LM3532TMX-40ANOPB National Semiconductor Corporation, LM3532TMX-40ANOPB Datasheet - Page 14

• Manufacturer Part Number: LM3532TMX-40ANOPB
• Description: High Efficiency White Led Driver With Programmable Ambient Light Sensing Capability And I2c-compatible Interface
• Manufacturer: National Semiconductor Corporation

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LED CURRENT RAMPING
The LM3532 provides 4 methods to control the rate of rise or
fall of the LED current during these events:
1.
2.
3.
4.
See
STARTUP AND SHUTDOWN CURRENT RAMPING
The startup and shutdown ramp rates are independently pro-
grammable in the startup/Shutdown Ramp Rate Register
(see
shutdown ramp rates. The startup ramp rates are indepen-
dently programmable from the shutdown ramp rates, but not
independently programmable for each Control Bank. For ex-
ample, programming a startup or shutdown ramp rate, pro-
grams the same ramp rate for each Control Bank.
RUN TIME RAMP RATES
Current ramping from one brightness level to the next is pro-
grammed via the Run Time Ramp Rate Register (see
5). There are 8 different ramp-up and 8 different ramp-down
rates. The ramp-up rate is independently programmable from
the ramp-down rate, but not independently programmable for
each Control Bank. For example, programming a ramp-up or
Startup from 0 to the initial target
Shutdown
Ramp up from one brightness level to the next
Ramp down from one brightness level to the next
Table 4
Table
4). There are 8 different startup and 8 different
and
Table
5.
FIGURE 3. Exponential Mapping Response
Table
14
a ramp-down rate programs the same rate for each Control
Bank.
LED CURRENT MAPPING MODES
All LED current brightness codes are 8 bits (256 different lev-
els), where each bit represents a percentage of the pro-
grammed full-scale current setting for that particular Control
Bank. The percentage of the full-scale current is different de-
pending on which mapping mode is selected. The mapping
mode can be either exponential or linear. Mapping mode is
selected via bit [1] of the Control A, B, or C Brightness Con-
figuration Registers.
EXPONENTIAL CURRENT MAPPING MODE
In exponential mapping mode, the backlight code to LED cur-
rent approximates the following equation:
where Code is the 8-bit code in the programmed brightness
register and D
assigned to the particular control bank. For the exponential
mapped mode
scale current setting vs 8-bit brightness code.
PWM
(Figure
is the duty cycle of the PWM input that is
3) shows the typical response of % full-
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