IS31BL3230
Integrated Silicon Solution, Inc. – www.issi.com 8
Rev. B, 02/09/2015
APPLICATION INFORMATION
CIRCUIT DESCRIPTION
The IS31BL3230 is a white-LED driver with eight
matched current outputs. The matched current
regulators each has a 100:1 current ratio between the
LED
X
outputs and the I
SET
currents. The mirror controls
the current through the LEDs without the use of
external ballast resistors. With a total of 720mA of total
output current available, the IS31BL3230 is capable of
providing 90mA to each of the eight outputs through
the proper selection of the R
SET1
& R
SET2
resistor. LED
brightness control can be achieved on the IS31BL3230
with PWM signal.
SHUTDOWN
When the voltage on the active-high-logic PWM pin is
low, the IS31BL3230 will be in shutdown mode. While
disabled, the IS31BL3230 typically draws 1.6μA form
the power supply. There is no internal pull-up or
pull-down on the PWM pin of the IS31BL3230.
OUTPUT CURRENT CAPABILITY
The IS31BL3230 can provide up to 40mA of current to
each of the eight outputs given an input voltage of 2.7V
to 5.5V. An external resistor can be used to set the
output current, as approximated with the following the
equation:
R
SET1, 2
=100 × (V
ISET1, 2
/ I
LEDX
)
R
SET1
determines the constant current output of ports
LED1 thru LED4, R
SET2
determines the constant
current output of ports LED5 thru LED8, V
ISET
is the
voltage of R
SET
resistance, it is 1.20V typically. 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, using the
following equations to find the minimum input voltage
required:
V
CC
- V
LEDX
≥ V
HR
V
LEDX
is the diode forward voltage; V
HR
is typically as
shown in table1.
Table 1 I
LED
, R
SET
and V
HR-MIN
, V
CC
=3.6V
I
LED
R
SET
V
HEADROOM
10.0mA 12.0kΩ 27mV(typ.)
16.0mA 7.5kΩ 44mV(typ.)
20.0mA 6.0kΩ 53mV(typ.)
30.0mA 4.0kΩ 66mV(typ.)
40.0mA 3.0kΩ 75mV(typ.)
43.8mA 2.7kΩ 100mV(typ.)
62.5mA 2kΩ 150mV(typ.)
87.5mA 1.4kΩ 210mV(typ.)
PWM BRIGHTNESS CONTROL
Brightness control can be implemented by pulsing a
signal at the PWM pin.
The R
SET
value should be selected using the R
SET
equation. The LED brightness is proportional to the
duty cycle (D) of the PWM signal. The PWM frequency
(f) should be limited to accommodate the turn-on time
(t
ON
=50μs) of the device.
D × (1/f) > t
ON
f
MAX
= D
MIN
/ t
ON
If the PWM frequency is much less than 100Hz, flicker
may be seen in the LEDs. For the IS31BL3230, zero
duty cycle will turn off the LEDs and a 50% duty cycle
will result in an average I
LED
being half of the
programmed LED current. For example, if R
SET
is set
to program 16mA, a 50% duty cycle will result in an
average I
LED
of 8mA, I
LED
being half the programmed
LED current. R
SET
should be chosen not to exceed the
maximum current delivery capability of the device.
LED SELECTION
The IS31BL3230 has ultra low headroom voltage and
it is designed to drive white-LEDs with a typical forward
voltage up to 3.5V.
As the voltage drop below the recommend V
HR
, the
drive current will automatically scale down to reduce
the LED current consumption.
POWER DISSIPATION
The maximum allowable power dissipation that this
package can handle is determined by the following:
P
DMAX
= (T
JMAX
- T
A
)/θ
JA
Where T
JMAX
is the maximum junction temperature, T
A
is the ambient temperature and θ
JA
is the
junction-to-ambient thermal resistance of the specified
package. The IS31BL3230 come in the QFN-16
3mm×3mm package, and it has a junction-to-ambient
thermal resistance (θ
JA
) equal to 34.5°C/W. This value
of θ
JA
is highly dependant upon the layout of the PC
board. The actual power dissipated by the IS31BL3230
follows the equation:
P
DISS
= (V
CC
×I
CC
) - N(V
LEDX
× I
LEDX
)
Where N equals the number of active outputs, V
LEDX
is
the LED forward voltage, and I
LEDX
is the current
supplied to the LED.
INPUT CAPACITOR SELECTION
The IS31BL3230 is designed to run off of a fixed input
voltage. Depending on the stability and condition of
this voltage rail, it may be necessary to add some
small input capacitors to help filter out any noise that
may be present on the line. In the event that filtering is
