19-3020; Rev 1; 4/10 20-Output, 76V, Serial-Interfaced VFD Tube Drivers 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 -40°C to +125°C Temperature Range Ordering Information PART TEMP RANGE MAX6921AUI+ -40°C to +125°C 28 TSSOP MAX6921AWI/V+ -40°C to +125°C 28 Wide SO MAX6921AQI+ -40°C to +125°C 28 PLCC MAX6931AUI+ -40°C to +125°C 28 TSSOP +Denotes a lead-free(Pb)/RoHS-compliant package. /V denotes an automotive qualified part. Typical Operating Circuit Applications White Goods Industrial Weighing Gaming Machines Security Automotive Telecom Avionics VFD Modules Instrumentation Industrial Control PIN-PACKAGE +5V +60V C2 100nF C1 100nF 7 VCC 8 VBB MAX6931 VFDOUT VFCLK VFLOAD VFBLANK 6 22 23 20 20 DIN OUT0–OUT19 CLK VFD TUBE µC LOAD BLANK VSS -7V 9 GND 21 C3 100nF Pin Configurations appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products 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. 1 MAX6921/MAX6931 General Description MAX6921/MAX6931 20-Output, 76V, Serial-Interfaced VFD Tube Drivers 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 = +70°C) 28-Pin TSSOP (derate 12.8mW/°C over +70°C)................................................................1025mW 28-Pin Wide SO (derate 12.5mW/°C over +70°C)................................................................1000mW 28-Pin PLCC (derate 10.5mW/°C over +70°C)..................................................................842mW Operating Temperature Range (TMIN to TMAX) ...............................................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) Wide SO, TSSOP lead(Pb)-free ...................................+260°C PLCC lead(Pb)-free......................................................+245°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. 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) MAX UNITS Logic Supply Voltage PARAMETER VCC 3 5.5 V Tube Supply Voltage VBB 8 76 V Bias Supply Voltage (MAX6931 Only) VSS -11 0 V Total Supply Voltage (MAX6931 Only) VBB - VSS 76 V Logic Supply Operating Current SYMBOL ICC CONDITIONS 78 All outputs OUT_ high, TA = +25°C CLK = idle TA = -40°C to +125°C 540 IBB All outputs OUT_ high All outputs OUT_ low Bias Supply Operating Current (MAX6931 Only) ISS All outputs OUT_ high 2 TYP All outputs OUT_ low, TA = +25°C CLK = idle TA = -40°C to +125°C All outputs OUT_ low Tube Supply Operating Current MIN 170 200 900 µA 1000 TA = +25°C 1.65 3.0 0.85 1.3 TA = -40°C to +125°C 6.9 TA = +25°C TA = -40°C to +125°C mA 1.4 TA = +25°C -0.8 TA = -40°C to +125°C -1.9 TA = +25°C -1.4 TA = -40°C to +125°C -1.5 -0.38 -0.87 _______________________________________________________________________________________ mA 20-Output, 76V, Serial-Interfaced VFD Tube Drivers (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 CONDITIONS VBB ≥ 15V IOUT = -25mA VBB ≥ 15V IOUT = -40mA High-Voltage OUT_ 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 MIN TYP TA = +25°C VBB - 2 TA = -40°C to +85°C VBB - 2.5 MAX UNITS TA = -40°C to +125°C TA = -40°C to +85°C VBB - 3.5 TA = -40°C to +125°C VBB - 4.0 TA = +25°C V VBB - 1.2 TA = -40°C to +85°C VBB - 2.5 TA = -40°C to +125°C VBB - 3.0 TA = +25°C 0.75 1 TA = -40°C to +85°C 1.5 TA = -40°C to +125°C 1.9 TA = +25°C 0.8 1.1 TA = -40°C to +85°C 1.6 TA = -40°C to +125°C 2.0 TA = +25°C V VSS + 0.75 VSS + 1 TA = -40°C to +85°C VSS + 1.5 TA = -40°C to +125°C VSS + 1.9 TA = +25°C VSS + 0.8 VSS + 1.1 TA = -40°C to +85°C VSS + 1.6 TA = -40°C to +125°C VSS + 2.0 V Rise Time OUT_ (20% to 80%) tR VBB = 60V, CL = 50pF, RL =2.3kΩ 0.9 2 µs Fall Time OUT_ (80% to 20%) tF VBB = 60V, CL = 50pF, RL =2.3kΩ 0.6 1.5 µs µs SERIAL INTERFACE TIMING CHARACTERISTICS LOAD Rising to OUT_ Falling Delay (Notes 2, 3) 0.9 1.8 LOAD Rising to OUT_ Rising Delay (Notes 2, 3) 1.2 2.4 µs BLANK Rising to OUT_ Falling Delay (Notes 2, 3) 0.9 1.8 µs BLANK Falling to OUT_ Rising Delay (Notes 2, 3) 1.3 2.5 µs 0.05 10 µA Input Leakage Current CLK, DIN, LOAD, BLANK IIH, IIL Logic-High Input Voltage CLK, DIN, LOAD, BLANK VIH Logic-Low Input Voltage CLK, DIN, LOAD, BLANK VIL Hysteresis Voltage DIN, CLK, LOAD, BLANK ∆VI High-Voltage DOUT VOH ISOURCE = -1.0mA Low-Voltage DOUT VOL ISINK = 1.0mA 0.5 0.8 x VCC V 0.3 x VCC 0.6 V V VCC 0.5 V 0.5 V _______________________________________________________________________________________ 3 MAX6921/MAX6931 ELECTRICAL CHARACTERISTICS (continued) 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 CONDITIONS CDOUT = 10pF (Note 2) Rise and Fall Time DOUT TYP MAX 3V to 4.5V MIN 60 100 4.5V to 5.5V 30 80 UNITS ns CLK Clock Period tCP 200 ns CLK Pulse-Width High tCH 90 ns 90 ns CLK Pulse-Width Low tCL CLK Rise to LOAD Rise Hold tCSH DIN Setup Time tDS DIN Hold Time tDH DOUT Propagation Delay tDO LOAD Pulse High (Note 2) 100 ns 5 ns 3.0V to 4.5V 20 4.5V to 5.5V 15 CDOUT = 10pF ns 3.0V to 4.5V 25 120 240 4.5V to 5.5V 20 75 150 tCSW ns 55 ns Note 1: All parameters are tested at TA = +25°C. 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 = +25°C, unless otherwise noted.) 1.4 1.2 VBB = 40V VBB = 8V 1.0 0.8 0.6 1.4 1.2 VBB = 76V 1.0 0.8 0.6 0.4 0.2 0.2 VBB = 40V VBB = 8V 0 20 40 60 TEMPERATURE (°C) 80 100 120 350 VCC = 5V, CLK = 5MHz 300 250 VCC = 3.3V, CLK = 5MHz 200 150 100 50 0 -40 -20 400 MAX6921/31 toc03 1.6 0.4 0 4 1.8 SUPPLY CURRENT (µA) 1.6 2.0 LOGIC SUPPLY CURRENT (ICC) vs. TEMPERATURE (OUTPUTS LOW) MAX6921/31 toc02 VBB = 76V 1.8 SUPPLY CURRENT (mA) 2.0 TUBE SUPPLY CURRENT (IBB) vs. TEMPERATURE (OUTPUTS HIGH) MAX6921/31 toc01 TUBE SUPPLY CURRENT (IBB) vs. TEMPERATURE (OUTPUTS LOW) SUPPLY CURRENT (mA) MAX6921/MAX6931 20-Output, 76V, Serial-Interfaced VFD Tube Drivers VCC = 5V, CLK = IDLE VCC = 3.3V, CLK = IDLE 0 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 120 -40 -20 0 20 40 60 TEMPERATURE (°C) _______________________________________________________________________________________ 80 100 120 20-Output, 76V, Serial-Interfaced VFD Tube Drivers LOGIC SUPPLY CURRENT (ICC) vs. TEMPERATURE (OUTPUTS HIGH) OUTPUT VOLTAGE (VBB - VH) vs. TEMPERATURE (OUTPUT HIGH) 650 600 VCC = 3.3V, CLK = 5MHz 550 VCC = 5V, CLK = IDLE 500 VBB = 8V 2.5 2.0 VBB = 40V 1.5 VBB = 76V 1.0 VCC = 3.3V, CLK = IDLE 0.5 450 400 0 -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) TEMPERATURE (°C) OUTPUT VOLTAGE vs. TEMPERATURE (OUTPUT LOW) OUTPUT RISE AND FALL WAVEFORM IOUT = 4mA 12 VBB = 76V 10 MAX6921/31 toc06 MAX6921/31 toc07 14 OUTPUT VOLTAGE (V) IOUT = -40mA 3.0 OUTPUT VOLTAGE (V) SUPPLY CURRENT (µA) 700 MAX6921/31 toc05 VCC = 5V, CLK = 5MHz 750 3.5 MAX6921/31 toc04 800 BLANK 2V/div VBB = 40V 8 6 OUT_ 20V/div VBB = 8V 4 2 0 -40 -20 0 20 40 60 80 100 120 1µs/div TEMPERATURE (°C) Pin Description PIN WIDE SO/PLCC TSSOP NAME FUNCTION 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. MAX6921 MAX6931 MAX6921 1–5 1–5 — 6 6 27 OUT4 to OUT0 DIN 7 7 28 VCC Logic Supply Voltage. Bypass to GND with 100nF capacitor. 