19-2635; Rev 1; 1/03
4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-
numeric Vacuum-Fluorescent Display Controller
General Description
The MAX6850 compact vacuum-fluorescent display
(VFD) controller provides microprocessors with the mul-
tiplex timing for 7-segment, 14-segment, or 16-segment
alphanumeric VFD displays up to 96 characters and
controls industry-standard, shift-register, high-voltage
grid/anode VFD tube drivers. The device supports dis-
play tubes using either one or two digits per grid, as
well as universal displays. Hardware is included to sim-
plify the generation of cathode bias and filament sup-
plies and to provide up to five logic outputs, including a
buzzer driver. The MAX6850 provides an internal cross-
point switch to match any tube-driver shift-register
grid/anode order, and is compatible with both chip-in-
glass and external tube drivers.
The MAX6850 includes an ASCII 104-character font,
multiplex scan circuitry, and static RAM that stores
digit, cursor, and annunciator data, as well as font data
for 24 user-definable characters. The display intensity
can be adjusted by an internal 16-step digital bright-
ness control. The device also includes separate annun-
ciator and cursor control with automatic blinking, as
well as a low-power shutdown mode.
The MAX6850 provides timing to generate the PWM
waveforms to drive the tube filament from a DC supply.
The filament drive is synchronized to the display multi-
plexing to eliminate beat artifacts. The MAX6850 is
compatible with SPI™ and QSPI™.
For a 2-wire interfaced version, refer to the MAX6851*
data sheet.
*Future product—contact factory for availability.
Features
o
High-Speed 26MHz SPI-/QSPI-/MICROWIRE™-
Compatible Serial Interface
o
2.7V to 3.6V Operation
o
Controls Up to 48 Grids of 7-Segment, 14-Segment,
or 16-Segment Alphanumeric Digits
o
One Digit and Two Digits per Grid and Universal
Displays Supported
o
16-Step Digital Brightness Control
o
Built-In ASCII 104-Character Font
o
24 User-Definable Characters
o
Up to Four Annunciators per Grid with Automatic
Blinking Control
o
Separate Cursor Control with Automatic Blinking
o
Filament Drive Full-Bridge Waveform Synthesis
o
Buzzer Tone Generator with Single-Ended or
Push-Pull Driver
o
Up to Five General-Purpose Logic Outputs
o
9µA Low-Power Shutdown (Data Retained)
o
16-Pin QSOP Package
MAX6850
Ordering Information
PART
MAX6850AEE
TEMP RANGE
-40°C to +125°C
PIN-PACKAGE
16 QSOP
Applications
Display Modules
Retail POS Displays
Weight and Tare
Displays
Bar Graph Displays
Industrial Controllers
White Goods
Professional Audio
Equipment
Typical Application Circuit
CHIP-ON-GLASS VFD
VFD SUPPLY VOLTAGE
0.1µF
MICROCONTROLLER
VFCLK
MAX6850
VFDOUT
DOUT
DIN
VFLOAD
SCLK
VFBLANK
CS
CS
OSC2
Pin Configuration and Functional Diagram appear at end of
data sheet.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
SCLK
GND
OSC1
10kΩ
56pF
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-
numeric Vacuum-Fluorescent Display Controller
MAX6850
ABSOLUTE MAXIMUM RATINGS
Voltage (with respect to GND)
V+ .............................................................................-0.3V to +4V
DIN, SCLK,
CS
......................................................-0.3V to +5.5V
All Other Pins................................................-0.3V to (V+ + 0.3V)
Current
V+..................................................................................200mA
