CAT4016, CAV4016
www.onsemi.com
9
Block Diagram
Figure 17. CAT4016 Functional Block Diagram
Current
Setting
+
CURRENT
SINKS
LATCHES
SHIFT
REGISTER
1.2 V Ref
GND
+
RSET
BLANK
VIN
VDD
LED1 LED2 LED3 LED16
CLK
SIN
LATCH
L1 L2 L3
L16
S1 S2 S3
S16
SOUT
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 0.4 V 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 17 ns (typical). Relative to LED1, LED2
is delayed by 17 ns, LED3 by 34 ns and LED16 by 250 ns
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 than 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).
