MAX16834AGP/VY+T Maxim Integrated, MAX16834AGP/VY+T Datasheet - Page 10

• Manufacturer Part Number: MAX16834AGP/VY+T
• Description: LED Lighting Drivers High-Power LED Driver with Integrated High-Side LED Current Sense and PWM Dimming MOSFET Driver
• Manufacturer: Maxim Integrated

Specifications of MAX16834AGP/VY+T

• Input Voltage: 4.75 V to 28 V
• Maximum Supply Current: 10 mA
• Power Dissipation: 2051 mW

High-Power LED Driver with Integrated High-Side LED
Current Sense and PWM Dimming MOSFET Driver
The MAX16834 has a built-in transconductance amplifi-
er used to amplify the error signal inside the feedback
loop. The amplified current-sense signal is connected
to the negative input of the g
reference connected to REFI. The output of the op amp
is controlled by the input at PWMDIM. When the signal
at PWMDIM is high, the output of the op amp connects
to COMP; when the signal at PWMDIM is low, the out-
put of the op amp disconnects from COMP to preserve
the charge on the compensation capacitor. When the
voltage at PWMDIM goes high, the voltage on the com-
pensation capacitor forces the converter into a steady
state. COMP is connected to the negative input of the
PWM comparator with CMOS inputs, which draw very
little current from the compensation capacitor at COMP
and thus prevent discharge of the compensation
capacitor when the PWMDIM input is low.
The internal oscillator of the MAX16834 is programma-
ble from 100kHz to 1MHz using a single resistor at
RT/SYNC. Use the following formula to calculate the
switching frequency:
where RT is the resistor from RT/SYNC to SGND.
The MAX16834 synchronizes to an external clock signal
at RT/SYNC. The application of an external clock dis-
ables the internal oscillator allowing the MAX16834 to
use the external clock for switching operation. The
internal oscillator is enabled if the external clock is
absent for more than 50µs. The synchronizing pulse
minimum width for proper synchronization is 200ns.
CS is part of the current-mode control loop. The switch-
ing control uses the voltage on CS, set by R
nate the on pulse width of the switching cycle, thus
achieving peak current-mode control. Internal leading-
edge blanking is provided to prevent premature turn-off
of the switching MOSFET in each switching cycle.
The MAX16834 uses an internal-ramp generator for
slope compensation. The ramp signal also resets at the
beginning of each cycle and slews at the rate pro-
MAX16834
10
Internal Transconductance Error Amplifier
f
OSC
(kHz)
Slope Compensation (SC)
Current-Sense Input (CS)
=
5000k
RT(k )
m
amplifier with the current
Switching MOSFET
Ω
Internal Oscillator
Ω
×
(kHz)
CS
, to termi-
grammed by the external capacitor connected at SC.
The current source charging the capacitor is 100µA.
OVP+ sets the overvoltage threshold limit across the
LEDs. Use a resistive divider between output OVP+
and LV to set the overvoltage threshold limit. An internal
overvoltage protection comparator senses the differen-
tial voltage across OVP+ and LV. If the differential volt-
age is greater than 1.435V, NDRV is disabled and FLT
asserts. When the differential voltage drops by 200mV,
NDRV is enabled and FLT deasserts. The PWM dim-
ming MOSFET is still controlled by the PWMDIM input.
The MAX16834 features an active-low, open-drain fault
indicator (FLT). FLT asserts when one of the following
occurs:
1) Overvoltage across the LED string
2) Short-circuit condition across the LED string, or
3) Overtemperature condition
When the output voltage drops below the overvoltage
set point minus the hysteresis, FLT deasserts. Similarly
during the short-circuit period, the fault signal
deasserts when the dimming MOSFET is on, which
happens every hiccup cycle during short circuit. During
overtemperature fault, the FLT signal is the inverse of
the PWM input.
The UVLO threshold is set by resistors R1 and R2 (see
Figure 2). The MAX16834 turns on when the voltage
across R2 exceeds 1.435V, the UVLO threshold. Use
the following equation to set the desired UVLO thresh-
old:
In a typical application, use a 10kΩ resistor for R2 and
then calculate R1 based on the desired UVLO threshold.
The overvoltage threshold is set by resistors R4 and R9
(see Figure 2). The overvoltage circuit in the MAX16834
is activated when the voltage on OVP+ with respect to
LV exceeds 1.435V. Use the following equation to set
the desired overvoltage threshold:
Setting the Overvoltage Threshold
V
V
Applications Information
UVEN
Overvoltage Protection (OVP+)
OV
Setting the UVLO Threshold
=
=
1 435
.
1 435
.
V R
(
V R
Fault Indicator ( FLT )
(
4
1
+
+
R
R
9
2
)
)
R
R
9
2
Maxim Integrated