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PDF LT8391 Data sheet ( Hoja de datos )
| Número de pieza | LT8391 | |
| Descripción | 60V Synchronous 4-Switch Buck-Boost LED Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT8391 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
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FEATURES
nn 4-Switch Single Inductor Architecture Allows VIN
Above, Below or Equal to VOUT
nn Synchronous Switching: Up to 98% Efficiency
nn Proprietary Peak-Buck Peak-Boost Current Mode
nn Wide VIN Range: 4V to 60V
nn Wide VOUT Range: 0V to 60V (51V LED)
nn ±3% LED Current Accuracy
nn 2000:1 External and 128:1 Internal PWM Dimming
nn High Side PMOS PWM Switch Driver
nn Integrated Bootstrap Diodes
nn No Top MOSFET Refresh Noise in Buck or Boost
nn Adjustable and Synchronizable: 150kHz to 650kHz
nn Flicker-Free Spread Spectrum for Low EMI
nn Open and Short LED Protection with Fault Reporting
nn Available in 28-Lead TSSOP with Exposed Pad and
28-Lead QFN (4mm × 5mm)
APPLICATIONS
nn Automotive Head Lamps/Running Lamps
nn High Power LED Lighting
LT8391
60V Synchronous 4-Switch
Buck-Boost LED Controller
with Spread Spectrum
DESCRIPTION
The LT®8391 is a synchronous 4-switch buck-boost LED
controller that regulates LED current from input voltage
above, below, or equal to the output voltage. The propri-
etary peak-buck peak-boost current mode control scheme
allows adjustable and synchronizable 150kHz to 650kHz
fixed frequency operation, or internal ±15% triangle spread
spectrum operation for low EMI. With 4V to 60V input, 0V
to 60V output, and seamless low noise transitions between
operation regions, the LT8391 is ideal for LED driver and
battery charger applications in automotive, industrial, and
battery-powered systems.
The LT8391 provides both internal (up to 128:1) and
external (up to 2000:1) LED current PWM dimming with
a high-side PMOS switch. Two CTRL pins provide flexible
20:1 analog dimming with ±3% LED current accuracy at
100mV full scale. Fault protection is provided to detect
an open or short LED condition, during which the LT8391
retries, latches off, or keeps running.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
98% Efficient 50W (25V, 2A) Buck-Boost LED Driver
VIN
6V TO 55V
499k
221k
FAULT
100k
0.47µF 100k
ANALOG DIM
PWM DIM
100k
400kHz
2.2k
10nF
33µF
63V
EN/UVLO VIN
INTVCC
4.7µF
FAULT
VREF LT8391
CTRL2
BST1
TG1
SW1
LSP
LSN
BG1
CTRL1
PWM
RP
SYNC/SPRD
RT
VSSC
0.1µF
GND
BG2
SW2
TG2
BST2
FB
VOISUPT
ISN
PWMTG
8391 TA01a
4.7µF
100V
x2
10µF
50V
x2
0.1µF 0.1µF
0.004Ω 10µH
5.1Ω
1M
34.8k
0.05Ω
25V
2A
LED
For more information www.linear.com/LT8391
Efficiency vs VIN
100
98 BOOST
96
BUCK
94
92 BUCK-BOOST
90
88
86
84
82
80
0 10 20 30 40 50 60
INPUT VOLTAGE (V)
8391 TA01b
8391f
1
1 page  
LT8391
E LECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2). VIN = 12V, VEN/UVLO = 1.5V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX
Current Comparator
Fault
Maximum Current Sense Threshold V(LSP-LSN)
Reverse Current Sense Threshold V(LSP-LSN)
LSP Pin Bias Current
LSN Pin Bias Current
Buck, VFB = 0.8V
Boost, VFB = 0.8V
Buck, VFB = 0.8V
Boost, VFB = 0.8V
VLSP = VLSN = 12V
VLSP = VLSN = 12V
l 35 50 65
l 40 50 60
–4
–4
60
60
FB Overvoltage Threshold (VFB)
FB Overvoltage Hysteresis
Rising
l 1.03 1.05 1.07
l 15 25 35
FB Open LED Threshold (VFB)
FB Open LED Hysteresis
FB Short LED Threshold (VFB)
FB Short LED Hysteresis
Rising, V(ISP-ISN) = 0V
V(ISP-ISN) = 0V
Falling
Hysteresis
l 0.93 0.95 0.97
l 35 50 65
l 0.24 0.25 0.26
l 35 50 65
ISP/ISN Over Current Threshold V(ISP-ISN)
ISP/ISN Open LED Threshold V(ISP-ISN)
ISP/ISN Open LED Hysteresis
FAULT Pull-Down Resistance
VISP = 12V
Falling, VFB = 1.0V
VFB = 1.0V
l8
l3
750
10 12
57
100 200
SS Hard Pull-Down Resistance
SS Pull-Up Current
SS Pull-Down Current
SS Fault Latch-Off Threshold
VEN/UVLO = 1.1V
VFB = 0.8V, VSS = 0V
VFB = 1.0V, VSS = 2V
Falling
100 200
10.5 12.5 14.5
1.05 1.25 1.45
1.7
SS Fault Latch-Off Hysteresis
50
SS Fault Reset Threshold
0.2
Oscillator
RT Pin Voltage
Switching Frequency
SYNC Frequency
RT = 100kΩ
VSYNC/SPRD = 0V, RT = 226k
VVSSYYNNCC//SSPPRRDD
=
=
0V,
0V,
RRTT
=
=
100k
59.0k
1.00
l 190 200 210
l 380 400 420
l 570 600 630
150 650
SYNC/SPRD Input Bias Current
SYNC/SPRD Threshold Voltage
VSYNC/SPRD = 5V
–0.1 0
0.4
0.1
1.5
Highest Spread Spectrum Above Oscillator
Frequency
VSYNC/SPRD = 5V
13.8 14.5 15.2
Lowest Spread Spectrum Below Oscillator
Frequency
VSYNC/SPRD = 5V
–16.5 –15.7 –14.9
UNITS
mV
mV
mV
mV
µA
µA
V
mV
V
mV
V
mV
mV
mV
mV
Ω
Ω
µA
µA
V
mV
V
V
kHz
kHz
kHz
kHz
µA
V
%
%
For more information www.linear.com/LT8391
8391f
5
5 Page 
LT8391
PIN FUNCTIONS
BG1: Buck Side Bottom Gate Drive. Drives the gate of buck
side bottom N-channel MOSFET with a voltage swing from
ground to INTVCC.
