MAX16824 Datasheet, PDF (12/14 Pages) Maxim Integrated Products – High-Voltage, Three-Channel Linear High-Brightness LED Drivers

High-Voltage, Three-Channel Linear
High-Brightness LED Drivers
Another method of pulse dimming the outputs is to hold
LE high and drive OE with a PWM signal. Because the
input bits are always latched, the serial input constantly
refreshes the register. The control bits must be carefully
selected to dim the outputs properly.
A third method is to hold both LE and OE in the
enabled state. This allows the data bits to directly con-
trol the output channels, and hence, pulse dim the out-
put current. Make sure that the clock frequency does
not exceed the maximum rate at which the device can
change the state of the output channels.
Power Dissipation
The power dissipation (P_D) of the MAX16824/
MAX16825 is determined from the following equation:
P_D = (V_IN × I_IN) + (V_INL − V_LED1 − V_CS1) × (I_LED1 × DUTY1)
+ (V_INL − V_LED2 − V_CS2) × (I_LED2 × DUTY2)
+ (V_INL − V_LED3 − V_CS3) × (I_LED3 × DUTY3)
where:
V_IN = supply voltage
V_INL = supply Voltage to the LED strings
I_IN = supply current
V_{LED_} = total forward voltage for one LED string
I_{LED_} = LED current
V_CS = 200mV drop across R_{CS_}
DUTY = PWM_ duty cycle
The worst-case power dissipation occurs when the
drop across each internal MOSFET is at its maximum
with all three channels delivering the maximum allow-
able output current. The maximum drop across the
internal MOSFETs is determined by:
V_INL - V_{LED_} - V_{CS_} when V_{LED_} is at its minimum.
Higher ambient temperature increases the thermal stress
even further due to the reduction in voltage drop across
the LEDs. The MAX16824/MAX16825 thermal specifica-
tions are given according to the JEDEC-51 guidelines.
Good mechanical/thermal design practices must be
applied to help maintain the device junction temperature
below the absolute maximum ratings at all times.
Chip Information
PROCESS: BiCMOS-DMOS
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