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19-3020; Rev 1; 4/10
20-Output, 76V, Serial-Interfaced VFD Tube Drivers
General Description
The MAX6921/MAX6931 are 20-output, 76V, vacuumfluorescent display (VFD) tube drivers that interface a multiplexed VFD tube to a VFD controller, such as the MAX6850-MAX6853, or to a microcontroller. The MAX6921/MAX6931 are also ideal for driving static VFD tubes or telecom relays. Data is input using an industry standard 4-wire serial interface (CLOCK, DATA, LOAD, BLANK), compatibile with either Maxim's or industry-standard VFD driver and controller. For easy display control, the active-high BLANK input forces all driver outputs low, turning the display off, and automatically puts the MAX6921/MAX6931 into shutdown mode. Display intensity can also be controlled by directly pulse-width modulating the BLANK input. The MAX6921 has a serial interface data output, DOUT, allowing any number of devices to be cascaded on the same serial interface. The MAX6931 has a negative supply voltage input, VSS, allowing the drivers' output swing to be made bipolar to simplify filament biasing in many applications. The MAX6921 is available in 28-pin TSSOP, SO, and PLCC packages. The MAX6931 is available in a 28-pin TSSOP package. Maxim also offers 12-output VFD drivers (MAX6920) and 32-output VFD drivers (MAX6922/MAX6932).
Features
o 5MHz Industry-Standard 4-Wire Serial Interface o 3V to 5.5V Logic Supply Range o 8V to 76V Grid/Anode Supply Range o -11V to 0V Filament Bias Supply (MAX6931 Only) o Push-Pull CMOS High-Voltage Outputs o Outputs can Source 40mA, Sink 4mA Continuously o Outputs can Source 75mA Repetitive Pulses o Outputs can be Paralleled for Higher Current Drive o Any Output can be Used as a Grid or an Anode Driver o Blank Input Simplifies PWM Intensity Control o Small 28-Pin TSSOP Package o -40C to +125C Temperature Range
MAX6921/MAX6931
Ordering Information
PART MAX6921AUI+ MAX6921AWI/V+ MAX6921AQI+ TEMP RANGE -40C to +125C -40C to +125C -40C to +125C PIN-PACKAGE 28 TSSOP 28 Wide SO 28 PLCC
MAX6931AUI+ -40C to +125C 28 TSSOP +Denotes a lead-free(Pb)/RoHS-compliant package. /V denotes an automotive qualified part.
Applications
White Goods Gaming Machines Automotive Avionics Instrumentation Industrial Weighing Security Telecom VFD Modules Industrial Control
C
Typical Operating Circuit
+5V C1 100nF 7 VCC 8 VBB +60V C2 100nF
VFDOUT VFCLK VFLOAD VFBLANK
6 22 23 20
DIN CLK LOAD BLANK VSS 9
20 OUT0-OUT19
-7V C3 100nF
GND 21
Pin Configurations appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
VFD TUBE
MAX6931
20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
ABSOLUTE MAXIMUM RATINGS
Voltage (with respect to GND) VBB .........................................................................-0.3V to +80V VCC ...........................................................................-0.3V to +6V VSS (MAX6931 only) ...............................................-12V to +0.3V VBB - VSS (MAX6931 only) .....................................-0.3V to +80V OUT_ (MAX6921 only) ..................(GND - -0.3V) to (VBB + 0.3V) OUT_ (MAX6931 only) ....................(VSS - -0.3V) to (VBB + 0.3V) All Other Pins..............................................-0.3V to (VCC + 0.3V) OUT_ Continuous Source Current ....................................-45mA OUT_ Pulsed (1ms max, 1/4 max duty) Source Current ...-80mA Total OUT_ Continuous Source Current .........................-540mA Total OUT_ Continuous Sink Current .................................90mA Total OUT_ Pulsed (1ms max, 1/4 max duty) Source Current ...........................................................-960mA OUT_ Sink Current .............................................................15mA CLK, DIN, LOAD, BLANK, DOUT Current .......................10mA Continuous Power Dissipation (TA = +70C) 28-Pin TSSOP (derate 12.8mW/C over +70C)................................................................1025mW 28-Pin Wide SO (derate 12.5mW/C over +70C)................................................................1000mW 28-Pin PLCC (derate 10.5mW/C over +70C)..................................................................842mW Operating Temperature Range (TMIN to TMAX) ...............................................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Soldering Temperature (reflow) Wide SO, TSSOP lead(Pb)-free ...................................+260C PLCC lead(Pb)-free......................................................+245C
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.
ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, VBB = 8V to 76V, VCC = 3V to 5.5V, VSS = -11V to 0V, VBB - VSS 76V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER Logic Supply Voltage Tube Supply Voltage Bias Supply Voltage (MAX6931 Only) Total Supply Voltage (MAX6931 Only) SYMBOL VCC VBB VSS VBB - VSS All outputs OUT_ low, TA = +25C CLK = idle TA = -40C to +125C All outputs OUT_ high, TA = +25C CLK = idle TA = -40C to +125C All outputs OUT_ low Tube Supply Operating Current IBB All outputs OUT_ high All outputs OUT_ low Bias Supply Operating Current (MAX6931 Only) ISS All outputs OUT_ high TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C -0.8 -1.9 -1.4 -1.5 -0.87 -0.38 mA 0.85 78 540 1.65 CONDITIONS MIN 3 8 -11 TYP MAX 5.5 76 0 76 170 200 900 1000 3.0 6.9 1.3 1.4 mA A UNITS V V V V
Logic Supply Operating Current
ICC
2
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, VBB = 8V to 76V, VCC = 3V to 5.5V, VSS = -11V to 0V, VBB - VSS 76V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL VBB 15V IOUT = -25mA High-Voltage OUT_ VBB 15V IOUT = -40mA 8V < VBB < 15V IOUT = -25mA VBB 15V IOUT = 1mA Low-Voltage OUT_ (MAX6921 Only) VL 8V < VBB < 15V IOUT = 1mA VBB 15V IOUT = 1mA Low-Voltage OUT_ (MAX6931 Only) VL 8V < VBB < 15V IOUT = 1mA Rise Time OUT_ (20% to 80%) Fall Time OUT_ (80% to 20%) LOAD Rising to OUT_ Falling Delay LOAD Rising to OUT_ Rising Delay BLANK Rising to OUT_ Falling Delay BLANK Falling to OUT_ Rising Delay Input Leakage Current CLK, DIN, LOAD, BLANK Logic-High Input Voltage CLK, DIN, LOAD, BLANK Logic-Low Input Voltage CLK, DIN, LOAD, BLANK Hysteresis Voltage DIN, CLK, LOAD, BLANK High-Voltage DOUT Low-Voltage DOUT IIH, IIL VIH VIL VI VOH VOL ISOURCE = -1.0mA ISINK = 1.0mA VCC 0.5 0.5 0.6 0.8 x VCC 0.3 x VCC tR tF CONDITIONS TA = +25C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C TA = +25C TA = -40C to +85C TA = -40C to +125C 0.9 0.6 0.9 1.2 0.9 0.5 1.3 0.05 0.8 VBB - 3.5 VBB - 4.0 VBB - 1.2 VBB - 2.5 VBB - 3.0 0.75 1 1.5 1.9 1.1 1.6 2.0 VSS + 0.75 VSS + 1 VSS + 1.5 VSS + 1.9 VSS + 0.8 VSS + 1.1 VSS + 1.6 VSS + 2.0 2 1.5 1.8 2.4 1.8 2.5 10 s s s s s s A V V V V V V V V MIN VBB - 2 VBB - 2.5 TYP MAX UNITS
MAX6921/MAX6931
VBB = 60V, CL = 50pF, RL =2.3k VBB = 60V, CL = 50pF, RL =2.3k (Notes 2, 3) (Notes 2, 3) (Notes 2, 3) (Notes 2, 3)
SERIAL INTERFACE TIMING CHARACTERISTICS
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, VBB = 8V to 76V, VCC = 3V to 5.5V, VSS = -11V to 0V, VBB - VSS 76V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER Rise and Fall Time DOUT CLK Clock Period CLK Pulse-Width High CLK Pulse-Width Low CLK Rise to LOAD Rise Hold DIN Setup Time DIN Hold Time DOUT Propagation Delay LOAD Pulse High tCP tCH tCL tCSH tDS tDH tDO tCSW 3.0V to 4.5V 4.5V to 5.5V CDOUT = 10pF 3.0V to 4.5V 4.5V to 5.5V (Note 2) SYMBOL CONDITIONS CDOUT = 10pF (Note 2) 3V to 4.5V 4.5V to 5.5V 200 90 90 100 5 20 15 25 20 55 120 75 240 150 MIN TYP 60 30 MAX 100 80 UNITS ns ns ns ns ns ns ns ns ns
Note 1: All parameters are tested at TA = +25C. Specifications over temperature are guaranteed by design. Note 2: Guaranteed by design. Note 3: Delay measured from control edge to when output OUT_ changes by 1V.
