LT3476 Просмотр технического описания (PDF) - Linear Technology
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LT3476 Datasheet PDF : 14 Pages
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LT3476
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
SHDN and PWM Pins Current vs
Voltage
SHDN and PWM Pins Threshold
vs Temperature
CAP Pins Overvoltage Threshold
vs Temperature
120
1.6
36.0
100
PWM 1-4
1.4
35.5
80
1.2
35.0
60
1.0
34.5
40
SHDN
0.8
34.0
20
0.6
33.5
0
0.4
33.0
0
4
8
12
16
–45 –20 5 30 55 80 105 130
–45 –20 5 30 55 80 105 130
PIN VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
3476 G10
3476 G11
3476 G12
Pin Functions
VC1, VC4, VC3, VC2, (Pins 1, 12, 13, 38): Error Ampli-
fier Compensation Pin. When PWM is low, VC pin floats
external compensation capacitor to save state for next cycle.
LED1, LED2, LED3, LED4, (Pins 2, 5, 8, 11): Non-
Inverting Input of Current Sense Error Amplifier. Connect
directly to LED current sense resistor terminal. Switcher
will regulate this node to a voltage of 0.1 • VADJ below the
CAP node. Also connected to CAP node through external
sense resistor and to anode of LED string. Do not allow
this pin to float independently of corresponding CAP input
pin. In applications where the LED current is low and the
PVIN changes widely, connect the output filter capacitor
to LEDn.
CAP1, CAP2, CAP3, CAP4, (Pins 3, 4, 9, 10): Inverting
input of current sense error amplifier. Connect directly to
other terminal of LED current sense resistor. Also con-
nected to output filter capacitor and cathode of external
Schottky rectifier. CAP greater than the overvoltage protect
threshold will inhibit switching.
RT (Pin 6): Oscillator Programming Pin. Place resistor
connected to GND to program oscillator frequency.
REF: (Pin 7): Reference Output Pin. Connect to VADJ pin
to get full-scale LED current. Connect to resistor dividers
to program VADJ pins to values lower than 1.05V. Bypass
to local GND with 0.1µF capacitor.
VADJ4, VADJ3, VADJ2, VADJ1, (Pins 14, 15, 36, 37): LED
Current Adjustment Pin. Sets voltage across external sense
resistor between CAPn and LEDn. Connect directly to
REF for full-scale threshold of 105mV, or use signal vales
between GND and REF to modulate LED current. VADJ pin
input range is 1.25V maximum.
PWM4, PWM3, PWM2, PWM1, (Pins 16, 17, 34, 35):
Signal low turns off the channel—disables the main switch,
reduces quiescent supply current to the channel, and causes
the VC pin for the channel to become high impedance.
SHDN (Pin 18): Shutdown Pin. Higher than 1.5V turns
the device on.
NC (Pins 19, 20, 21, 30, 31, 32): Not Used. Connect to
GND (Pin 39) for better heat dissipation.
SW4, SW3, SW2, SW1, (Pins 22, 23, 24, 25, 26, 27, 28, 29):
Switch Pin. Connect to external inductor and anode of external
Schottky rectifier. Minimize area of SW trace and use a
GND plane to reduce EMI. Adjacent pins of same name
are internally connected.
VIN (Pin 33): Input Supply Pin. Must be locally bypassed.
GND (Pin 39): Signal and Power GND. Solder exposed
pad directly to ground plane. The exposed pad metal of
the package provides both electrical contact to ground
and good thermal contact to the printed circuit board. It
must be soldered to the circuit board for proper operation.
3476fb
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