Datasheet

Evaluates: MAX16834
LED Dimming Operation
Jumper JU1 configures the MAX16834 EV kit for analog
linear dimming or PWM dimming control of the external
LEDs. Install a shunt across jumper JU1 to control the
LED brightness using a linear voltage applied at the
MAX16834 REFI pin. Remove the shunt at jumper JU1 to
control the LED brightness using a PWM signal applied
at the PWMDIM and SGND PCB pads. See Table 1 for
jumper JU1 settings for LED dimming operation.
Linear Dimming Control
The MAX16834 EV kit offers analog linear dimming of
the external LEDs connected between the LED+ and
LED- PCB pads. Resistor R5 and potentiometer R17 set
the external LEDs’ maximum average current to 1A by
adjusting the voltage at the MAX16834 REFI input. Vary
the MAX16834’s REFI voltage using potentiometer R17
to adjust the LEDs’ brightness. LED brightness increas-
es when the voltage at REFI is increased and vice
versa. The MAX16834 REFI pin voltage can be moni-
tored by placing a voltmeter across the REFI and
SGND PCB pads. The LED string dimming current can
be adjusted using the following equation:
V
REFI
= 9.9 × I
LED
× R5
where V
REFI
is the voltage at the REFI PCB pad, I
LED
is
the LED current in amperes, and R5 is the sense resistor,
in ohms, connected between N1’s source and the
MAX16834 LV pin.
Digital PWM Dimming Operation
LED dimming can be achieved on the MAX16834 EV kit
by applying a digital PWM signal at the EV kit’s
PWMDIM and SGND PCB pads. Connect a PWM signal
with a 1.5V to 5V logic-high level and frequencies from
DC to 20kHz. Vary the PWM signal duty cycle to adjust
the LEDs’ brightness.
Fault Indicator ( FLT )
The MAX16834EV kit features an output pad (FLT) to
monitor the FLT output logic signal. FLT is low when
any of the following conditions occur:
• Open-circuit condition across the LED+ and LED-
PCB pads
• Short-circuit condition across the LED+ and LED-
PCB pads
• MAX16834 IC overtemperature fault condition
When the LED+ voltage drops below the programmed
overvoltage set point minus the MAX16834 hysteresis,
FLT deasserts. During a short-circuit condition, FLT
deasserts when dimming MOSFET N1 is on. The FLT
signal is the inverse of the PWMDIM signal during an
overtemperature fault condition (T
J
> 140°C).
Output Overvoltage Protection
The maximum voltage on the LED+ pin is limited to
34.7V with respect to LV by a feedback network
formed by resistors R11 and R12. When the LED+ to
LV voltage difference exceeds the programmed 34.7V
threshold, PWM switching is terminated, FLT asserts
low, and no further energy is transferred to the load
connected between the LED+ and LED- PCB pads.
Refer to the Setting the Overvoltage Threshold section
in the MAX16834 IC data sheet for setting the overvolt-
age threshold.
Optional Automotive Load Dump
Protection (Boost Mode Only)
The MAX16834 EV kit provides PCB component foot-
prints for an optional load dump protection circuit (C19,
D5, Q1, and R21). This limits the MAX16834 IN pin volt-
age below its absolute maximum 30V rating when oper-
ating the EV kit circuit in boost-mode operation under
load dump conditions.
When configuring the MAX16834 EV kit for load dump
operation, remove resistor R3. NPN transistor Q1
should have a 75V/100mA (min) rating. Zener diode D5
should have a 24V/100mA rating.
Reconfiguring the MAX16834 EV Kit
for Buck-Boost Operation
The MAX16834 EV kit can be reconfigured for buck-
boost operation by removing and adding the following
components:
• Remove resistors R4 and R8.
• Install a 0Ω resistor at R3.
• Install components at D1 (6V zener) and R7 (2.7kΩ).
MAX16834 Evaluation Kit
4 _______________________________________________________________________________________
Table 1. JU1 Jumper Selection
SHUNT
POSITION
PWMDIM PIN
EV KIT DIMMING
OPERATION
Installed
Connects to
R14/R20 network
Linear dimming control
Not
installed
Connects to external
PWM signal
PWM dimming control