GND .............................................................................-200mA
PHASE1, PHASE2, PORT0, PORT1, PUMP................±150mA
VFCLK, VFDOUT, VFLOAD, VFBLANK ......................±150mA
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate at 8.34mW/°C above +70°C).....667mW
Operating Temperature Range (T
MIN
, T
MAX
)
MAX6850AEE................................................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(Typical operating circuit, V+ = 2.7V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Note 1)
PARAMETER
Operating Supply Voltage
Shutdown Supply Current
SYMBOL
V+
I
SHDN
Shutdown mode, all digital
inputs at V+ or GND
OSC = 4MHz
VFLOAD, VFDOUT, VFCLK,
VFBLANK, loaded 100pF
T
A
= T
MIN
to
T
MAX
T
A
= +25°C
Operating Supply Current
I+
T
A
= T
MIN
to
T
MAX
T
A
= +25°C
1.7
4
9
CONDITIONS
MIN
2.7
TYP
MAX
3.6
85
30
3.5
3.0
MHz
mA
UNITS
V
µA
Master Clock Frequency (OSC
Internal Oscillator)
Master Clock Frequency (OSC
External Oscillator)
Dead-Clock Protection
Frequency
OSC High Time
OSC Low Time
Fast or Slow Segment Blink Duty
Cycle
LOGIC INPUTS AND OUTPUTS
Input Leakage Current DIN,
SCLK,
CS
Logic-High Input Voltage DIN,
SCLK,
CS
Logic-Low Input Voltage DIN,
SCLK,
CS
f
OSC
OSC1 fitted with C
OSC
= 56pF, OSC2 fitted
with R
OSC
= 10kΩ; see the
Typical
Operating Circuit
OSC1 overdriven with external f
OSC
2
8
200
MHz
kHz
ns
ns
t
CH
t
CL
(Note 2)
50
50
49.5
50.5
%
I
IH
, I
IL
V
IH
V
IL
2.4
0.2
1
µA
V
0.6
V
2
_______________________________________________________________________________________
4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-
numeric Vacuum-Fluorescent Display Controller
DC ELECTRICAL CHARACTERISTICS (continued)
(Typical operating circuit, V+ = 2.7V to 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.) (Note 1)
PARAMETER
Output Rise and Fall Time
PHASE1, PHASE2, PORT0,
PORT1, PUMP, VFLOAD,
VFDOUT, VFCLK, VFBLANK
Output High-Voltage
PHASE1, PHASE2, PORT0,
PORT1, PUMP, VFLOAD,
VFDOUT, VFCLK, VFBLANK
Output Low-Voltage
PHASE1, PHASE2, PORT0,
PORT1, PUMP, VFLOAD,
VFDOUT, VFCLK, VFBLANK
Output Short-Circuit Source
Current PHASE1, PHASE2,
PORT0, PORT1, PUMP, VFLOAD,
VFDOUT, VFCLK, VFBLANK
Output Short-Circuit Sink Current
PHASE1, PHASE2, PORT0,
PORT1, PUMP, VFLOAD,
VFDOUT, VFCLK, VFBLANK
SCLK Clock Period
SCLK Pulse Width High
SCLK Pulse Width Low
CS
Fall to SCLK Rise Setup Time
SCLK Rise to
CS
Rise Hold Time
DIN Setup Time
DIN Hold Time
Minimum
CS
Pulse High
DOUT Cascade Setup Time
PORT0, PORT1
VFCLK Clock Period
VFCLK Pulse Width High
VFCLK Pulse Width Low
VFCLK Rise to VFD Load Rise
Hold Time
VFDOUT Setup Time
VFLOAD Pulse High
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX6850
t
RFT
C
LOAD
= 100pF
25
ns
V
OH
I
SOURCE
= 10 mA
V+ - 0.6
V
V
OL
I
SINK
= 10 mA
0.4
V
I
OHSC
Output programmed high, output short
circuit to GND (Note 2)
62
125
mA
I
OLSC
Output programmed low, output short
circuit to V+ (Note 2)
72
125
mA
4-WIRE SERIAL INTERFACE TIMING CHARACTERISTICS
(Figure 8)
t
CP
t
CH
t
CL
t
CSS
t
CSH
t
DS
t
DH
t
CSW
t
CSU
PORT0 and/or PORT1 enabled as DOUT
38.4
19
19
9.5
5
9.5
2
19
9.5
ns
ns
ns
ns
ns
ns
ns
ns
ns
VFD INTERFACE TIMING CHARACTERISTICS
(Figure 11)
t
VCP
t
VCH
t
VCL
t
VCSH
t
VDS
t
VCSW
(Note 2)
(Note 2)
(Note 2)
(Note 2)
(Note 2)
(Note 2)
500
250
250
19
50
245
2050
ns
ns
ns
µs
ns
ns
Note 1:
All parameters tested at T
A
= +25°C. Specifications over temperature are guaranteed by design.
Note 2:
Guaranteed by design.
