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PDF LTC3812-5 Data sheet ( Hoja de datos )
| Número de pieza | LTC3812-5 | |
| Descripción | 60V Current Mode Synchronous Switching Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURESwww.datasheet4u.com
n High Voltage Operation: Up to 60V
n Large 1Ω Gate Drivers
n No Current Sense Resistor Required
n Dual N-Channel MOSFET Synchronous Drive
n Extremely Fast Transient Response
n ±0.5% 0.8V Voltage Reference
n Programmable Soft-Start
n Generates 5.5V Driver Supply
n Selectable Pulse Skip Mode Operation
n Power Good Output Voltage Monitor
n Adjustable On-Time/Frequency: tON(MIN) < 100ns
n Adjustable Cycle-by-Cycle Current Limit
n Undervoltage Lockout On Driver Supply
n Output Overvoltage Protection
n Thermally Enhanced 16-Pin TSSOP Package
APPLICATIONS
n 48V Telecom and Base Station Power Supplies
n Networking Equipment, Servers
n Automotive and Industrial Control Systems
LTC3812-5
60V Current Mode
Synchronous Switching
Regulator Controller
DESCRIPTION
The LTC3812-5 is a synchronous step-down switching
regulator controller that can directly step down voltages
from up to 60V input, making it ideal for telecom and
automotive applications. The LTC3812-5 uses a constant
on-time valley current control architecture to deliver very
low duty cycles with accurate cycle-by-cycle current limit
without requiring a sense resistor.
A precise internal reference provides 0.5% DC accuracy.
A high bandwidth (25MHz) error amplifier provides very
fast line and load transient response. Large 1Ω gate driv-
ers allow the LTC3812-5 to drive large power MOSFETs
for higher current applications. The operating frequency
is selected by an external resistor and is compensated for
variations in VIN. A shutdown pin allows the LTC3812-5 to
be turned off reducing the supply current to <230μA.
Integrated bias control generates gate drive power from
the input supply during start-up and when an output short-
circuit occurs, with the addition of a small external SOT23
MOSFET. When in regulation, power is derived from the
output for higher efficiency.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5847554, 6304066, 6476589, 6580258, 6677210, 6774611.
TYPICAL APPLICATION
High Efficiency High Voltage Step-Down Converter
RON
110k
PGOOD
100k
1000pF
47pF
200k
5pF
ION NDRV
PGOOD
BOOST
LTC3812-5
VRNG
TG
FCB
RUN/SS
SW
EXTVCC
INTVCC
ITH BG
VFB SGND PGND
100k
M3
ZXMN-
10A07F
0.1μF
1μF
VIN
+ 6V TO 60V
CIN
22μF
M1
Si7850DP
L1
4.7μH
M2
Si7850DP
D1 10k +
MBR1100
1.89k
VOUT
5V
5A
COUT
270μF
38125 TA01
Efficiency vs Load Current
100
VIN = 12V
95
VIN = 42V
90 VIN = 24V
85
80
0
12 34
LOAD CURRENT (A)
56
38125 TA01b
38125fb
1
1 page  
LTC3812-5
TYPICAL PERFORMANCE CHARACTERISTICS
Load Transient Response
Start-Up
Short-Circuit/Fault Timeout
Operation
www.datasheet4u.com
VOUT
50mV/DIV
IOUT
5A/DIV
10μs/DIV
FRONT PAGE CIRCUIT
VIN = 25V
0A TO 5A LOAD STEP
38125 G01
VIN
20V/DIV
INTVCC,
VOUT
2V/DIV
INTVCC
VOUT
IL
2A/DIV
2ms/DIV
FRONT PAGE CIRCUIT
VIN = 30V
ILOAD = 0.5A
FCB = 0V
VOUT
5V/DIV
SS/TRACK
2V/DIV
IL
5A/DIV
38125 G02
5ms/DIV
FRONT PAGE CIRCUIT
VIN = 25V
RSHORT = 0.1Ω
38125 G03
Short-Circuit/Foldback Operation
Pulse Skip Mode Operation
VOUT
5V/DIV
IL
5A/DIV
200μs/DIV
FRONT PAGE CIRCUIT
VIN = 25V
VOUT
100mV/DIV
ITH
0.5A/DIV
IL
2A/DIV
38125 G04
20μs/DIV