Typical Operating Characteristics
(VCC = 5.0V, VBB = 76V, and TA = +25C, unless otherwise noted.)
TUBE SUPPLY CURRENT (IBB) vs. TEMPERATURE (OUTPUTS LOW)
MAX6921/31 toc01
TUBE SUPPLY CURRENT (IBB) vs. TEMPERATURE (OUTPUTS HIGH)
MAX6921/31 toc02
LOGIC SUPPLY CURRENT (ICC) vs. TEMPERATURE (OUTPUTS LOW)
350 SUPPLY CURRENT (A) 300 250 200 150 100 50 0 VCC = 5V, CLK = IDLE VCC = 3.3V, CLK = IDLE -40 -20 0 20 40 60 80 100 120 VCC = 3.3V, CLK = 5MHz VCC = 5V, CLK = 5MHz
MAX6921/31 toc03
2.0 1.8 1.6 SUPPLY CURRENT (mA) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -20 0 20 40 VBB = 40V
VBB = 76V
2.0 1.8 1.6 SUPPLY CURRENT (mA) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 VBB = 40V VBB = 8V VBB = 76V
400
VBB = 8V
60
80
100 120
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers
Typical Operating Characteristics (continued)
(VCC = 5.0V, VBB = 76V, and TA = +25C, unless otherwise noted.)
LOGIC SUPPLY CURRENT (ICC) vs. TEMPERATURE (OUTPUTS HIGH)
MAX6921/31 toc04
MAX6921/MAX6931
OUTPUT VOLTAGE (VBB - VH) vs. TEMPERATURE (OUTPUT HIGH)
IOUT = -40mA 3.0 VBB = 8V OUTPUT VOLTAGE (V) 2.5 2.0 VBB = 40V 1.5 1.0 0.5 0 VBB = 76V
MAX6921/31 toc05
800 750 SUPPLY CURRENT (A) 700 650 600 550 500 450 400 -40 -20 0 20 40 60 80 VCC = 3.3V, CLK = 5MHz VCC = 5V, CLK = IDLE VCC = 3.3V, CLK = IDLE VCC = 5V, CLK = 5MHz
3.5
100 120
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (C)
TEMPERATURE (C)
OUTPUT VOLTAGE vs. TEMPERATURE (OUTPUT LOW)
IOUT = 4mA 12 OUTPUT VOLTAGE (V) 10 8 6 4 2 0 -40 -20 0 20 40 60 80 100 120 VBB = 8V VBB = 76V VBB = 40V
MAX6921/31 toc06
OUTPUT RISE AND FALL WAVEFORM
MAX6921/31 toc07
14
BLANK 2V/div
OUT_ 20V/div
1s/div
TEMPERATURE (C)
Pin Description
PIN TSSOP MAX6921 1-5 6 7 8 9 MAX6931 1-5 6 7 8 -- WIDE SO/PLCC MAX6921 -- 27 28 1 2 OUT4 to OUT0 DIN VCC VBB DOUT VFD Anode and Grid Drivers. OUT4 to OUT0 are push-pull outputs swinging from VBB to GND (MAX6921 only), and from VBB to VSS (MAX6931 only). Serial-Data Input. Data is loaded into the internal shift register on CLK's rising edge. Logic Supply Voltage. Bypass to GND with 100nF capacitor. VFD Tube Supply Voltage. Bypass to GND with 100nF capacitor. Serial-Clock Output. Data is clocked out of the internal shift register to DOUT on CLK's rising edge. NAME FUNCTION
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
Pin Description (continued)