_______________________________________________________________________________________
3
4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-
numeric Vacuum-Fluorescent Display Controller
MAX6850
Typical Operating Characteristics
(Typical Operating Circuit, V+ = 3.3V, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6850 toc01
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6850 toc02
SHUTDOWN SUPPLY CURRENT
vs. EXTERNAL OSC FREQUENCY
MAX6850 toc03
2.2
2.1
2.0
ISUPPLY
(mA)
50
45
40
35
ISUPPLY
(µA)
OSC1 = 0
T
A
= +125°C
1400
1200
1000
ISUPPLY
(µA)
1.9
1.8
1.7
1.6
1.5
2.7
2.9
T
A
= +125°C
T
A
= -40°C
30
25
20
15
10
5
0
T
A
= +25°C
T
A
= -40°C
800
600
400
200
0
3.1
V+ (V)
3.3
3.5
3.7
2.7
2.9
3.1
V+ (V)
3.3
3.5
2
3
4
5
6
7
8
FREQUENCY (MHz)
OUTPUT LOW VOLTAGE vs. I
SINK
MAX6850 toc04
OUTPUT LOW VOLTAGE vs. I
SINK
MAX6850 toc05
OUTPUT LOW VOLTAGE vs. I
SINK
1.8
1.6
1.4
VOL
(V)
MAX6850 toc06
2.0
1.8
1.6
1.4
VOL
(V)
2.0
1.8
1.6
1.4
VOL
(V)
2.0
V+ = 2.7V
V+ = 3.3V
V+ = 2.7V
V+ = 3.3V
V+ = 2.7V
V+ = 3.3V
1.2
1.0
0.8
0.6
0.4
0.2
0
0
20
40
60
ISINK
(mA)
80
100
V+ = 3.6V
T
A
= -40°C
1.2
1.0
0.8
0.6
0.4
0.2
0
0
20
40
60
ISINK
(mA)
80
100
T
A
= +25°C
V+ = 3.6V
1.2
1.0
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
ISINK
(mA)
V+ = 3.6V
T
A
= +125°C
V
IN
- V
OH
vs. I
SOURCE
MAX6850 toc07
V
IN
- V
OH
vs. I
SOURCE
MAX6850 toc08
V
IN
- V
OH
vs. I
SOURCE
MAX6850 toc09
2.0
V+ = 2.7V
1.5
VOL
(V)
2.0
1.8
1.6
1.4
VOL
(V)
2.0
V+ = 2.7V
1.5
VOL
(V)
V+ = 2.7V
V+ = 3.3V
V+ = 3.3V
V+ = 3.3V
1.2
1.0
0.8
0.6
0.4
0.2
T
A
= +25°C
V+ = 3.6V
1.0
V+ = 3.6V
0.5
T
A
= -40°C
1.0
V+ = 3.6V
0.5
T
A
= +125°C
0
0
20
60
ISOURCE
(mA)
40
80
100
0
0
20
60
ISOURCE
(mA)
40
80
100
0
0
20
60
ISOURCE
(mA)
40
80
100
4
_______________________________________________________________________________________
4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-
numeric Vacuum-Fluorescent Display Controller
Typical Operating Characteristics (continued)
(Typical Operating Circuit, V+ = 3.3V, T
A
= +25°C, unless otherwise noted.)
f
OSC
vs. TEMPERATURE
V+ = 2.7V
2.0
V+ = 3.3V
MAX6850 toc10
MAX6850
DEAD-CLOCK OSC FREQUENCY
vs. TEMPERATURE
0.16
0.14
FREQUENCY (MHz)
0.12
0.10
0.08
0.06
V+ = 2.7V
0.04
0.02
V+ = 3.3V
V+ = 3.6V
MAX6850 toc11
2.5
0.18
f
OSC
(MHz)
1.5
V+ = 3.6V
1.0
0.5
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
NAME
VFCLK
VFDOUT
VFLOAD
VFBLANK
PUMP
PHASE1
PHASE2
V+
GND
PORT0
SCLK
DIN
CS
PORT1
FUNCTION
Serial-Clock Output to External Driver. Push-pull clock output to external display driver. On VFCLK’s
falling edge, data is clocked out of VFDOUT.
Serial-Data Output to External Driver. Push-pull data output to external display driver.
Serial-Load Output to External Driver. Push-pull load output to external display driver. Rising edge is
used by external display driver to load serial data into display latch.
Display Blanking Output to External Driver. Push-pull blanking output to external display driver used for
PWM intensity control.
Charge-Pump Output and General-Purpose Output. User-configurable push-pull logic output can also
be used as a driver for external charge pump.
Filament Drive PHASE1 Output and General-Purpose Output. User-configurable push-pull logic output
can also be used as a driver for external filament bridge drive.
Filament Drive PHASE2 Output and General-Purpose Output. User-configurable push-pull logic output
can also be used as a driver for external filament bridge drive.
Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor.
Ground
PORT0 General-Purpose Output. User-configurable push-pull logic output.
Serial-Clock Input. On SCLK’s rising edge, data shifts into the internal shift register, and data is
clocked out of DOUT. SCLK is active only while
CS
is low.
Serial-Data Input. Data from DIN loads into the internal 16-bit shift register on SCLK’s rising edge.
Chip-Select Input. Serial data is loaded into the shift register while
CS
is low. The most recent 16 bits of
data latch on
CS’s
rising edge.
PORT1 General-Purpose Output. User-configurable push-pull logic output.
_______________________________________________________________________________________
5
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