LP5523 datasheet(39/56 Pages) TI1

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DIMMING

CONTROL

STEP COUNT

STEP TIME

SPAN =

187.5ms

TIME ELAPSED (ms)

375

750

1125

1500

140

141

142

143

144

145

146

147

148

RAMP INSTRUCTION

LP5523

www.ti.com

SNVS550D – SEPTEMBER 2009 – REVISED MAY 2013

Name

Value (d)

Description

Divides master clock (32.7 kHz) by 16 = 2048 Hz -> 0.488 ms cycle time

prescale

Divides master clock (32.7 kHz) by 512 = 64 Hz -> 15.625 ms cycle time

Increase PWM output

sign

Decrease PWM output

step time(1)

1 - 31

One ramp increment done in (step time) x (prescale).

# of

The number of increment/decrement cycles. Note: Value 0 takes the same time as increment by 1, but

0 - 255

increments(1)

it is the wait instruction.

One ramp increment done in (step time) x (prescale).

Step time is loaded with the value (5 LSB bits) of the variable defined below.

0 = local variable A

step time(2)

0 - 3

1 = local variable B

2 = global variable C

3 = register address 3CH variable D value, or register address 42H value.

The value of the variable should be from 00001b to 11111b (1d to 31d) for correct operation.

The number of increment/decrement cycles. Value is taken from variable defined below:

0 = local variable A

# of

0 - 3

1 = local variable B

increments(2)

2 = global variable C

3 = register address 3CH variable D value, or register address 42H value.

(1)

Valid for numerical operands.

(2)

Valid for variables.

Ramp Instruction Application Example

Suppose that the LED dimming is controlled according to the linear scale and effective PWM value at the

moment t=0 is 140d (~55%,), as shown in the figure below, and we want to reach a PWM value of 148d (~58%)

at the moment t = 1.5s. The parameters for the RAMP instruction will be:

•

Prescale = 1

→ 15.625 ms cycle time

•

Step time = 12

→ step time span will be 12*15.625 ms = 187.5 ms

•

Sign = 0

→ increase PWM output

•

# of increments = 8

→ take 8 steps

Figure 26. Example of Ramp Instruction

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