LT3517
PIN FUNCTIONS
SW: Switch Pin. Minimize trace at this pin to reduce
EMI.
CTRL: LED Current Adjustment Pin. Sets voltage across
sense resistor between ISP and ISN. Connect directly to
V
forfull-scalethresholdof100mV,orusesignalvalues
REF
V : Input Supply Pin. Must be locally bypassed.
IN
betweenGNDand1VtomodulateLEDcurrent.TietheCTRL
pin to the V pin if not used.
SHDN: Shutdown Pin. Tie to 1.5V or higher to enable
device or 0.4V or less to disable device.
REF
V : g Error Amplifier Output Pin. Stabilize the loop with
C
m
V
: Reference Output Pin. This pin can supply up to
REF
100μA.
an RC network or compensating C.
FB: Voltage Loop Feedback Pin. Works as overvoltage
protection for LED drivers. If FB is higher than 1V, the
main switch is turned off.
R : Switching Frequency Adjustment Pin. Set switching
T
frequencyusingaresistortoGND(seeTypicalPerformance
Characteristics for values). For SYNC function, choose
the resistor to program a frequency 20% slower than the
SYNC pulse frequency. Do not leave this pin open.
TGEN: Top Gate Enable Input Pin. Tie to 1.5V or higher
to enable the PMOS driver function. Tie the TGEN pin to
ground if TG function is not used. There is an equivalent
40k resistor from TGEN pin to ground internally.
SYNC: Frequency Synchronization Pin. Tie an external
clock signal here. R resistor should be chosen to pro-
T
ISN: Current Sense (–) Pin. The inverting input to the
current sense amplifier.
gram a switching frequency 20% slower than SYNC pulse
frequency.Synchronization(powerswitchturn-on)occurs
a fixed delay after the rising edge of SYNC. Tie the SYNC
pin to ground if this feature is not used.
ISP: Current Sense (+) Pin. The noninverting input to the
current sense amplifier. Also serves as positive rail for
TG pin driver.
SS: Soft-Start Pin. Place a soft-start capacitor here. Leave
the pin open if not in use.
TG: Top Gate Driver Output. An inverted PWM sig-
nal drives series PMOS device between V
and
ISP
PWM: Pulse Width Modulated Input Pin. Signal low turns
(V – 7V). An internal 7V clamp protects the PMOS gate.
ISP
off channel, disables the main switch and makes the TG
Leave TG unconnected if not used.
pin high. Tie the PWM pin to V pin or SHDN pin if not
REF
used. There is an equivalent 50k resistor from PWM pin
Ground: Exposed Pad. Solder paddle directly to ground
plane.
to ground internally.
3517fa
6
Linear [ Linear ]
