CAT4026_11 Datasheet, PDF (9/14 Pages) ON Semiconductor – 6-Channel LED Controller

CAT4026
Pin Functions
VDD
The VDD input is the positive supply to the devices. VDD
should be nominally 5 V.
PWM
The PWM control input provides multiple functions.
When the first rising edge is applied to PWM input, the
CAT4026 will immediately power−up and remain powered
up until the PWM input has been held low for at least
typically 25 ms, at which point the device will enter full
shutdown mode and draw zero current.
When PWM is active (high level), all LED channels are
enabled. When PWM is inactive (low level), all LED
channels are disabled. For PWM dimming frequencies in the
300 Hz range, duty cycles as low as 0.1% are supported.
An internal pull−down resistor (120 kW typical) exists on
the PWM input. PWM logic high and low detection levels
are typically set at 1.2 V and 1.0 V respectively.
ANLG
The ANLG controlled input allows the full scale
brightness level of all channels to be globally reduced. When
the ANLG control is taken below 3 V, the maximum LED
brightness will be equal to 1/3 of the ANLG pin voltage. If
the ANLG pin is taken above 3 V, it will have no further
effect and the brightness will remain at the full scale (100%)
setting.
An internal resistive network to ground (150 kW typical)
exists on the ANLG pin. The external source resistance
driving this input should be taken into consideration when
controlling the ANLG input.
A simple power derating external circuit can be applied to
the ANLG pin whenever excessive voltage is present on any
LED cathode.
If the ANLG control function is not required, the pin
should be pulled high (above 3 V) to ensure full scale
brightness is maintained.
BASE[1:6]
The BASE output pin drives the base of the external NPNs
to regulate the LED current in the associated string to the
preset value. External high−voltage bipolar junction
transistors, such as MJD340, are recommended.
Operating base currents up to 5 mA can be powered from
each of the BASE pins in normal operating conditions. In the
event of any BASE pin being shorted directly to GND,
internal protection circuitry will limit the drive current to
15 mA (typically).
RSET[1:6]
The RSET input pins sense the voltage of the external
LED current bias resistors. Each RSET pin is accurately
regulated to a voltage of 1.0 V under the full scale brightness
condition (ANLG > 3.0 V).
Each RSET pin contains internal compensating circuitry
to eliminate the operating base current, thereby maintaining
extremely accurate LED matching on all channels.
FLT−OCA
The FLT−OCA flag output is active low (open−drain) and
is latched whenever an Open Cathode−Anode fault
condition has been detected on any LED string. An external
pull−up resistor (10 kW) should be connected to FLT−OCA.
For systems requiring complete shutdown upon detection
of any open−LED channel, the FLT−OCA output can be
used to drive the shutdown control of the LED power supply.
For systems which must continue operation under
open−LED channels, the FLT−OCA should only be used for
diagnostic purposes (not for system shutdown).
The FLT−OCA is cleared upon power−down of the
CAT4026 device.
FLT−SCA
The FLT−SCA flag output is active low (open−drain) and
becomes active whenever any LED cathode terminal
exceeds a user programmed voltage level (at the SCA pin,
set by an external zener diode). An external pull−up resistor
(10 kW) should be connected to the FLT−SCA pin.
For systems requiring complete shutdown upon detection
of any faulty LED channel, the FLT−SCA output can be used
to drive the shutdown control of the LED power supply.
For systems which must continue operation under faulty
LED channels, the FLT−SCA should only be used for
diagnostic purposes (not for system shutdown). In this case,
the FLT−SCA flag can be used to trigger an external power
derating circuit reducing the applied voltage at the ANLG
control input, thereby reducing the power dissipated in the
external bipolar channel transistors.
Note: If an Open−LED channel is present, the FLT−SCA
flag may become temporary active (depending on the user
threshold levels) while the system is diagnosing the
Open−channel fault. When the system has eventually
cleared (disabled) the open−channel, the fault FLT−SCA
will automatically clear itself once the system has stabilized
and returned back to normal operating conditions.
IFB
The IFB pin is a pull−down current sink with a drive level
determined by the lowest LED cathode voltage as shown
below.
VCS Voltage
> 4.1 V
3.3 V
< 3.1 V
VCS = Vcathode + Vdiode
IFB Drive Current (typ)
0 mA
0.5 mA
1.0 mA
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