODUCTS
    MAXIM INTEGRATED PRODUCTS
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