MAX16831 Maxim Integrated Products, MAX16831 Datasheet - Page 10

• Manufacturer Part Number: MAX16831
• Description: High-Power LED Driver
• Manufacturer: Maxim Integrated Products

The MAX16831 features a differential high-side level
shifter to drive an external n-channel MOSFET for dim-
ming. Wide contrast “pulsed” dimming (1000:1) is pos-
sible by applying either a low-frequency PWM input
signal or a DC voltage to the dimming input (DIM).
Protection features include peak current limiting,
HICCUP mode current limiting, output overvoltage pro-
tection, short-circuit protection, and thermal shutdown.
The HICCUP current-limit circuitry reduces the power
delivered to the load during severe fault conditions.
Nonlatching overvoltage protection limits the voltage on
the external switching MOSFET (Q
conditions in the LED string. During continuous opera-
tion at high input voltages, the power dissipation of the
MAX16831 could exceed the maximum rating and an
internal thermal shutdown circuitry safely turns off the
MAX16831 when the device junction temperature
exceeds +165°C. When the junction temperature drops
below the hysteresis temperature, the MAX16831 auto-
matically re-initiates startup.
The MAX16831 features a dual-purpose adjustable
UVLO input and enable function. Connect UVEN to V
through a resistive voltage-divider to set the undervolt-
age lockout (UVLO) threshold. The MAX16831 is
enabled when the UVEN exceeds the 1.244V (typ)
threshold. Drive UVEN to ground to disable the output.
The MAX16831 features a programmable UVLO thresh-
old. Connect UVEN directly to V
6.0V (max) UVLO threshold. Connect UVEN to V
through a resistive voltage-divider to select a UVLO
threshold (Figure 1). Calculate resistor values as follows:
where R
threshold voltage, and V
threshold in volts at V
The capacitor, C
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, then there can be jumps in the voltage at V
during dimming, which may cause the MAX16831 to
turn on and off when the dimming signal transitions
from low to high. The capacitor, C
High-Voltage, High-Power LED Driver with
Analog and PWM Dimming Control
10
______________________________________________________________________________________
UV1
R
+ R
UV
1
UV2
UVEN
Undervoltage Lockout/Enable
=
R
Setting the UVLO Threshold
≤ 270kΩ, V
UV
CC
, is required to prevent chattering
2
(Figure 1).
×
⎛
⎜
⎝
UVLO
V
UVLO
UVEN
V
CC
UVEN
is the desired UVLO
S
-
) under open-circuit
to select the default
V
UVEN
is the 1.244V (typ)
UVEN
⎞
⎟
⎠
, should be
CC
CC
CC
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.
The MAX16831 includes a factory-set 4ms (typ) 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
exceeds the UVLO threshold. Soft-start circuitry slowly
increases the internal soft-start voltage, V
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.
The MAX16831 includes a fixed 5V voltage regulator
REG1, a 7V voltage regulator REG2, and an internal 8V
regulator CLMP. REG1 and REG2 power up when V
exceeds the UVLO threshold. REG1 supplies power to
internal circuitry and remains on during PWM dimming.
It is capable of driving external loads up to 2mA.
REG2 is capable of delivering up to 20mA of current.
Connect REG2 to DRI to generate the supply voltage
for the primary switching MOSFET driver, DRV.
CLMP is powered by HI and supplies power to the cur-
rent-sense amplifier (CSA). CSA is enabled when
V
(V
also provides power to the dimming MOSFET control
circuitry. CLMP is the output of the CLMP 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 overshoots of the load current.
Figure 1. Setting the UVLO Threshold
CLMP
CLMP
C
UVEN
goes 2.5V above V
- V
V
IN
LO
) falls below 2.28V. The CLMP regulator
R
R
UV2
UV1
UVEN
LO
Internal Regulators
MAX16831
and is disabled when
QGND
V
CC
SS
Soft-Start
, resulting
CC
CC