LT3799
PIN FUNCTIONS
V
IN
(Pin 11):
Input Voltage. This pin supplies current to
the internal start-up circuitry and to the INTV
CC
LDO. This
pin must be locally bypassed with a capacitor. A 25V shunt
regulator is internally connected to this pin.
INTV
CC
(Pin 13):
Regulated Supply for Internal Loads
and GATE Driver. Supplied from V
IN
and regulates to 10V
(typical). INTV
CC
must be bypassed with a 4.7µF capacitor
placed close to the pin.
COMP
+
,
(Pin 7, Pin 8):
Compensation Pins for
Internal Error Amplifier. Connect a capacitor between these
two pins to compensate the internal feedback loop.
DCM (Pin 10):
Discontinuous Conduction Mode Detection
Pin. Connect a capacitor and resistor in series with this
pin to the third winding.
V
IN_SENSE
(Pin 16):
Line Voltage Sense Pin. The pin is used
for sensing the AC line voltage to perform power factor
correction. Connect the output of a resistor divider from
the line voltage to this pin. The voltage on this pin should
be between 1.25V to 1.5V at the maximum input voltage.
CTRL1, CTRL2, CTRL3 (Pin 1, Pin 2, Pin 3):
Current Output
Adjustment Pins. These pins control the output current.
The lowest value of the three CTRL inputs is compared to
the negative input of the operational amplifier. Due to the
unique nature of the LT3799 control loop, the maximum
current does not directly correspond to the V
CTRL
voltages.
SENSE (Pin 15):
The Current Sense Input for the Control
Loop. Kelvin connect this pin to the positive terminal of
the switch current sense resistor, R
SENSE
, and the source
of the N-channel MOSFET. The negative terminal of the
current sense resistor should be connected to the GND
plane close to the IC.
COMP
–
GATE (Pin 14):
N-Channel MOSFET Gate Driver Output.
Switches between INTV
CC
and GND. This pin is pulled to
GND during shutdown state.
FB (Pin 9):
Voltage Loop Feedback Pin. FB is used to
detect open LED conditions by sampling the third winding
voltage. An open LED condition is reported if the CT pin
is high and the FB pin is higher than 1.25V.
CT (Pin 6):
Timer Fault Pin. A capacitor is connected
between this pin and ground to provide an internal timer
for fault operations. During start-up, this pin is pulled to
ground and then charged with a 10µA current. Faults related
to the FB pin will be ignored until the CT pin reaches 1.25V.
If a fault is detected, the controller will stop switching and
begin to discharge the CT capacitor with a 200nA pull-down
current. When the pin reaches 240mV, the controller will
start to switch again.
FAULT
(Pin 5):
Fault Pin. An open-collector pull-down on
FAULT
asserts if FB is greater than 1.25V with the CT pin
higher than 1.25V.
V
REF
(Pin 4):
Voltage Reference Output Pin, Typically 2V.
This pin drives a resistor divider for the CTRL pin, either
for analog dimming or for temperature limit/compensation
of LED load. Can supply up to 200µA.
GND (Exposed Pad Pin 17):
Ground. The exposed pad
of the package provides both electrical contact to ground
and good thermal contact to the printed circuit board.
The exposed pad must be soldered to the circuit board
for proper operation.
3799p
7
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