LP5569ARTWR datasheet(29/93 Pages) TI2

29 / 93 page

DIMMING

CONTROL

STEP COUNT

STEP TIME

SPAN =

187.5 ms

TIME ELAPSED (ms)

375

750

1125

1500

140

141

142

143

144

145

146

147

148

RAMP

INSTRUCTION

LP5569

www.ti.com

SNVSAP8A – JULY 2017 – REVISED SEPTEMBER 2017

Product Folder Links: LP5569

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(1)

Compatible with LP5523 and LP55231

Programming ramps with variables is very similar to programming ramps with numerical operands. The only

difference is that step time and number of increments are captured from variable registers when the instruction

execution is started. If the variables are updated after starting the instruction execution, it has no effect on

instruction execution. Again, at each ramp step the output is incremented or decremented by 1 unless the step

time is 0 or the number of increments is 0. The time span for one step is defined with the prescale and step-time

bits. The step time is defined with variable A, B, C, or D. Variable A is set by an I2C write to the engine 1, 2, or 3

variable A register or the ld instruction, variables B and C are set with the ld instruction, and variable D is set by

an I2C write to the variable D register.

Setting the EXP_EN bit of registers 07h–0Fh high or low sets the exponential (1) or linear ramp (0). By using the

exponential ramp setting, the visual effect appears like a linear ramp to the human eye.

Table 9. Ramp Instructions

INST.

Bit

[15]

Bit

[14]

Bit

[13]

Bit

[12]

Bit

[11]

Bit

[10]

Bit

[9]

Bit

[8]

Bit

[7]

Bit

[6]

Bit

[5]

Bit

[4]

Bit

[3]

Bit

[2]

Bit

[1]

Bit

[0]

ramp(1)

pre-

scale

step time

sign

no. of increments

ramp(1)

pre-

scale

sign

step-time

variable

no.-of-

increments

variable

PARAMETER

NAME

NUMERIC OR

VARIABLE

VALUE (d)

DESCRIPTION

prescale

Numeric

32.7 kHz / 16

≥ 0.488 ms cycle time

32.7 kHz / 512

≥ 15.625 ms cycle time

sign

Numeric

Increase PWM output

Decrease PWM output

step time

Numeric

1–31

One ramp increment done is in step time × prescale.

Value in the variable A, B, C, or D must be from 1 to 31 for correct

operation.

Variable

0–3

no. of

increments

Numeric

0–255

The number of ramp cycles. Variables A to D as input.

Variable

0–3

8.5.2.4.2

Ramp Instruction Application Example

An example of generating a 1.5-s ramp from PWM value 140 (approximately 55%) to 148 (approximately 58%).

The ramp instruction uses relative values, so in this example we must ramp 8 steps up, as shown in Figure 25.

The parameters for the RAMP instruction are:

•

Positive ramp

→ sign = 0 (increase by 1)

•

Step from 140 to 148

→ no. of increments = 8

•

Ramp time 1.5 s

→ 1.5 s / 8 steps = 187.5 ms/step

•

Prescale = 1

→ 15.625 ms cycle time

•

187.5 ms / 15.625 ms = 12

→ step time = 12

Figure 25. Example of Ramp Instruction

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