LM36922H Datasheet, PDF (12/46 Pages) Texas Instruments – Highly Efficient Dual-String White LED Driver

LM36922H
SNVSAF2A – FEBRUARY 2016 – REVISED FEBRUARY 2016
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Feature Description (continued)
7.3.2 LM36922H Start-Up
The LM36922H can be enabled or disabled in various ways. When disabled, the device is considered shutdown,
and the quiescent current drops to I_SHDN. When the device is in standby, it returns to the I_SHDN current level
retaining all programmed register values. Table 1 describes the different operating states for the LM36922H.
Table 1. LM36922H Operating Modes
LED STRING
ENABLES
0x10 bits[2:1]
XXX
0
At least one
enabled
At least one
enabled
At least one
enabled
At least one
enabled
At least one
enabled
At least one
enabled
At least one
enabled
PWM INPUT
X
X
X
I²C BRIGHTNESS
REGISTERS
0x18 bits[2:0]
0x19 bits[7:0]
XXX
XXX
0
BRIGHTNESS
MODE
0x11 bits[6:5]
XX
XX
00
DEVICE
ENABLE
0x10 bit[0]
0
1
1
X
Code > 000
00
1
0
PWM Signal
XXX
XXX
01
1
01
1
0
XXX
10 or 11
1
X
0
10 or 11
1
PWM Signal
Code > 000
10 or 11
1
LED CURRENT
(EXP MAPPING)
0x11 bit[7] = 1
(LIN MAPPING)
0x11 bit[7] = 0
Off, device disabled
Off, device standby
Off, device in standby
I_LED = 50 µA ×
1.003040572^Code
See ⁽¹⁾
Off, device in standby
LED = 37.806 µA + 12.195
µA × Code
See ⁽¹⁾
I_LED = 50 µA ×
1.003040572^CodeSee ⁽¹⁾
LED = 37.806 µA + 12.195
µA × Code
See ⁽¹⁾
Off, device in standby
Off, device in standby
I_LED = 50 µA ×
1.003040572^CodeSee ⁽¹⁾
LED = 37.806 µA + 12.195
µA × Code
See ⁽¹⁾
(1) Code is the 11-bit code output from the ramper (see Figure 21, Figure 23, Figure 25, Figure 27). This can be the I²C brightness code,
the converted PWM duty cycle or the 11-bit product of both.
7.3.3 Brightness Mapping
There are two different ways to map the brightness code (or PWM duty cycle) to the LED current: linear and
exponential mapping.
7.3.3.1 Linear Mapping
For linear mapped mode the LED current increases proportionally to the 11-bit brightness code and follows the
relationship:
+_.'& = 37.806ä# +12.195ä# × %K@A
(1)
This is valid from codes 1 to 2047. Code 0 programs 0 current. Code is an 11-bit code that can be the I²C
brightness code, the digitized PWM duty cycle, or the product of the two.
7.3.3.2 Exponential Mapping
In exponential mapped mode the LED current follows the relationship:
+_.'& = 50J# × 1.003040572^%K@A
(2)
This results in an LED current step size of approximately 0.304% per code. This is valid for codes from 1 to
2047. Code 0 programs 0 current. Code is an 11-bit code that can be the I²C brightness code, the digitized PWM
duty cycle, or the product of the two. Figure 17 details the LED current exponential response.
The 11-bit (0.304%) per code step is small enough such that the transition from one code to the next in terms of
LED brightness is not distinguishable to the eye. This therefore gives a perfectly smooth brightness increase
between adjacent codes.
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