BST1: Buck Side Bootstrap Floating Driver Supply. The
BST1 pin has an integrated bootstrap Schottky diode from
the INTVCC pin and requires an external bootstrap capacitor
to the SW1 pin. The BST1 pin swings from a diode voltage
drop below INTVCC to (VIN + INTVCC).
SW1: Buck Side Switch Node. The SW1 pin swings from
a Schottky diode voltage drop below ground up to VIN.
TG1: Buck Side Top Gate Drive. Drives the gate of buck
side top N-channel MOSFET with a voltage swing from
SW1 to BST1.
LSP: Positive Terminal of the Buck Side Inductor Current
Sense Resistor (RSENSE). Ensure accurate current sense
with Kelvin connection.
LSN: Negative Terminal of the Buck Side Inductor Current
Sense Resistor (RSENSE). Ensure accurate current sense
with Kelvin connection.
VIN: Input Supply. The VIN pin must be tied to the power
input to determine the buck, buck-boost, or boost operation
regions. Locally bypass this pin to ground with a minimum
1µF ceramic capacitor.
INTVCC: Internal 5V Linear Regulator Output. The INTVCC
linear regulator is supplied from the VIN pin, and powers
the internal control circuitry and gate drivers. Locally
bypass this pin to ground with a minimum 4.7µF ceramic
capacitor.
EN/UVLO: Enable and Undervoltage Lockout. Force the
pin below 0.3V to shut down the part and reduce VIN qui-
escent current below 2µA. Force the pin above 1.234V for
normal operation. The accurate 1.224V falling threshold
can be used to program an undervoltage lockout (UVLO)
threshold with a resistor divider from VIN to ground. An
accurate 2.5µA pull-down current allows the programming
of VIN UVLO hysteresis. If neither function is used, tie this
pin directly to VIN.
RP: Internal PWM Dimming Frequency Setting. The RP pin
is used to set the internal PWM dimming frequency with
a resistor to ground. Neither uses a resistor larger than
1MΩ nor leaves this pin open. If an external PWM dimming
pulse is available at the PWM pin, tie this pin to ground.
PWM: PWM Dimming Input. The PWM pin can be used
in two ways: external PWM dimming and internal PWM
dimming. For external PWM dimming, drive this pin with
a digital pulse from 0V to a voltage higher than 1.5V to
control PWM dimming of the LED string. Make sure the
RP pin is tied to ground in this case. For internal PWM
dimming, apply an analog voltage between 1V and 2V to
generate an internal digital pulse by comparing with the
internal ramp. If PWM dimming is not used, tie this pin to
INTVCC. Forcing the pin low turns off TG1 and TG2, turns
on BG1 and BG2, disconnects the VC pin from all internal
loads, and turns off PWMTG.
VREF: Voltage Reference Output. The VREF pin provides an
accurate 2V reference capable of supplying 1mA current.
Locally bypass this pin to ground with a 0.47µF ceramic
capacitor.
CTRL1: Control Input for LED Current Sense Threshold. The
CTRL1 pin is used to program the LED regulation current:
ILED
=
Min(VCTRL1
–
0.25V, VCTRL2
10 •RLED
–
0.25,1V)
The VCTRL1 can be set by an external voltage reference
or a resistor divider from VREF to ground. For 0.25V ≤
VCTRL1 ≤ 1.15V, the current sense threshold linearly goes
up from 0mV to 90mV. For VCTRL1 ≥ 1.35V, the current
sense threshold is constant at 100mV full scale value.
For 1.15V ≤ VCTRL1 ≤ 1.35V, the current sense threshold
smoothly transitions from the linear function of VCTRL1
to the 100mV constant value. Tie CTRL1 to VREF for the
100mV full scale threshold. Force the pin below 0.2V to
stop switching.
ISP: Positive Terminal of the LED Current Sense Resistor
(RLED). Ensure accurate current sense with Kelvin con-
nection.
ISN: Negative Terminal of the LED Current Sense Resis-
tor (RLED). Ensure accurate current sense with Kelvin
connection.
For more information www.linear.com/LT8391
8391f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LT8391.PDF ] | |
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