PIN TSSOP MAX6921 -- 10-19 -- MAX6931 9 10-19 -- WIDE SO/PLCC MAX6921 -- -- 3-12 VSS Filament Bias Supply Voltage. Bypass to GND with a 100nF capacitor. OUT19 to VFD Anode and Grid Drivers. OUT19 to OUT10 are push-pull outputs swinging from OUT10 VBB to GND (MAX6921 only), and from VBB to VSS (MAX6931 only). OUT19 to VFD Anode and Grid Drivers. OUT19 to OUT10 are push-pull outputs swinging from OUT10 VBB to GND. BLANK GND CLK LOAD OUT9 to OUT5 OUT9 to OUT0 Blanking Input. High forces outputs OUT0 to OUT19 low, without altering the contents of the output latches. Low enables outputs OUT0 to OUT19 to follow the state of the output latches. Ground Serial-Clock Input. Data is loaded into the internal shift register on CLK's rising edge. Load Input. Data is loaded transparently from the internal shift register to the output latch while LOAD is high. Data is latched into the output latch on LOAD's rising edge, and retained while LOAD is low. VFD Anode and Grid Drivers. OUT9 to OUT5 are push-pull outputs swinging from VBB to GND (MAX6921 only), and from VBB to VSS (MAX6931 only). VFD Anode and Grid Drivers. OUT9 to OUT0 are push-pull outputs swinging from VBB to GND. NAME FUNCTION
20 21 22 23
20 21 22 23
13 14 15 16
24-28 --
24-28 --
-- 17-26
CLK MAX6921 ONLY DIN SERIAL-TO-PARALLEL SHIFT REGISTER DOUT
LOAD
LATCHES
BLANK
MAX6921 MAX6931
OUT0 OUT1 OUT2
OUT19
Figure 1. MAX6921/MAX6931 Functional Diagram
6 _______________________________________________________________________________________
20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
VBB VBB
40 TYPICAL SLEW-RATE CONTROL 750 TYPICAL OUT_ SLEW-RATE CONTROL
40 TYPICAL OUT_ 750 TYPICAL
VSS
Figure 2. MAX6921 CMOS Output Driver Structure
Figure 3. MAX6931 CMOS Output Driver Structure
Detailed Description
The MAX6921/MAX6931 are VFD tube drivers comprising a 4-wire serial interface driving 20 high-voltage railto-rail output ports. The driver is suitable for both static and multiplexed displays. The output ports feature high current-sourcing capability to drive current into grids and anodes of static or multiplex VFDs. The ports also have active current sinking for fast discharge of capacitive display electrodes in multiplexing applications. The 4-wire serial interface comprises a 20-bit shift register and a 20-bit transparent latch. The shift register is written through a clock input CLK and a data input DIN. For the MAX6921, 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 the shift register outputs when LOAD is high, and latches the current state on the falling edge of LOAD. Each driver output is a slew-rated controlled CMOS push-pull switch driving between V BB and GND (MAX6921) or VSS (MAX6931). The output rise time is always slower than the output fall time to avoid shootthrough currents during output transitions. The output slew rates are slow enough to minimize EMI, yet are fast enough so as not to impact the typical 100s digit multiplex period and affect the display intensity.
