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PDF LT3840 Data sheet ( Hoja de datos )
| Número de pieza | LT3840 | |
| Descripción | Wide Input Range Synchronous Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
LT3840
Wide Input Range
Synchronous Regulator Controller
with Accurate Current Limit
Description
n Wide Input Range: 2.5V to 60V
n Integrated Buck-Boost Supply for 7.5V MOSFET
Gate Drive
n Programmable Constant-Current Operation with
Current Monitor Output
n Low IQ: 75µA, 12VIN to 3.3VOUT
n Selectable Low Output Ripple Burst Mode®
Operation
n VOUT Up to 60V
n Adjustable and Synchronizable: 50kHz to 1MHz
n Internal OVLO Protects for Input Transients Up to 80V
n Accurate Input Overvoltage and Undervoltage Threshold
n Programmable Soft-Start with Voltage Tracking
n Power Good and Output OVP
n 28-Lead TSSOP and 38-Lead 4mm × 6mm QFN Packages
Applications
n Automotive Supplies
n Industrial Systems
n Distributed DC Power Systems
The LT®3840 is a high voltage synchronous step-down
switching regulator controller capable of operating from
a 2.5V to 60V supply.
The LT3840’s low quiescent current, when configured for
user selectable Burst Mode operation, helps extend run
time in battery-powered systems by increasing efficiency
at light loads. The LT3840 uses a constant frequency,
current mode architecture. High current applications are
possible with large N-channel gate drivers capable of
driving multiple low RDS(ON) MOSFETs.
An integrated buck-boost switching regulator generates
a 7.5V bias supply voltage for MOSFET gate drive and IC
power allowing higher efficiency operation over the entire
input voltage range and eliminating the need for an external
bias voltage. An accurate current limit set point regulates
the maximum output current. A current monitor reports
the average output current.
L, LT, LTC, LTM, Linear Technology, Burst Mode, and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
Typical Application
VIN
4V TO 60V
High Efficiency Synchronous Step-Down Converter
68µF 1µF 33µH
×2
49.9k
AUXBST AUXSW1
EN
VIN
AUXVIN
UVLO
LT3840
AUXSW2
INTVCC
BOOST
OVLO
TG
PG SW
SYNC
BG
20k
1500pF
MODE
RT SENSE+
VC SENSE–
TK/SS
FB
100pF
IMON
ICOMP
GND
ICTRL
2200pF
7.68k
470pF
4.7µF
1µF
1.5µH
16.9k
10k
2m
VOUT
3.3V
20A
330µF
×2
3840 TA01a
12VIN to 3.3VOUT Efficiency
100
95
90
85
80
75
70
65
60
55
50
0
5 10 15
LOAD CURRENT (A)
20
3840 TA01b
For more information www.linear.com/LT3840
3840fa
1
1 page  
LT3840
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
EN Threshold Voltage vs
Temperature
1.40
1.35
1.30
1.25 EN RISING
1.20
1.15 EN FALLING
1.10
1.05
1.00
95
90
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G01
UVLO Threshold Voltage vs
Temperature
1.40
1.35
1.30
UVLO RISING
1.25
1.20
1.15 UVLO FALLING
1.10
1.05
1.00
95
90
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G02
OVLO Threshold vs Temperature
1.30
OVLO RISING
1.25
1.20
1.15 OVLO FALLING
1.10
1.05
1.00
0.95
0.90
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G03
Shutdown Current vs Temperature
20
18
16
14
12
10
8
6
4
2
VIN
AUXVIN
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G04
Switching Frequency vs
Temperature
330
RT = 49.9k
320
310
300
290
280
270
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G07
INTVCC Regulation Voltage vs
Temperature
7.7
7.6
7.5
7.4
7.3
7.2
7.1
7.0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G05
Soft-Start (TK/SS) Current vs
Temperature
12
11
10
9
8
7
6
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G08
ISENSE+ + ISENSE– vs VSENSE(CM)
1600
1200
800
400
0
–400
–800
0
1 2 3 45
COMMON MODE SENSE VOLTAGE (V)
3840 G06
Regulated FB Voltage vs
Temperature
1.28
1.27
1.26
1.25
1.24
1.23
1.22
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3840 G09
For more information www.linear.com/LT3840
3840fa
5
5 Page 
LT3840
Operation
low. The VC voltage is the DC control node that sets the
peak inductor current. A resistor and capacitor on ICOMP
compensate the current control loop. Figure 2 includes
the block diagram of the average current control loop
and transfer functions showing the relationship between
VSENSE, ICTRL and IMON.
Auxiliary Bias Supply
The LT3840 wide input voltage range is made possible
with the auxiliary bias supply switching regulator. Other
switching regulator controllers typically use a linear volt-
age regulator to provide the gate drive voltage from VIN.
This approach is limited by power dissipation at high
input voltage and dropout at low voltage. The LT3840
bias regulator efficiently generates a 7.5V bias voltage,
capable of adequately driving large multiple MOSFETs, at
input voltages as low as 2.5V and as high as 60V.
The auxiliary bias supply is a monolithic buck-boost, peak
current mode topology. The switching frequency is fixed
and synchronized with the LT3840 synchronous buck con-
troller. The switching regulator is internally compensated
RSENSE
SW VOUT
SENSE+
+
COUT
VC
+
ICOMP GM –– 1V – +
20x
–
SENSE–
ICTRL
IMON
MAXIMUM
AVERAGE
CURRENT
CONTROL
50
40 TRANSFER FUNCTION
MAX. AVG. SENSE VOLTAGE
vs ICTRL
30
20
10
0
0 100 200 300 400 500 600 700 800 900 1000
VICTRL (mV)
1000
900
800
700
600
500
400
300
200
100
0
0
TRANSFER FUNCTION
IMON vs AVG.
SENSE VOLTAGE
10 20 30
VSENSE (mV)
40
Figure 2. Average Output Current Limit Functional Block Diagram and Transfer Curves
50
3840 F02
For more information www.linear.com/LT3840
3840fa
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT3840.PDF ] | |
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