MAX6920 Maxim Integrated Products, MAX6920 Datasheet - Page 6

• Manufacturer Part Number: MAX6920
• Description: Serial-Interfaced VFD Tube Driver
• Manufacturer: Maxim Integrated Products

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12-Output, 76V, Serial-Interfaced
VFD Tube Driver
Figure 2. MAX6920 CMOS Output Driver Structure
The MAX6920 is a VFD tube driver comprising a 4-wire
serial interface driving 12 high-voltage Rail-to-Rail®
output ports. The driver is suitable for both static and
multiplexed displays.
The output ports feature high current-sourcing capabili-
ty to drive current into grids and anodes of static or
multiplex VFDs. The ports also have active current sink-
ing for fast discharge of capacitive display electrodes
in multiplexing applications.
The 4-wire serial interface comprises a 12-bit shift reg-
ister and a 12-bit transparent latch. The shift register is
written through a clock input CLK and a data input DIN
and the data propagates to a data output DOUT. The
data output allows multiple drivers to be cascaded and
operated together. The output latch is transparent to
Figure 3. 4-Wire Serial Interface Timing Diagram
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
6
DOUT
LOAD
CLK
DIN
_______________________________________________________________________________________
SLEW- RATE
CONTROL
Detailed Description
V
BB
40Ω
TYPICAL
750Ω
TYPICAL
t
DS
D11
OUT_
t
DH
t
CL
D10
t
CH
the shift register outputs when LOAD is high, and latch-
es the current state on the falling edge of LOAD.
Each driver output is a slew-rated controlled CMOS
push-pull switch driving between V
output rise time is always slower than the output fall
time to avoid shoot-through currents during output tran-
sitions. The output slew rates are slow enough to mini-
mize EMI, yet are fast enough so as not to impact the
typical 100µs digit multiplex period and affect the dis-
play intensity.
An internal reset circuit clears the internal registers of
the MAX6920 on power-up. All outputs OUT0 to OUT11
and the interface output DOUT initialize low regardless
of the initial logic levels of the CLK, DIN, BLANK, and
LOAD inputs.
The MAX6920 uses a 4-wire serial interface with three
inputs (DIN, CLK, LOAD) and a data output (DOUT).
This interface is used to write output data to the
MAX6920
word length is 12 bits, D0–D11.
The functions of the four serial interface pins are:
•
•
CLK input is the interface clock, which shifts data
into the MAX6920’s 12-bit shift register on its rising
edge.
LOAD input passes data from the MAX6920’s 12-
bit shift register to the 12-bit output latch when
LOAD is high (transparent latch), and latches the
data on LOAD’s falling edge.
D1
t
DO
(Figure
t
Initial Power-Up and Operation
CP
3)
(Table
D0
t
CSH
4-Wire Serial Interface
1). The serial interface data
D11
t
CSW
BB
and GND. The