LM3528TMEV National Semiconductor, LM3528TMEV Datasheet - Page 21

• Manufacturer Part Number: LM3528TMEV
• Description: BOARD EVAL FOR LM3528 12MCRSMD
• Manufacturer: National Semiconductor

Specifications of LM3528TMEV

• Current - Output / Channel: 20mA
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 21V
• Features: Dimmable, I²C Interface
• Voltage - Input: 2.5 ~ 5.5V
• Utilized Ic / Part: LM3528
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

BRIGHTNESS RATE OF CHANGE DESCRIPTION
RMP0 and RMP1 control the rate of change of the LED cur-
rent I
or BSUB. There are 4 user programmable LED current rates
of change settings for the LM3528 (see Table 5).
TABLE 5. Rate of Change Bits
For example, if R
the contents of BMAIN set to 0x7F (I
the contents of BMAIN are changed to 0x00 resulting in
(I
I
elapsing between steps, excluding the step from 0x7F to
0x7E, resulting in a full scale current change in 1638ms. The
total time to transition from one brightness code to another is:
The following 3 additional examples detail possible scenarios
when using the brightness register in conjunction with the rate
of change bits and the enable bits.
Example 1:
Step 1: Write to BMAIN a value corresponding to I
mA.
MAIN
MAIN
MAIN
will change from 20mA to 0mA in 127 steps with 13ms
= 0mA). With RMP0 =1 and RMP1 = 1 (13ms/step),
RMP0
0
0
1
1
and I
SUB/FB
SET
in response to changes in BMAIN and/
= 12.1kΩ then I
RMP1
0
1
0
1
MAIN
LED_MAX
FIGURE 9. I
Change Rate
(t
12.75µs/step
3.25ms/step
6.5ms/step
13ms/step
= 20mA), suppose
STEP
= 20mA. With
)
MAIN
MAIN
= 20-
or I
SUB
21
vs BMAIN or BSUB Data
Step 2: Write 1 to ENM (turning on MAIN)
Step 3: I
RMP1. (RMP0 and RMP1 bits set the duration spent at one
brightness code before incrementing to the next).
Step 4: ENM is set to 0 before 20mA is reached, thus the LED
current fades off at a rate given by RMP0 and RMP1 without
I
Example 2:
Step 1: ENM is 1, and BMAIN has been programmed with
code 0x01. This results in a small current into MAIN.
Step 2: BMAIN is programmed with 0x7F (full scale current).
This causes I
ed by RMP0 and RMP1.
Step 3: Before I
with 0x30. I
Step 4: When I
down to the current corresponding to 0x30 at a rate set by
RMP0 and RMP1.
Example 3:
Step 1: Write to BMAIN a value corresponding to I
mA.
Step 2: Write a 1 to both RMP0 and RMP1.
Step 3: Write 1 to ENM (turning on MAIN).
Step 4: I
RMP1. (RMP0 and RMP1 bits set the duration spent at one
brightness code before incrementing to the next).
Step 5: After 1.222s I
I
RMP0 and RMP1 are both programmed with 0.
Step 6: I
at a new ramp rate of 12.75µs/step.
MAIN
LED_MAX
going up to 20mA.
MAIN
MAIN
MAIN
(0.19687 × 20mA = 3.9374mA). Simultaneously,
MAIN
ramps toward 20mA with a rate set by RMP0 and
continues ramping from 3.9374mA to 20mA, but
MAIN
ramps to 20mA with a rate set by RMP0 and
MAIN
MAIN
will continue to ramp to full scale.
to ramp toward full-scale at the rate select-
reaches full-scale BMAIN is programmed
has reached full-scale value it will ramp
MAIN
has ramped to 19.687% of
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MAIN
= 20-