MAX16816 Datasheet, PDF (22/33 Pages) Maxim Integrated Products – Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming

Programmable Switch-Mode LED Driver
with Analog-Controlled PWM Dimming
Fault Protection
The MAX16816 features built-in overvoltage protection,
overcurrent protection, HICCUP mode current-limit pro-
tection, and thermal shutdown. Overvoltage protection
is achieved by connecting OV to HI through a resistive
voltage-divider. HICCUP mode limits the power dissi-
pation in the external MOSFETs during severe fault
conditions. Internal thermal shutdown protection safely
turns off the converter when the IC junction temperature
exceeds +165°C.
Overvoltage Protection
The overvoltage protection (OVP) comparator com-
pares the voltage at OV with a 1.235V (typ) internal ref-
erence. When the voltage at OV exceeds the internal
reference, the OVP comparator terminates PWM
switching and no further energy is transferred to the
load. The MAX16816 reinitiates soft-start once the over-
voltage condition is removed. Connect OV to HI
through a resistive voltage-divider to set the overvolt-
age threshold at the output.
Setting the Overvoltage Threshold
Connect OV to HI or to the high-side of the LEDs
through a resistive voltage-divider to set the overvolt-
age threshold at the output (Figure 4). The overvoltage
protection (OVP) comparator compares the voltage at
OV with a 1.235V (typ) internal reference. Use the fol-
lowing equation to calculate resistor values:
R _OV1
=
R _OV2
x
⎛
⎝⎜
V_{OV_LIM} −
V_OV
V_OV
⎞
⎠⎟
where V_OV is the 1.235V OV threshold. Choose R_OV1
and R_OV2 to be reasonably high value resistors to pre-
vent discharge of filter capacitors. This will prevent
unnecessary undervoltage and overvoltage conditions
during dimming.
Load-Dump Protection
The MAX16816 features load-dump protection up to 76V.
LED drivers using the MAX16816 can sustain single fault
load dump events. Repeated load dump events within
very short time intervals can cause damage to the dim-
ming MOSFET due to excess power dissipation.
Thermal Shutdown
The MAX16816 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds +165°C. Outputs are enabled again when the
die temperature drops below +145°C.
Applications Information
Inductor Selection
The minimum required inductance is a function of oper-
ating frequency, input-to-output voltage differential, and
the peak-to-peak inductor current (ΔI_L). Higher ΔI_L
allows for a lower inductor value while a lower ΔI_L
requires a higher inductor value. A lower inductor value
minimizes size and cost, improves large-signal tran-
sient response, but reduces efficiency due to higher
peak currents and higher peak-to-peak output ripple
voltage for the same output capacitor. On the other
hand, higher inductance increases efficiency by reduc-
ing the ripple current, ΔI_L. However, resistive losses
due to extra turns can exceed the benefit gained from
lower ripple current levels, especially when the induc-
tance is increased without also allowing for larger
inductor dimensions. A good compromise is to choose
ΔI_L equal to 30% of the full load current. The inductor
saturating current is also important to avoid runaway
current during the output overload and continuous
short circuit. Select the I_SAT to be higher than the maxi-
mum peak current limit.
Buck configuration: In a buck configuration the average
inductor current does not vary with the input. The worst-
case peak current occurs at high input voltage. In this
case the inductance, L, for continuous conduction
mode is given by:
( ) L = VOUT x VINMAX − VOUT
V_INMAX x f_SW x ΔI_L
where V_INMAX is the maximum input voltage, f_SW is the
switching frequency, and V_OUT is the output voltage.
V_LED+
R_OV1
R_OV2
MAX16816
OV
AGND
Figure 4. Setting the Overvoltage Threshold
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