LM3532TMX-40ANOPB National Semiconductor Corporation, LM3532TMX-40ANOPB Datasheet - Page 15

• 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

LINEAR CURRENT MAPPING
In linear mapping mode the backlight code to LED current
approximates the following equation:
LED CURRENT CONTROL
Once the Full-Scale Current is set, control of the LM3532’s
LED current can be done via 2 methods:
1.
2.
I
rent by writing directly to the specific brightness register. In
ambient light sensor current control the LED current is auto-
matically set by the ambient light sensor interface.
I
I
Target Registers (for the respective Control Bank) as the
brightness register. This is done via bits[4:2] of the Control (A,
B, or C) Brightness Registers (see
Table
A Brightness Register with (000) makes the brightness reg-
ister for Bank A (in I
Target 0 Register.
I
I
at one of the PWM inputs (PWM1 or PWM2). In this situation
2
2
2
2
2
C current control allows for the direct control of the LED cur-
C CURRENT CONTROL
C Current Control is accomplished by using one of the Zone
C CURRENT CONTROL WITH PWM
C Current Control can also incorporate the PWM duty cycle
I
Ambient Light Sensor Current Control
2
C Current Control
11). For example, programming bits[4:2] of the Control
2
C Current Control) the Control A Zone
Table
9,
FIGURE 4. Linear Mapping Response
Table
10, and
15
where Code is the 8-bit code in the programmed brightness
register and DPWM is the duty cycle of the PWM input that is
assigned to the particular control bank. For the linear mapped
mode
current setting vs 8-bit brightness code.
the LED current is then a function of both the code in the pro-
grammed brightness register and the duty cycle input into the
assigned PWM inputs (PWM1 or PWM2).
ASSIGNING and ENABLING A PWM INPUT
To make the backlight current a function of the PWM input
duty cycle, one of the PWM inputs must first be assigned to
a particular Control Bank. This is done via bit [0] of the Control
A, B, or C PWM Registers (see
8). After assigning a PWM input to a Control Bank, the PWM
input is then enabled via bits [6:2] of the Control A/B/C PWM
Enable Registers. Each enable bit is associated with a spe-
cific Zone Target Register in I
ple, if Control A Zone Target 0 Register is configured as the
brightness register, then to enable PWM for that brightness
register, Control A PWM bit [2] would be set to 1.
ENABLING A CURRENT SINK
Once the brightness register and PWM inputs are configured
in I
cific control bank are enabled via the Control Enable Register
(see
tions for Control Bank A in I
would also apply to Control Bank B and Control Bank C.
2
C Current Control, the current sinks assigned to the spe-
Table
(Figure
14).
4) shows the typical response of % full-scale
Table 1
below shows the possible configura-
30115494
2
2
C Current Control. This table
C Current Control. For exam-
Table
6,
Table
www.national.com
7, or
Table