MAX6921AQI(2003) 查看數據表（PDF） - Maxim Integrated

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MAX6921AQI
(Rev.:2003)

20-Output, 76V, Serial-Interfaced VFD Tube Drivers

Maxim Integrated 

20-Output, 76V, Serial-Interfaced

VFD Tube Drivers

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)

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.

Power-Supply Considerations

The MAX6921/MAX6931 operate with multiple power-

supply voltages. Bypass the VCC, VBB, and VSS

(MAX6931 only) power-supply pins to GND with 0.1µF

capacitors close to the device. The MAX6931 may be

operated with VSS tied to GND if a negative bias supply

is not required. For multiplex applications, it may be

necessary to add an additional bulk electrolytic capaci-

tor of 1µF or greater to the VBB supply.

Power-Supply Sequencing

The order of the power-supply sequencing is not impor-

tant. 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 may be cascaded, as shown in the

Typical Application Circuit, by connecting each driver’s

DOUT to DIN of the next drivers. Devices may be cas-

caded 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.

Typical Application Circuit

MAX685x

VFDOUT

VFCLK

VFLOAD

VFBLANK

MAX6921

DIN

CLK

LOAD

BLANK

DOUT

MAX6921

DIN

CLK

LOAD

BLANK

DOUT

MAX6921

DIN

CLK

LOAD

BLANK

DOUT

Chip Information

TRANSISTOR COUNT: 2743

PROCESS: BiCMOS

10 ______________________________________________________________________________________

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