8 8 1 VBB VFD Tube Supply Voltage. Bypass to GND with 100nF capacitor. 9 — 2 DOUT Serial-Clock Output. Data is clocked out of the internal shift register to DOUT on CLK’s rising edge. _______________________________________________________________________________________ 5 MAX6921/MAX6931 Typical Operating Characteristics (continued) (VCC = 5.0V, VBB = 76V, and TA = +25°C, unless otherwise noted.) MAX6921/MAX6931 20-Output, 76V, Serial-Interfaced VFD Tube Drivers Pin Description (continued) PIN WIDE SO/PLCC TSSOP MAX6921 MAX6931 MAX6921 — 9 — NAME VSS FUNCTION Filament Bias Supply Voltage. Bypass to GND with a 100nF capacitor. 10–19 10–19 — 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). — — 3-12 OUT19 to VFD Anode and Grid Drivers. OUT19 to OUT10 are push-pull outputs swinging from OUT10 VBB to GND. 20 20 13 BLANK 21 21 14 GND 22 22 15 CLK 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. 23 23 16 LOAD 24–28 24–28 — OUT9 to OUT5 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). — — 17-26 OUT9 to OUT0 VFD Anode and Grid Drivers. OUT9 to OUT0 are push-pull outputs swinging from VBB to GND. CLK MAX6921 ONLY SERIAL-TO-PARALLEL SHIFT REGISTER DIN DOUT LATCHES LOAD BLANK MAX6921 MAX6931 OUT0 OUT1 OUT2 OUT19 Figure 1. MAX6921/MAX6931 Functional Diagram 6 _______________________________________________________________________________________ 20-Output, 76V, Serial-Interfaced VFD Tube Drivers 40Ω TYPICAL 40Ω TYPICAL SLEW-RATE CONTROL OUT_ 750Ω TYPICAL SLEW-RATE CONTROL OUT_ 750Ω TYPICAL VSS Figure 2. MAX6921 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 100µs digit multiplex period and affect the display intensity. 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. Figure 3. MAX6931 CMOS Output Driver Structure 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. _______________________________________________________________________________________ 7 MAX6921/MAX6931 VBB VBB MAX6921/MAX6931 20-Output, 76V, Serial-Interfaced VFD Tube Drivers tCSW LOAD tCL tCSH tCH tCP CLK tDH tDS D19 DIN 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 H R0 R1 … Rn-2 Rn-1 L L R0 R1 … Rn-2 Rn-1 X R0 R1 R2 … Rn-1 X X X … X P0 P1 P2 … Pn-1 Rn X L R0 R1 R2 … Rn-1 Rn Pn H P0 P1 P2 … Pn-1 Pn L P0 X X X … H L X X P1 P2 L L … Pn-1 Pn … L 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. 8 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. _______________________________________________________________________________________ 20-Output, 76V, Serial-Interfaced VFD Tube Drivers 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. 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 750Ω), 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 100kΩ. For multiplexed tubes, the value 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 15kΩ value for R discharges 100pF tube grid or anode from 40V to 4V in 3.5µs, but draws an additional 2.7mA from the driver when either output is high. 