4-Wire Serial Interface
The MAX6921/MAX6931 use 4-wire serial interface with three inputs (DIN, CLK, LOAD) and a data output (DOUT, MAX6921 only). This interface is used to write output data to the MAX6921/MAX6931 (Figure 4) (Table 1). The serial interface data word length is 20 bits, D0-D19. The functions of the four serial interface pins are: * CLK input is the interface clock, which shifts data into the MAX6921/MAX6931s' 20-bit shift register on its rising edge. * LOAD input passes data from the MAX6921/ MAX6931s' 20-bit shift register to the 20-bit output latch when LOAD is high (transparent latch), and latches the data on LOAD's falling edge * DIN is the interface data input, and must be stable when it is sampled on the rising edge of CLK. * DOUT is the interface data output, which shifts data out from the MAX6921's 20-bit shift register on the rising edge of CLK. Data at DIN is propagated through the shift register and appears at DOUT (20 CLK cycles + tDO) later. A fifth input, BLANK, can be taken high to force outputs OUT0 to OUT19 low, without altering the contents of the output latches. When the BLANK input is low, outputs OUT0 to OUT19 follow the state of the output latches. A common use of the BLANK input is PWM intensity control. The BLANK input's function is independent of the operation of the serial interface. Data can be shifted into the serial interface shift register and latched regardless of the state of BLANK.
Initial Power-Up and Operation
An internal reset circuit clears the internal registers of the MAX6921/MAX6931 on power-up. All outputs OUT0 to OUT19 and the interface output DOUT (MAX6921 only) initialize low regardless of the initial logic levels of the CLK, DIN, BLANK, and LOAD inputs.
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7
20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
tCSW LOAD tCL tCH tCSH tCP
CLK tDH tDS DIN D19 D18 D1 D0
tDO DOUT D19
Figure 4. 4-Wire Serial Interface Timing Diagram
Table 1. 4-Wire Serial Interface Truth Table
BLANKING SERIAL CLOCK SHIFT REGISTER CONTENTS LOAD LATCH CONTENTS OUTPUT CONTENTS INPUT INPUT DATA INPUT INPUT CLK D0 D1 D2 ... Dn-1 Dn LOAD D0 D1 D2 ... Dn-1 Dn BLANK D0 D1 D2 ... Dn-1 Dn DIN H L X H L R0 X P0 R0 R1 ... Rn-2 Rn-1 R0 R1 ... Rn-2 Rn-1 R1 R2 ... Rn-1 X P1 X ... X P2 ... Pn-1 Rn X Pn L H R0 R1 R2 P0 X P1 X P2 X ... Rn-1 Rn ... Pn-1 Pn ... X X L H P0 L P1 P2 L L ... ... Pn-1 L Pn L
L = Low logic level. H = High logic level. X = Don't care. P = Present state (shift register). R = Previous state (latched).
Writing Device Registers Using the 4-Wire Serial Interface
The MAX6921/MAX6931 are normally written using the following sequence: 1) Take CLK low. 2) Clock 20 bits of data in order D19 first to D0 last into DIN, observing the data setup and hold times. 3) Load the 20 output latches with a falling edge on LOAD. LOAD can be high or low during a transmission. If LOAD is high, then the data shifted into the shift register at DIN appear at the OUT0 to OUT19 outputs.
CLK and DIN can be used to transmit data to other peripherals. Activity on CLK always shifts data into the MAX6921/MAX6931s' shift register. However, the MAX6921/MAX6931 only update their output latch on the rising edge of LOAD, and the last 20 bits of data are loaded. Therefore, multiple devices can share CLK and DIN, as long as they have unique LOAD controls.
Determining Driver Output Voltage Drop
The outputs are CMOS drivers, and have a resistive characteristic. The typical and maximum sink and source output resistances can be calculated from the VH and VL electrical characteristics. Use this calculated resistance to determine the output voltage drop at different output currents.
