BUF01900 Datasheet, PDF(15/25 Page) Texas Instruments – Programmable Voltage Source with Memory

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BUF01900 Datasheet, PDF (15/25 Pages) Texas Instruments – Programmable Voltage Source with Memory

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EXTERNAL VOLTAGE DIVIDER RESISTOR

SELECTION

The external resistive voltage-divider consisting of R1 and

R2 (see Figure 16, Figure 17, and Figure 18) sets both the

maximum value of the VCOM adjustment range and the ini-

tial VCOM voltage. Follow the steps below to calculate the

correct values for R1 and R2

Step 1: Choose the supply voltage, (VS)

Step 2: Set the nominal VCOM voltage. This voltage is the

VCOM voltage at which the unadjusted panel should be at

power-on. The default power-up DAC code is midscale.

Step 3: Choose the VCOM adjustment range. The adjust-

ment range is the difference between the lowest and the

highest desired VCOM voltage. If the default power-up code

is not overwritten by software at the beginning of the ad-

justment cycle, the adjustment range is symmetrical

around the chosen nominal VCOM voltage.

Step 4: Calculate the resistors based on the following for-

mulas or simply download the Microsoft Excelï£ª calculator

located in the product folder of BUF0190x available at

www.ti.com.

250kW @ Adj_range

VCOM * 0.5 @ (Adj_range)

(1)

Ç Ç R2 + VS

VCOM

) 1

500kW

250kW

(2)

BUF01900

BUF01901

SBOS337A â OCTOBER 2006 â REVISED OCTOBER 2006

DESIGN EXAMPLE

Step 1: Supply Voltage is 10V.

Step 2: Nominal VCOM is determined to be 4V.

Step 3: The desired total adjustment range is 1V. In the

case of using the default power-up DAC code (midscale),

the adjustment range for the VCOM voltage will be from

3.5V to 4.5V.

Step 4: Calculation of R1 and R2

R1 = 71.4kâ¦ => choose closest 1% resistor (71.5kâ¦)

R2 = 45.5kâ¦ => choose closest 1% resistor (45.3kâ¦)

Step 5: Appropriate number of adjustment steps between

code 00h and code 3FFh is determined to be 32. This value

leads to a step size of 32 codes between adjustment

points, which translates into approximately 31mV voltage

difference between steps.

MOTOR DRIVE CIRCUIT

The BUF01900 can be used to drive small motors directly

because of the large output drive capability (> 100mA), as

illustrated in Figure 23.

VSD

15V

CALCULATING THE VCOM OUTPUT VOLTAGE

With R1 and R2 properly set, VBIAS or VCOM output voltage

can be calculated for any digital code with the following for-

mula:

V COM

250kW

@ R2 @ VS ) R1 @ R2 @ VS (CodeÅ1023)

R1 @ R2 ) 250kW @ ÇR1 ) R2Ç

(3)

10kâ¦

ÂµC

VCOM

BUF01900

CALCULATING THE ADJUSTMENT

RESOLUTION

The resolution of the adjustment is a function of the step

size. The resolution can be calculated by simply dividing

the chosen adjustment range by the number of steps:

Resolution = Adj_range/steps (example: 32 steps be-

tween code 0h and code 3FFh)

Figure 23. Motor Drive Circuit

▷