CAT4016 Datasheet, PDF (9/15 Pages) Catalyst Semiconductor – 16-Channel Constant Current LED Driver

BLOCK DIAGRAM
VDD
VIN
BLANK
LATCH
CAT4016
LED1 LED2 LED3
LED16
CURRENT
SINKS
L1 L2 L3
LATCHES
L16
+
Current
Setting
1.2V Ref
RSET
GND
SHIFT
REGISTER
SIN
S1 S2 S3
S16
SOUT
CLK
Figure 2. CAT4016 Functional Block Diagram
BASIC OPERATION
The CAT4016 uses 16 tightly matched current sinks to
accurately regulate the LED current in each channel.
The external resistor, R_SET, is used to set the LED
channel current to 50 times the current in R_SET.
LED current = 50 × ^1.2
R _SET
Tight current regulation for all channels is possible
over a wide range of input and LED voltages due to
independent current sensing circuitry on each
channel. The LED channels have a maximum dropout
of 0.4V for most current and supply voltage
conditions. This helps improve the heat dissipation
and efficiency of the LED driver.
Upon power-up, an under-voltage lockout circuit
clears all latches and shift registers and sets all
outputs to off. Once the under-voltage lockout
threshold has been reached the device can be
programmed.
The driver delays the activation of each consecutive
LED output channel by 17ns (typical). Relative to
LED1, LED2 is delayed by 17ns, LED3 by 34ns and
LED16 by 250ns typical. The delay is introduced when
LATCH is activated. The delay minimizes the inrush
current on the LED supply by staggering the turn on
and off current spikes over a period of time and
therefore allowing usage of smaller bypass capacitors.
Pull-up and pull-down resistors are internally provided
to set the state of the BLANK and LATCH pins to the
off-state when not externally driven.
SERIAL INTERFACE
A high-speed serial 4-wire interface is provided to
program the state of each LED on or off. The
interface contains a 16-bit serial to parallel shift
register (S1-S16) and a 16-bit latch (L1-L16).
Programming the serial to parallel register is
accomplished via SIN and CLK input pins. On each
rising edge of the CLK signal, the data from SIN is
moved through the shift register serially. Data is also
moved out of SOUT which can be connected to a next
device if programming more then one device on the
same interface.
On the rising edge of LATCH, the data contents of the
serial to parallel shift register is reflected in the
latches. On the falling edge of LATCH, the state of the
serial to parallel register at that particular time is
saved in the latches and does not change irrespective
of the contents of the serial to parallel register.
BLANK is used to disable all LEDs (turn off)
simultaneously while maintaining the same data in the
latch register. When low, the LED outputs reflect the
data in the latches. When high, all outputs are high
impedance (zero current).
© Catalyst Semiconductor, Inc.
9
Characteristics subject to change without notice
Doc. No. MD-5028 Rev. B