MAX16834_15 Datasheet, PDF (11/23 Pages) Maxim Integrated Products – High-Power LED Driver with Integrated High-Side LED Current Sense and PWM Dimming MOSFET Driver

MAX16834
High-Power LED Driver with Integrated
High-Side LED Current Sense and
PWM Dimming MOSFET Driver
VIN
R1
R2
C1
LV
FLT
IN
NDRV
UVEN
HV
C2
CS
SC ^MAX16834
R3
PWMDIM
RT/SYNC
C5
V_CC
DIMOUT
C4
REF
SENSE+
OVP+
R6
R5
REFI
CLV
COMP
SGND
PGND
Q1
ON
OFF
L1
D1
R4
LED+
C3
LEDs
LED-
Q2
R8
R9
C7
C6
R7
R10
C8
Figure 2. Boost LED Driver
Programming the LED Current
The LED current is programmed using the voltage on
REFI and the LED current-sense resistor R10 (see
Figure 2). The current is given by:
I_LED
=
R10
V_REF × R5
× (R6 + R5) ×
9.9
(A)
where V_REF is 3.7V and the resistors R5, R6, and R10
are in ohms. The regulation voltage on the LED current-
sense resistor must not exceed 0.3V to prevent activa-
tion of the LED short-circuit protection circuit.
Boost Configuration
In the boost converter (Figure 2), the average inductor
current varies with the line voltage. The maximum aver-
age current occurs at the lowest line voltage. For the
boost converter, the average inductor current is equal
to the input current.
Calculate maximum duty cycle using the below equation.
D_MAX
=
V_LED + V_D − V_INMIN
V_LED + V_D − V_FET
where V_LED is the forward voltage of the LED string in
volts, V_D is the forward drop of the rectifier diode D1 in
volts (approximately 0.6V), V_INMIN is the minimum input
supply voltage in volts, and V_FET is the average drain to
source voltage of the MOSFET Q1 in volts when it is on.
Use an approximate value of 0.2V initially to calculate
D_MAX. A more accurate value of the maximum duty
cycle can be calculated once the power MOSFET is
selected based on the maximum inductor current.
Use the following equations to calculate the maximum
average inductor current IL_AVG, peak-to-peak inductor
current ripple ΔI_L, and the peak inductor current IL_P in
amperes:
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