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers
Output Current Ratings
The continuous current-source capability is 40mA per output. Outputs can drive up to 75mA as a repetitive peak current, subject to the on-time (output high) being no longer than 1ms, and the duty cycle being such that the output power dissipation is no more than the dissipation for the continuous case. The repetitive peak rating allows outputs to drive a higher current in multiplex grid driver applications, where only one grid is on at a time, and the multiplex time per grid is no more than 1ms. Since dissipation is proportional to current squared, the maximum current that can be delivered for a given multiplex ratio is given by: IPEAK = (grids x 1600)1/2 mA where grids is the number of grids in a multiplexed display. This means that a duplex application (two grids) can use a repetitive peak current of 56.5mA, a triplex (three grids) application can use a repetitive peak current of 69.2mA, and higher multiplex ratios are limited to 75mA. of the resistor can be determined by the load capacitance and timing characteristics required. Resistor R discharges tube capacitance C to 10% of the initial voltage in 2.3 x RC seconds. So, for example, a 15k value for R discharges 100pF tube grid or anode from 40V to 4V in 3.5s, but draws an additional 2.7mA from the driver when either output is high.
MAX6921/MAX6931
Power Dissipation
Take care to ensure that the maximum package dissipation ratings for the chosen package are not exceeded. Over-dissipation is unlikely to be an issue when driving static tubes, but the peak currents are usually higher for multiplexed tubes. When using multiple driver devices, try to share the average dissipation evenly between the drivers. Determine the power dissipation (P D ) for the MAX6921/MAX6931 for static tube drivers with the following equation: PD = (VCC x ICC) + (VBB x IBB) + ((VBB - VH) x IANODE x A) where: A = number of anodes driven (the MAX6921/MAX6931 can drive a maximum of 20). IANODE = maximum anode current. (VBB - VH) is the output voltage drop at the given maximum anode current IOUT. A static tube dissipation example follows: VCC = 5V 5%, VBB = 10V to 18V, A = 20, IOUT = 2mA PD = (5.25V x 1mA)+ (18V x 1.4mA) + ((2.5V x 2mA/25mA) x 2mA x 20) = 38mW Determine the power dissipation (PD) for the MAX6921/ MAX6931 for multiplex tube drivers with the following equation: PD = (VCC x ICC) + (VBB x IBB) + ((VBB - VH) x IANODE x A) + ((VBB - VH) x IGRID) where: A = number of anodes driven. G = number of grids driven. IANODE = maximum anode current. IGRID = maximum grid current. The calculation presumes all anodes are on, but only one grid is on. The calculated PD is the worst case, presuming one digit is always being driven with all its anodes lit. Actual PD can be estimated by multiplying this PD figure by the actual tube drive duty cycle, taking into account interdigit blanking and any PWM intensity control.
9
Paralleling Outputs
Any number of outputs within the same package can be paralleled in order to raise the current drive or reduce the output resistance. Only parallel outputs directly (by shorting outputs together) if the interface control can be guaranteed to set the outputs to the same level. Although the sink output is relatively weak (typically 750), that resistance is low enough to dissipate 530mW when shorted to an opposite level output at a VBB voltage of only 20V. A safe way to parallel outputs is to use diodes to prevent the outputs from sinking current (Figure 5). Because the outputs cannot sink current from the VFD tube, an external discharge resistor, R, is required. For static tubes, R can be a large value such as 100k. For multiplexed tubes, the value
MAX6921 MAX6931
OUT0
D1 OUTPUT D2
OUT1 R
Figure 5. Paralleling Outputs
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
A multiplexed tube dissipation example follows: VCC = 5V 5%, VBB = 36V to 42V, A = 12, G = 8, IANODE = 0.4mA, IGRID = 24mA PD = (5.25V x 1mA)+ (42V x 1.4mA) + ((2.5V x 0.4mA/25mA) x 0.4mA x 12) + ((2.5V x 24mA/25mA) x 24mA) = 122mW Thus, for a 28-pin wide TSSOP package (TJA = 1 / 0.0128 = 78.125C/W from Absolute Maximum Ratings), the maximum allowed ambient temperature TA is given by: TJ(MAX) = TA + (PD x TJA) = 150C = TA + (0.122 x 78.125C/W) So TA = +140.5C. This means that the driver can be operated in this application up to the MAX6921/MAX6931s' +125C maximum operating temperature.
