Datasheet

ADM8845
Rev. C | Page 12 of 20
The main and sub display brightness of the ADM8845 can be
controlled together or separately by applying a digital PWM
signal to both CTRL1 and CTRL2 pins. The duty cycle of the
applied digital PWM signal determines the brightness of the
main and sub displays together. Varying the duty cycle of the
applied PWM signal also varies the brightness of the main and
sub displays from 0% to 100%.
By holding CTRL1 low and applying a digital PWM signal to
CTRL2, the sub display is turned off and the main display is
turned on. The brightness of the main display is then determined
by the duty cycle of the applied digital PWM signal.
By applying a digital PWM signal to CTRL1 and holding CTRL2
low, the sub display is turned on and the main display is turned
off. Then the brightness of the sub display is determined by the
duty cycle of the applied digital PWM signal.
By applying a digital PWM signal to CTRL1 and holding CTRL2
high, the sub display is turned on and the main display is turned
on. Then the brightness of the sub display is determined by the
duty cycle of the applied digital PWM signal. The brightness of
the main display is set to the maximum, which is set by R
SET
.
By holding CTRL1 high and applying a digital PWM signal to
CTRL2, the sub display is turned on and the main display is
turned on. Then the brightness of the main display is determined
by the duty cycle of the applied digital PWM signal. The bright-
ness of the sub display is set to the maximum, which is set by R
SET
.
When CTRL1 and CTRL2 go low, the LED current control
sinks shutdown. Shutdown of the charge pump is delayed by
15 ms. This timeout period (t
CP
) allows the ADM8845 to
determine if a digital PWM signal is present on CTRL1 and
CTRL2 or if the user has selected a full chip shutdown (see
Figure 25).
If digital PWM brightness control of the LEDs is not required, a
constant logic level 1 (V
CC
) or 0 (GND) must be applied.
The six white LEDs in the ADM8845 are arranged in two
groups, sub and main. It is possible to configure the six LEDs
as in Table 7. For more information, also refer to Figure 25.
Table 7. Digital Inputs Truth Table
CTRL1 CTRL2 LED Operation
0 0 Sub Display Off/Main Display Off (Full Shutdown)
1
0
, 2
1 Sub Display Off/Main Display On
1, 3
1 0 Sub Display On/Main Display Off
4, 2
1 1 Sub Display On/Main Display On (Full On)
4, 3
0 PWM Sub Display Off/Digital PWM Brightness Control on Main Display
1, 5
PWM 0 Digital PWM Brightness Control on Sub Display/Main Display Off
5, 2
1 PWM Sub Display On/ Digital PWM Brightness Control on Main Display
4, 5
PWM 1 Digital PWM Brightness Control on Sub Display/Main Display On
5
PWM PWM Digital PWM Brightness Control on Sub and Main Display
5
1
Sub Display Off means the sub display LEDs only is off. CTRL1 = 0 means a constant logic level (GND) is applied to CTRL1.
2
Main Display Off means the main display only is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2.
3
Main Display On means the display is on with the maximum brightness set by the R
SET
resistor. CTRL2 = 1 means a constant logic level (V
CC
) is applied to CTRL2.
4
Sub Display On means the display is on with the maximum brightness set by the R
SET
resistor. CTRL1 = 1 means a constant logic level (V
CC
) is applied to CTRL1.
5
PWM means a digital PWM signal is applied to the CTRL1 and/or the CTRL2 pin with a frequency from 100 Hz to 200 kHz.