Rainbow Electronics MAX16834 User Manual

Page 9

MAX16834

Undervoltage Lockout/Enable

The MAX16834 features an adjustable UVLO using the
enable input (UVEN). Connect UVEN to V

through a

resistive divider to set the UVLO threshold. The
MAX16834 is enabled when the V

UVEN

exceeds the

1.435V (typ) threshold. See the

Setting the UVLO

Threshold

section for more information.

UVEN also functions as an enable/disable input to the
device. Drive UVEN low to disable the output and high
to enable the output.

Reference Voltage (REF)

The MAX16834 features a 3.7V reference output, REF.
REF provides power to most of the internal circuit blocks
except for the output drivers and is capable of sourcing
1mA to external circuits. Connect a 0.1µF to 0.22µF
ceramic capacitor from REF to SGND. Connect REF to
REFI through a resistive divider to set the LED current.

Reference Input (REFI)

The output current is proportional to the voltage at
REFI. Applying an external DC voltage at REFI or using
a potentiometer from REF to SGND allows analog dim-
ming of the output current.

High-Side Reference Voltage Input (LV)

LV is a reference input. Connect LV to SGND for boost
and SEPIC topologies. Connect LV to IN for buck-boost
and high-side buck topologies.

Dimming Driver Regulator

Input Voltage (HV)

The voltage at HV provides the input voltage for the
dimming driver regulator. For boost or SEPIC topology,
connect HV either to IN or to V

. For buck-boost, con-

nect HV to a voltage higher than IN. The voltage at HV
must not exceed 28V with respect to PGND. For the
high-side buck, connect HV to IN.

Dimming MOSFET Driver (DIMOUT)

The MAX16834 requires an external n-channel MOSFET
for PWM dimming. Connect the gate of the MOSFET to
the output of the dimming driver, DIMOUT, for normal
operation. The dimming driver is capable of sinking or
sourcing up to 50mA of current.

n-Channel MOSFET Switch Driver (NDRV)

The MAX16834 drives an external n-channel switching
MOSFET. NDRV swings between V

and PGND.

NDRV is capable of sinking/sourcing 3A of peak current,
allowing the MAX16834 to switch MOSFETs in high-
power applications. The average current demanded
from the supply to drive the external MOSFET depends
on the total gate charge (Q

) and the operating

frequency of the converter, f

. Use the following equa-

tion to calculate the driver supply current I

NDRV

required for the switching MOSFET:

NDRV

= Q

x f

Pulse Dimming Inputs (PWMDIM)

The MAX16834 offers a dimming input (PWMDIM) for
pulse-width modulating the output current. PWM dim-
ming can be achieved by driving PWMDIM with a pul-
sating voltage source. When the voltage at PWMDIM is
greater than 1.435V, the PWM dimming MOSFET turns
on and when the voltage on PWMDIM is below 1.235V,
the PWM dimming MOSFET turns off.

High-Side Linear Regulator (V

CLV

)

The MAX16834’s 5V high-side regulator (CLV) powers
up the dimming MOSFET driver. V

CLV

is measured with

respect to LV and sources up to 2mA of current.
Bypass CLV to LV with a 0.1µF to 1µF low-ESR ceramic
capacitor. The maximum voltage on CLV with respect
to PGND must not exceed 28V. This limits the input volt-
age for buck-boost topology.

Low-Side Linear Regulator (V

)

The MAX16834’s 7V low-side linear regulator (V

) pow-

ers up the switching MOSFET driver with sourcing capa-
bility of up to 50mA. Use at least a 1µF low-ESR ceramic
capacitor from V

to PGND for stable operation.

LED Current-Sense Input (SENSE+)

The differential voltage from SENSE+ to LV is fed to an
internal current-sense amplifier. This amplified signal is
then connected to the negative input of the transcon-
ductance error amplifier. The voltage gain factor of this
amplifier is 9.9 (typ).

Internal Transconductance Error Amplifier

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

amplifier with the current

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.

High-Power LED Driver with Integrated High-Side LED

Current Sense and PWM Dimming MOSFET Driver

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