STFPC311 datasheet(29/39 Pages) STMICROELECTRONICS

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STFPC311

10 Maximum rating

29/39

10.1

Power consumption estimation

The maximum power consumption is comprised of the Vacuum Florescent Display (VFD) driver

dissipation, Load Resistance (RL), LED driver dissipation, and dynamic power consumption.

PMAX = VFD + RL + LED + PDYN

Where,

●

PMAX = maximum power consumption,

●

VFD = Vacuum Florescent Display driver dissipation,

●

RL = load resistance,

●

LED = LED driver dissipation, and

●

PDYN = dynamic power consumption.

If the segment current (ISEG) = 3mA, grid current (IGRID) = 15mA, and the LED current =

20mA, then:

FIP = (#segments x 6) + [#grids/(#grids +1)] x 30mW,

RL dissipation = (VDD – VSS)2 ÷ 50(segment + 1mW),

LED driver dissipation = #LEDs x 20mW, and

PDYN = VDD x 5mW.

To finish this example:

FIP driver dissipation = 16 x 6 + 12/13 x 30 = 124mW

RL dissipation = 33.32/50 x 17 = 377mW

LED driver dissipation = 2 x 20 = 40

PDYN = 3.3 x 5 = 16.5mW

The maximum power consumption (Total) = 557.5mW

Where,

VSS = –30V,

VDD = 3.3V, and the application is in 16-segment, 12-digit mode.

STFPC311 Datasheet(PDF) 29 Page - STMicroelectronics