DIN
Typical Application Circuit
MAX685x
VFDOUT VFCLK VFLOAD VFBLANK DIN CLK
MAX6921
LOAD BLANK DOUT
MAX6921
VFD TUBE DOUT DOUT
Power-Supply Considerations
The MAX6921/MAX6931 operate with multiple powersupply voltages. Bypass the V CC , V BB , and V SS (MAX6931 only) power-supply pins to GND with 0.1F capacitors close to the device. The MAX6931 can be operated with VSS connected to GND if a negative bias supply is not required. For multiplex applications, it may be necessary to add an additional bulk electrolytic capacitor of 1F or greater to the VBB supply.
CLK LOAD BLANK
MAX6921
DIN CLK LOAD BLANK
Power-Supply Sequencing
The order of the power-supply sequencing is not important. The MAX6921/MAX6931 will not be damaged if any combination of VCC, VBB, and VSS (MAX6931 only) is grounded while the other supply or supplies are maintained up to their maximum ratings. However, as with any CMOS device, do not drive the MAX6921/ MAX6931s' logic inputs if the logic supply VCC is not operational because the input protection diodes clamp the signals.
Cascading Drivers (MAX6921 Only)
Multiple MAX6921s can be cascaded, as shown in the Typical Application Circuit, by connecting each driver's DOUT to DIN of the next drivers. Devices can be cascaded at the full 5MHz CLK speed when VCC 4.5V. When VCC <4.5V, the longer propagation delay (tDO) limits the maximum cascaded CLK to 4MHz.
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers
Pin Configurations
TOP VIEW
VBB 1 DOUT 2 OUT19 3 OUT18 4 OUT17 5 OUT16 6 OUT15 7 OUT14 8 OUT13 9 OUT12 10 OUT11 11 OUT10 12 BLANK 13 GND 14 28 VCC 27 DIN 26 OUT0 25 OUT1 24 OUT2 OUT4 1 OUT3 2 OUT2 3 OUT1 4 OUT0 5 DIN 6 VCC 7 VBB 8 DOUT 9 OUT19 10 OUT18 11 OUT17 12 OUT16 13 OUT15 14 28 OUT5 27 OUT6 26 OUT7 25 OUT8 24 OUT9 OUT4 1 OUT3 2 OUT2 3 OUT1 4 OUT0 5 DIN 6 VCC 7 VBB 8 VSS 9 OUT19 10 OUT18 11 OUT17 12 OUT16 13 OUT15 14 28 OUT5 27 OUT6 26 OUT7 25 OUT8 24 OUT9
MAX6921/MAX6931
MAX6921AWI
MAX6921AUI
23 OUT3 22 OUT4 21 OUT5 20 OUT6 19 OUT7 18 OUT8 17 OUT9 16 LOAD 15 CLK
23 LOAD 22 CLK 21 GND 20 BLANK 19 OUT10 18 OUT11 17 OUT12 16 OUT13 15 OUT14
MAX6931AUI
23 LOAD 22 CLK 21 GND 20 BLANK 19 OUT10 18 OUT11 17 OUT12 16 OUT13 15 OUT14
OUT18
OUT19
WIDE SO
TSSOP
DOUT OUT0 VCC DIN VBB
TSSOP
4
3
2
1
28
27
26
OUT17 OUT16 OUT15 OUT14 OUT13
5 6 7 8 9
25 24 23
OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7
MAX6921AQI
22 21 20 19
OUT12 10 OUT11 11 12 OUT10 13 BLANK 14 GND 15 CLK 16 LOAD 17 OUT9 18 OUT8
PLCC
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers MAX6921/MAX6931
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE 28 TSSOP 28 Wide SO 28 PLCC PACKAGE CODE U28+1 W28+1 Q28+1 DOCUMENT NO. 21-0066 21-0042 21-0049
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20-Output, 76V, Serial-Interfaced VFD Tube Drivers
Revision History
REVISION NUMBER 0 1 REVISION DATE 10/03 4/10 Initial release Added automotive and lead-free parts to Ordering Information DESCRIPTION PAGES CHANGED -- 1
MAX6921/MAX6931
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
(c) 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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