MAX16834_10 Datasheet, PDF (11/23 Pages) Maxim Integrated Products – High-Power LED Driver with Integrated High-Side LED Current Sense and PWM Dimming MOSFET Driver

High-Power LED Driver with Integrated High-Side LED
Current Sense and PWM Dimming MOSFET Driver
VIN
C1
R1
LV
FLT
L1
D1
LED+
C3
IN
NDRV
Q1
UVEN
LEDs
C2
HV
CS
SC ^MAX16834
ON
R4
R3
PWMDIM
OFF
LED-
RT/SYNC
C5
DIMOUT
Q2
R2
V_CC
C4
REF
SENSE+
OVP+
R6
R5
REFI
SGND
CLV
COMP
PGND
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 ∆I_L, and the peak inductor current IL_P in
amperes:
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