cat4003b ON Semiconductor, cat4003b Datasheet - Page 7

• Manufacturer Part Number: cat4003b
• Description: Constant Current Programmable Led Driver With 32 Dimming Levels
• Manufacturer: ON Semiconductor

Pin Functions
VIN is the supply pin for the charge pump. A small 1 mF
ceramic bypass capacitor is required between the VIN pin
and ground near the device. The operating input voltage
range is from 2.4 V to 5.5 V. Whenever the input supply falls
below the under−voltage threshold (2.0 V), all the LED
channels are disabled and the device enters shutdown mode.
EN/DIM is the enable and one wire dimming input for all
LED channels. Levels of logic high and logic low are set at
1.3 V and 0.4 V respectively. When EN/DIM is initially
taken high, the CAT400XB becomes enabled and all LED
currents are set to the full scale 25 mA. To place the device
Basic Operation
accurately regulate LED current in each channel.
be programmed through the EN/DIM pin. 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.
to sink a constant regulated current of 20 mA. If the input
supply falls below 2.0 V, the under−voltage lockout circuit
disables all LED channels and resets the circuit to default
values. Any unused LED channels should be left open.
CAT400XB LED Current Selection
initially to the full scale currrent of 25 mA. The number of
pulses (n) on the EN/DIM input does decrease the current
value as follows:
The CAT400XB uses tightly matched current sinks to
There are 32 different settings for LED brightness that can
Each LED channel needs a minimum of 75 mV headroom
After power−up and once enabled, the LED current is set
LED current [mA] + 25
V
IN
EN/DIM
VIN
Figure 12. CAT4004B Functional Block Diagram
Reference
100 kΩ
31 * n
Voltage
31
Interface
Serial
Undervoltage
Lockout
http://onsemi.com
Setting DAC
Register
Current
7
into “zero current” shutdown mode, the EN/DIM pin must
be held low for 3 ms typical
LED1 to LED4 provide the internal regulated current for
each of the LED cathodes. There pins enter a high
impedance zero current state whenver the device is placed
in shutdown mode.
GND is the ground reference for the device. The pin must be
connected to the ground plane on the PCB.
TAB (CAT4004B only) is the exposed pad underneath the
package. For best thermal performance, the tab should be
soldered to the PCB and connected to the ground plane.
with n equal to zero.
enables and disables the device. The other function is LED
current dimming with 32 different levels by pulsing the input
signal, as shown on Figure 13. On each consecutive pulse
rising edge, the LED current is decreased by about 3.2%
(1/31th of the full scale value). After 30 pulses, the LED
current is 3.2% of the full scale current. On the 31
current drops to zero, and then goes back to full scale on the
following pulse.
Pulses faster than the minimum TLO may be ignored and
filtered by the device. Pulses longer than the maximum TLO
may shutdown the device. By pulsing the EN/DIM signal at
high frequency, the LED current can quickly be set to zero.
EN/DIM is held low for 3 ms typical.
EN/DIM after the power−up, as shown in Table 6.
The full scale current is calculated from the above formula
The EN/DIM pin has two primary functions. One function
Each pulse width should be between 200 ns and 100 ms.
The LED driver enters a “zero current” shutdown mode if
The dimming level is set by the number of pulses on the
4 Current Sink
Regulators
GND
st
pulse, the