IS31BL3212
Integrated Silicon Solution, Inc. – www.issi.com 6
Rev. C, 06/24/2014
APPLICATION INFORMATION
OUTPUT CURRENT CAPABILITY
In order for the output currents to be regulated properly,
sufficient headroom voltage (V
HR
) is required. The
headroom voltage refers to the minimum amount of
voltage that must be present across the current source
in order to ensure the desired current is realizable. To
ensure the desired current is obtained, apply the
following equations to find the minimum input voltage
required:
V
CC
- V
LEDX
≥ V
HR
Notice that if less than four LEDs connected, the left
pin can be floating or connected to GND.
FUNCTIONAL DESCRIPTION
The four constant current source outputs (D1 to D4)
can drive four individual LEDs with a maximum current
of 23mA each. The PCC wire serial interface enables
the IS31BL3212 and sets the current source
magnitudes.
CONSTANT CURRENT OUTPUT LEVEL SETTINGS
The constant current source levels for D1 to D4 are set
via the serial interface according to a logarithmic scale.
For the whole 16 codes, each code is approximately
1.5dB lower than the previous code. In this manner,
LED brightness appears linear with each increasing
code count. Because the outputs D1 to D4 are true
independent constant current sources, the voltage
observed on any single given output will be determined
by the actual forward voltage (V
F
) for the LED being
driven.
Since the output current sources of the IS31BL3212
are programmable, no PWM (pulse width modulation)
or additional control circuitry is needed to control LED
brightness. This feature greatly reduces the burden on
a microcontroller or system IC to manage LED or
display brightness, allowing the user to "set it and
forget it." With its high-speed serial interface (1MHz
data rate), the output current of the IS31BL3212 can
be changed successively to brighten or dim LEDs, in
smooth transitions (e.g., to fade-out) or in abrupt steps,
giving the user complete programmability and
real-time control of LED brightness.
PCC WIRE SERIAL INTERFACE
The current level magnitude is controlled by Pulse
Count Control (PCC wire) serial interface. The
interface records rising edges of the EN/SET pin and
decodes them into 16 different states. The 16 current
level settings available are indicated in Table 1.
Table 1: Current Level Setting
Data Output(mA/Ch) Data Output(mA/Ch)
1 23.0 9 5.8
2 19.6 10 4.8
3 16.1 11 4.1
4 13.8 12 3.5
5 11.8 13 2.8
6 9.9 14 2.1
7 8.1 15 1.4
8 6.9 16 0.7
The PCC wire serial interface has flexible timing.
After data is submitted, EN/SET is held high to latch
the data. Once EN/SET has been held in the logic high
state for time T
LAT
, the programmed current becomes
active and the internal data register is reset to zero.
For subsequent current level programming, the
number of rising edges corresponding to the desired
code must be entered on the EN/SET pin.
PCC WIRE SERIAL INTERFACE TIMING
When EN/SET is held low for an amount of time
greater than T
OFF
, the IS31BL3212 enters into
shutdown mode and draws 1.0µA typically from V
CC
.
The internal data register is reset to zero during
shutdown.