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) MAX6921 MAX6931 D1 OUT0 OUTPUT D2 OUT1 R Figure 5. Paralleling Outputs 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 MAX6921/MAX6931 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 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 = 78.125°C/W from Absolute Maximum Ratings), the maximum allowed ambient temperature TA is given by: TJ(MAX) = TA + (PD x TJA) = 150°C = TA + (0.122 x 78.125°C/W) Typical Application Circuit MAX685x MAX6921 VFDOUT DIN VFCLK CLK VFLOAD LOAD VFBLANK BLANK DOUT So TA = +140.5°C. This means that the driver can be operated in this application up to the MAX6921/MAX6931s’ +125°C maximum operating temperature. MAX6921 DIN 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 0.1µF 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 1µF or greater to the VBB supply. CLK LOAD BLANK DOUT MAX6921 Power-Supply Sequencing DIN 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. CLK LOAD BLANK 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. 10 VFD TUBE MAX6921/MAX6931 20-Output, 76V, Serial-Interfaced VFD Tube Drivers ______________________________________________________________________________________ DOUT 20-Output, 76V, Serial-Interfaced VFD Tube Drivers TOP VIEW VBB 1 28 VCC OUT4 1 28 OUT5 OUT4 1 28 OUT5 DOUT 2 27 DIN OUT3 2 27 OUT6 OUT3 2 27 OUT6 26 OUT0 OUT2 3 26 OUT7 OUT2 3 26 OUT7 25 OUT1 OUT1 4 25 OUT8 OUT1 4 25 OUT8 24 OUT2 OUT0 5 24 OUT9 OUT0 5 23 OUT3 DIN 6 23 LOAD DIN 6 OUT15 7 22 OUT4 VCC 7 22 CLK VCC 7 22 CLK OUT14 8 21 OUT5 VBB 8 21 GND VBB 8 21 GND OUT13 9 20 OUT6 DOUT 9 20 BLANK VSS 9 20 BLANK OUT12 10 19 OUT7 OUT19 10 19 OUT10 OUT19 10 19 OUT10 OUT11 11 18 OUT8 OUT18 11 18 OUT11 OUT18 11 18 OUT11 OUT10 12 17 OUT9 OUT17 12 17 OUT12 OUT17 12 17 OUT12 BLANK 13 16 LOAD OUT16 13 16 OUT13 OUT16 13 16 OUT13 15 CLK OUT15 14 15 OUT14 OUT15 14 15 OUT14 VCC DIN OUT0 3 2 1 28 27 26 OUT17 5 25 OUT1 OUT16 6 24 OUT2 OUT15 7 23 OUT3 OUT14 8 22 OUT4 OUT13 MAX6921AQI 9 21 OUT5 OUT12 10 20 OUT6 OUT11 19 OUT7 15 16 17 18 OUT9 OUT8 14 LOAD 13 CLK 11 12 24 OUT9 MAX6931AUI 23 LOAD TSSOP VBB 4 TSSOP DOUT WIDE SO GND GND 14 MAX6921AUI OUT19 OUT16 6 MAX6921AWI OUT18 OUT17 5 OUT10 OUT18 4 BLANK OUT19 3 PLCC ______________________________________________________________________________________ 11 MAX6921/MAX6931 Pin Configurations MAX6921/MAX6931 20-Output, 76V, Serial-Interfaced VFD Tube Drivers Package Information Chip Information PROCESS: BiCMOS 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 12 PACKAGE CODE DOCUMENT NO. 28 TSSOP U28+1 21-0066 28 Wide SO W28+1 21-0042 28 PLCC Q28+1 21-0049 ______________________________________________________________________________________ 20-Output, 76V, Serial-Interfaced VFD Tube Drivers REVISION NUMBER REVISION DATE 0 10/03 Initial release — 1 4/10 Added automotive and lead-free parts to Ordering Information 1 DESCRIPTION PAGES CHANGED 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 © 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX6921/MAX6931 Revision History