MAX16812ATI+ Maxim Integrated Products, MAX16812ATI+ Datasheet - Page 10

• Manufacturer Part Number: MAX16812ATI+
• Description: IC LED DRIVR HIGH BRIGHT 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: HBLED Driverr

Specifications of MAX16812ATI+

• Constant Current: Yes
• Topology: PWM, SEPIC, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive
• Type - Secondary: High Brightness LED (HBLED)
• Frequency: 125kHz ~ 500kHz
• Voltage - Supply: 5.5 V ~ 76 V
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Operating Temperature: -40°C ~ 125°C
• Internal Switch(s): Yes
• Number Of Segments: 2
• Low Level Output Current: 1.2 mA
• High Level Output Current: 1 A
• Operating Supply Voltage: 5.5 V to 76 V
• Maximum Supply Current: 2.5 mA
• Maximum Power Dissipation: 2759 mW
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Current - Output / Channel: -
• Efficiency: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Integrated High-Voltage LED Driver
with Analog and PWM Dimming Control
The MAX16812 features an adjustable UVLO through
the enable input (EN). Connect EN directly to IN to use
the 5V default UVLO. Connect EN to IN through a resis-
tive divider to ground to set the UVLO threshold. The
MAX16812 is enabled when V
(typ) threshold.
Calculate the EN UVLO resistor-divider values as fol-
lows (see Figure 2):
where R
EN threshold voltage, and V
voltage UVLO threshold in volts. Due to the 100mV hys-
teresis of the UVLO threshold, capacitor C
required to prevent chattering at the UVLO threshold
due to line impedance drops at power-up and during
dimming. If the undervoltage setting is very close to the
required minimum operating voltage, there can be
jumps in the voltage at IN while dimming. C
be large enough to limit the ripple on EN to less than
100mV (EN hysteresis) under these conditions so that it
does not turn on and off due to the ripple on IN.
The soft-start feature of the MAX16812 allows the LED
string current to ramp up in a controlled manner, thus
Figure 2. UVLO Threshold Setting
10
______________________________________________________________________________________
UV1
R
UV1
C
EN
is in the 20kΩ range, V
V
IN
=
R
UV2
R
R
UV2
UV1
x
⎛
⎜
⎝
V
Undervoltage Lockout
UVLO
EN
UVLO
V
MAX16812
EN
EN
- V
AGND
IN
is the desired input-
EN
exceeds the 1.38V
EN
is the 1.38V (typ)
⎞
⎟
⎠
Soft-Start
EN
should
EN
is
minimizing output-voltage overshoot. While the part is in
UVLO, C
of UVLO, an internal current source starts charging C
during the soft-start cycle. Use the following equation to
calculate total soft-start time:
where I
onds. Operation begins when REF ramps above 0.6V.
Once the soft-start is complete, REF is regulated to
1.238V, the internal voltage reference.
L_REG is the regulated (5.2V) internal supply voltage
capable of delivering 20mA. L_REG provides power to
the gate drive of the internal switching power MOSFET.
V
ceramic capacitor from L_REG to AGND.
H_REG is a low-dropout linear regulator referenced to
LV. H_REG provides the gate drive for the external
n-channel dimming MOSFET and also powers up the
MAX16812’s LED current-sense circuitry. Bypass
H_REG to LV with a 1µF ceramic capacitor.
Figure 3. Soft-Start Setting
L_REG
Switching MOSFET Driver Supply (L_REG)
REF
REF
is referenced to AGND. Connect a 3.3µF
C
REF
is 40µA, C
is discharged (Figure 3). Upon coming out
V
IN
t
ST
High-Side Regulator (H_REG)
=
REF
C
REF
is in µF, and t
REF
×
MAX16812
1 238
Low-Side Internal
I
REF
AGND
.
IN
ST
is in sec-
REF