FRONT PAGE CIRCUIT
VIN = 25V
IOUT = 100mA
FCB = INTVCC
38125 G05
Efficiency vs Input Voltage
100
FRONT PAGE CIRCUIT
f = 250kHz
95 ILOAD = 5A
FORCED
CONTINUOUS
90
ILOAD = 0.5A
FORCED
CONTINUOUS
ILOAD = 0.5A
85 PULSE SKIP
80
0
10 20 30 40 50
INPUT VOLTAGE (V)
60
38125 G06
Efficiency vs Load Current
100
VIN = 24V
95 VIN = 42V
90
VOUT = 12V
FCB = INTVCC
f = 250kHz
85
012 34
LOAD CURRENT (A)
56
38125 G07
Frequency vs Input Voltage
300
FRONT PAGE CIRCUIT
290 FCB = 0V
280
LOAD = 5A
270
260
250
240 LOAD = 0A
230
220
210
200
0
10 20 30 40 50 60
INPUT VOLTAGE (V)
LT1108 • TPC12
Frequency vs Load Current
350
FRONT PAGE CIRCUIT
300 FORCED
CONTINUOUS
250
200
PULSE SKIP
150
100
50
0
012345
LOAD CURRENT (A)
38125 G09
38125fb
5
5 Page 
LTC3812-5
OPERATION
Main Control Loop
The LTC3812-5 is a current mode controller for DC/DC
wwws.dtaetpas-hdeoewt4nu.cocmonverters. In normal operation, the top
MOSFET is turned on for a fixed interval determined by
a one-shot timer (OST). When the top MOSFET is turned
off, the bottom MOSFET is turned on until the current
comparator ICMP trips, restarting the one-shot timer and
initiating the next cycle. Inductor current is determined by
sensing the voltage between the PGND and SW pins using
the bottom MOSFET on-resistance. The voltage on the ITH
pin sets the comparator threshold corresponding to the
inductor valley current. The fast 25MHz error amplifier EA
adjusts this voltage by comparing the feedback signal VFB
to the internal 0.8V reference voltage. If the load current
increases, it causes a drop in the feedback voltage relative
to the reference. The ITH voltage then rises until the average
inductor current again matches the load current.
The operating frequency is determined implicitly by the top
MOSFET on-time and the duty cycle required to maintain
regulation. The one-shot timer generates an on time that is
proportional to the ideal duty cycle, thus holding frequency
approximately constant with changes in VIN. The nominal
frequency can be adjusted with an external resistor RON.
Pulling the RUN/SS pin low forces the controller into its
shutdown state, turning off both M1 and M2. Forcing a
voltage above 1.5V will turn on the device.
Pulse Skip Mode
The LTC3812-5 can operate in one of two modes selectable
with the FCB pin—pulse skip mode or forced continuous
mode (see Figure 1). Pulse skip mode is selected when
increased efficiency at light loads is desired (see Figure 2).
In this mode, the bottom MOSFET is turned off when
inductor current reverses to minimize efficiency loss due
to reverse current flow and gate charge switching. At low
load currents, ITH will drop below the zero current level
(1.2V) shutting off both switches. Both switches will
remain off with the output capacitor supplying the load
current until the ITH voltage rises above the zero current
100
PULSE
90 SKIP
80
70
60
50
40
30
20
10
0
0.01
FORCED
CONTINUOUS
0.1 1
LOAD (A)
VIN = 12V
VIN = 42V
10
38125 F02
Figure 2. Efficiency in Pulse Skip/Forced Continuous Modes
PULSE SKIP MODE
FORCED CONTINUOUS
DECREASING
LOAD
CURRENT
0A
0A
0A
0A
0A 0A
38125 F01
Figure 1. Comparison of Inductor Current Waveforms for Pulse Skip Mode
and Forced Continuous Operation
38125fb
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3812-5.PDF ] | |
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