MAX16840_15 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – LED Driver with Integrated MOSFET

MAX16840
LED Driver with Integrated MOSFET
for MR16 and Other 12V AC Input Lamps
INPUT
COMP
CONTROL
RCF
VOLTAGE
CP
CZ
gm
2VP-P
L1
MAX16840
PWMC
DRIVER
5kI
10pF
LED+
SOURCE
FB
RCS
Figure 1. Control Loop
Peak-Limit Comparator
The IC has a peak-limit comparator that limits the peak
current in the switching MOSFET. If the current-sense
voltage on FB exceeds 0.65V, the peak-limit comparator
terminates switching for that switching cycle. This limits
the peak current in the switching MOSFET and the induc-
tor during transients.
PWM Comparator
The PWM comparator (PWMC) determines the on-time of
the switching MOSFET on a cycle-by-cycle basis by com-
paring the output of the gm amplifier to a 2VP-P ramp sig-
nal. At the start of each clock cycle, an RS flip-flop resets
and the gate driver turns on the switching MOSFET. The
comparator sets the flip-flop as soon as the ramp signal
exceeds the COMP voltage, thus terminating the on cycle.
Current-Reference Input (REFI)
The IC has a current-reference input (REFI). For VREFI >
1.2V, an internal reference sets the input average current
to 200mV/RCS. For VREFI < 1.2V, the input current is
reduced proportionally to VREFI, and it can be reduced
down to zero. The maximum withstand voltage of this
input is 6V. REFI has an internal current source of 50FA,
and the voltage on REFI can also be set with a resistor to
ground on REFI. This pin can also be used with an NTC
resistor on the pin to achieve thermal foldback.
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