LM3509SDX National Semiconductor Corporation, LM3509SDX Datasheet - Page 16

• Manufacturer Part Number: LM3509SDX
• Description: High Efficiency Boost For White Led S And/or Oled Displays With Dual Current Sinks And I2c Compatible Brightness Control
• Manufacturer: National Semiconductor Corporation

www.national.com
TABLE 3. Operational Truth Table
* ENM ,ENS, or OLED high enables analog circuitry.
BRIGHTNESS REGISTERS (BMAIN and BSUB)
With the UNI bit (General Purpose register) set to 0 (Non-
Unison mode) both brightness registers (BMAIN and BSUB)
independently control the LED currents I
spectively. BMAIN and BSUB are both 8 bit, but with only the
5 LSB’s controlling the current. The three MSB’s are don’t
cares. The LED current control is designed to approximate an
exponentially increasing response of the LED current vs in-
creasing code in either BMAIN or BSUB (see Figure 9).
Program I
to GND, where:
UNI
X
X
X
1
1
0
0
0
LED_MAX
by connecting a resistor (RSET) from SET
OLED
0
0
0
0
0
0
1
1
ENM
0
1
0
0
1
1
1
0
FIGURE 7. Brightness MAIN Register Description
FIGURE 8. Brightness SUB Register Description
MAIN
and I
ENS
SUB/FB
X
X
X
X
0
1
0
1
re-
SUB/FB current sink disabled (SUB/FB configured as a feedback
SUB/FB current sink disabled (SUB/FB configured as a feedback
MAIN and SUB/FB current sinks enabled. Current levels set by
MAIN and SUB/FB current sinks enabled. Current levels set by
16
pin). MAIN current sink enabled current level set by BMAIN.
SUB/FB current sink enabled. Current level set by BSUB.
MAIN current sink enabled. Current level set by BMAIN.
. With the UNI bit (General Purpose register) set to 1 (Unison
mode), BSUB is disabled and BMAIN sets both I
FB
FB
cally 1%(with UNI = 0) to typically 0.15% (with UNI = 1). Figure
7 and Figure 8 show the register descriptions for the Bright-
ness MAIN and Brightness SUB registers. Table 4 and Figure
9 show I
age of I
. This prevents the independent control of I
, however matching between current sinks goes from typi-
contents of BMAIN and BSUB respectively.
LED_MAX
MAIN
pin). MAIN current sink disabled.
MAIN and SUB/FB Disabled
and/or I
.
contents of BMAIN.
LM3509 Disabled
SUB/FB
Result
vs. brightness data as a percent-
30004343
30004342
MAIN
MAIN
and I
and I
SUB/
SUB/