MAX16838ATP/V+ Maxim Integrated, MAX16838ATP/V+ Datasheet - Page 15

• Manufacturer Part Number: MAX16838ATP/V+
• Description: LED Lighting Drivers Integrated 2-Channel High-Brightness LED Drivers with High-Voltage DC-DC Controller
• Manufacturer: Maxim Integrated

Specifications of MAX16838ATP/V+

• Input Voltage: 4.75 V to 40 V
• Maximum Supply Current: 3.1 mA
• Power Dissipation: 2051 mW

Integrated, 2-Channel, High-Brightness LED Driver
EN is a logic input that completely shuts down the
device when connected to logic-low, reducing the
current consumption of the device to less than 15FA
(typ). The logic threshold at EN is 1.24V (typ). The volt-
age at EN must exceed 1.24V before any operation can
commence. There is a 71mV hysteresis on EN. The EN
input also allows programming the supply input UVLO
threshold using an external voltage-divider to sense the
input voltage, as shown in Figure 3. Use the following
equation to calculate the value of R1
Figure 3:
where V
V
R2
used.
The MAX16838 includes a current-foldback feature to
limit the input current at low V
divider between IN, CFB, and SGND to set the current-
foldback threshold. When the voltage at CFB goes below
1.23V, then the LED current starts reducing proportion-
ally to V
This feature can also be used for analog dimming of the
LEDs. Connect CFB to V
First, determine the required input supply voltage range,
the maximum voltage needed to drive the LED strings
including the minimum 1V across the constant LED
current sink (V
to drive the LED strings (I
Calculate the maximum duty cycle (D
following equation:
where V
V
V
frequency (f
ic response, and efficiency constraints.
ON
IN_MIN
LED
EN
is the desired input startup voltage. Choose an
D
between 10kI and 50kI. Connect EN to IN if not
is the output voltage. Select the switching
MAX
CFB
UVLOIN
D
with High-Voltage Boost and SEPIC Controller
is the minimum input supply voltage, and
is the forward drop of the rectifier diode,
.
SW
= (V
R1
LED
) depending on the space, noise, dynam-
EN
Applications Information
is the EN rising threshold (1.24V) and
LED
______________________________________________________________________________________
), and the total output current needed
=
+ V



V
UVLOIN
CC
D
V
LED
ON
– V
to disable this feature.
).
Boost-Circuit Design
IN_MIN
−
IN
1
. Connect a resistor-



×
)/(V
R2
Current Foldback
EN
EN
LED
MAX
Enable (EN)
and R2
) using the
+ V
D
)
EN
in
Figure
Threshold
Select the maximum peak-to-peak ripple on the inductor
current (IL
the maximum average inductor current (IL
peak inductor current (IL
Assuming IL
Calculate the minimum inductance value L
inductor current ripple set to the maximum value:
Choose an inductor that has a minimum inductance
greater than the calculated L
greater than IL
current limit of the selected inductor is 10% higher than
the inductor peak current. The IL
to have a higher ripple than 40%. Adjust the minimum
value of the inductance according to the chosen ripple.
One fact that must be noted is that the slope compensa-
tion is fixed and has a 120mV peak per switching cycle.
The dv/dt of the slope compensation ramp is 120f
Fs, where f
it is necessary to verify that the slope compensation is
adequate to prevent subharmonic oscillations. In the
case of the boost, the following criteria must be satisfied:
where L is the inductance value in FH, R
current-sense resistor value in ω, V
mum input voltage in V, V
f
If the inductance value is chosen to keep the inductor
in discontinuous conduction mode, the equation above
does not need to be satisfied.
SW
is the switching frequency in kHz.
3. Setting the MAX16838 Undervoltage Lockout
L
120f
P-P
MIN
SW
Inductor Selection in Boost Configuration
P-P
). Use the following equations to calculate
SW
is in kHz. After selecting the inductance
= V
IL
IL
MAX16838
is 40% of the average inductor current:
PEAK
PEAK
AVG
> R
IL
IN_MIN
P-P
CS
. The recommended saturation
= I
= IL
= IL
PEAK
(V
LED
x D
LED
AVG
LED
AVG
1.24V
/(1 - D
MAX
):
is the output voltage, and
- 2V
+ IL
MIN
x 0.4
/(f
EN
MAX
SW
IN_MIN
P-P
P-P
and current rating
IN_MIN
/2
x IL
)
can be chosen
V
IN
)/2L
P-P
MIN
R1
R2
is the mini-
EN
EN
AVG
)
CS
with the
) and
is the
SW
15
V/