MAX16816 Datasheet, PDF (16/33 Pages) Maxim Integrated Products – Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming

Programmable Switch-Mode LED Driver
with Analog-Controlled PWM Dimming
The capacitor C_UVEN is required to prevent chattering
at the UVLO threshold due to line impedance drops
during power-up and dimming. If the undervoltage set-
ting is very close to the required minimum operating
voltage, there can be large jumps in the voltage at V_CC
during dimming, which may cause the MAX16816 to
turn on and off when the dimming signal transitions
from low to high. The capacitor C_UVEN should be large
enough to limit the ripple on UVEN to less than the
100mV (min) UVEN hysteresis so that the device does
not turn off under these circumstances.
Soft-Start
The MAX16816 features a digitally programmable soft-
start delay that allows the load current to ramp up in a
controlled manner, minimizing output overshoot. Soft-
start begins once the device is enabled and V_CC
exceeds the UVLO threshold. Soft-start circuitry slowly
increases the internal soft-start voltage, V_SS, resulting
in a controlled rise of the load current. Signals applied
to DIM are ignored until the soft-start duration is com-
plete and a successive delay of 200µs has elapsed.
Use the Digital Soft-Start Duration register in the EEPROM
to select a soft-start duration from 0 (no delay) to
4.096ms. See the EEPROM and Programming section for
more information on using the Digital Soft-Start Duration
register.
Regulators (REG1, REG2, CLAMP)
The MAX16816 includes a fixed 5V voltage regulator,
REG1; an EEPROM-adjustable regulator, REG2; and an
internal 8V regulator, CLAMP. REG1 and REG2 power
up when V_CC exceeds the UVLO threshold. REG1 sup-
plies power to internal circuitry and remains on during
PWM dimming. REG1 is capable of driving external
loads up to 2mA.
Use the REG2 Control Register in the EEPROM to
select an output voltage from 5V to 15V for REG2.
Connect REG2 to DRI to generate the supply voltage
for the primary switching MOSFET driver, DRV. REG2 is
capable of delivering up to 20mA of current. See the
EEPROM and Programming section for more information
on configuring the REG2 output voltage.
CLAMP is powered by HI and supplies power to the
current-sense amplifier (CSA). CSA is enabled when
V_CLMP goes 2.5V above V_LO and is disabled when
(V_{CLMP -} V_LO) falls below 2.28V. The CLAMP regulator
also provides power to the dimming MOSFET control
circuitry. CLMP is the output of the CLAMP regulator.
Do not use CLMP to power external circuitry. Bypass
CLMP to LO with a 0.1µF ceramic capacitor. A larger
capacitor will result in overshoot of the load current.
Reference Voltage Output (REF)
The MAX16816 includes a 5% accurate, 3V (typ)
buffered reference output, REF. REF is a push-pull out-
put capable of sourcing/sinking up to 200µA of current
and can drive a maximum load capacitance of 100pF.
Connect REF to DIM through a resistive voltage-divider
to supply an analog signal for dimming. See the
Dimming Input (DIM) section for more information.
Dimming MOSFET Driver (DDR)
The MAX16816 requires an external n-channel MOSFET
for PWM dimming. Connect the MOSFET to the output of
the DDR dimming driver, DGT, for normal operation.
V_DGT swings between V_LO and V_CLMP. The DDR dim-
ming driver is capable of sinking or sourcing up to
20mA of current. The average current required to drive
the dimming MOSFET (I_{DRIVE_DIM}) depends on the
MOSFET’s total gate charge (Q_{G_DIM}) and the dimming
frequency of the converter, f_DIM. Use the following equa-
tion to calculate the supply current for the n-channel dim-
ming FET driver.
I_{DRIVE_DIM} = Q_{G_DIM} x f_DIM
n-Channel MOSFET Switch Driver (DRV)
The MAX16816 drives an external n-channel MOSFET
for switching. Use an external supply or connect REG2
to DRI to power the MOSFET driver. The driver output,
V_DRV, swings between ground and V_DRI. Ensure that
V_DRI remains below the absolute maximum V_GS rating
of the external MOSFET. DRV is capable of sinking 2A
or sourcing 1.4A of peak current, allowing the
MAX16816 to switch MOSFETs in high-power applica-
tions. The average current sourced to drive the external
MOSFET depends on the total gate charge (Q_G) and
operating frequency of the converter, f_SW. The power
dissipation in the MAX16816 is a function of the aver-
age output drive current (I_DRIVE). Use the following
equations to calculate the power dissipation in the
gate-driver section of the MAX16816 due to I_DRIVE:
I_DRIVE = Q_G x f_SW
P_D = I_DRIVE x V_DRI
where V_DRI is the supply voltage to the gate driver.
Dimming Input (DIM)
The dimming input, DIM, functions with either analog or
PWM control signals. Once the internal pulse detector
detects three successive edges of a PWM signal with a
frequency between 80Hz and 2kHz, the MAX16816
synchronizes to the external signal and pulse-width
modulates the LED current at the external DIM input
frequency with the same duty cycle as the DIM input. If
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