|
|
PDF LTC3858-2 Data sheet ( Hoja de datos )
| Número de pieza | LTC3858-2 | |
| Descripción | Dual 2-Phase Synchronous Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC3858-2 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
|
No Preview Available !
FEATURES
n Low Operating IQ: 170μA (One Channel On)
n Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
n Wide VIN Range: 4V to 38V
n RSENSE or DCR Current Sensing
n Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
n OPTI-LOOP® Compensation Minimizes COUT
n Phase-Lockable Frequency (75kHz-850kHz)
n Programmable Fixed Frequency (50kHz-900kHz)
n Selectable Continuous, Pulse-Skipping or
Burst Mode® Operation at Light Loads
n Very Low Dropout Operation: 99% Duty Cycle
n Adjustable Output Voltage Soft-Start or Tracking
n Power Good Output Voltage Monitor
n Low Shutdown IQ: 8μA
n Internal LDO Powers Gate Drive from VIN or EXTVCC
n No Current Foldback During Start-Up
n 5mm × 5mm QFN Package
APPLICATIONS
n Automotive Systems
n Battery Operated Digital Devices
n Distributed DC Power Systems
LTC3858-2
Low IQ, Dual
2-Phase Synchronous
Step-Down Controller
DESCRIPTION
The LTC®3858-2 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows a phase-lockable fre-
quency of up to 850kHz. Power loss and noise due to the
input capacitor ESR are minimized by operating the two
controller outputs out of phase.
The 170μA no-load quiescent current extends operating
life in battery-powered systems. OPTI-LOOP compensa-
tion allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
LTC3858-2 differs from the LTC3858 by having the overvolt-
age protection crowbar and short-circuit latchoff disabled.
A wide 4V to 38V input supply range encompasses a wide
range of intermediate bus voltages and battery chemistries.
Independent soft-start pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, μModule, PolyPhase, Linear Technology and the Linear
logo are registered trademarks and No RSENSE and UltraFast are trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by U.S.
Patents, including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
TYPICAL APPLICATION
VOUT1
3.3V
5A
High Efficiency Dual 8.5V/3.3V Step-Down Converter
3.3μH
0.007Ω
62.5k
150μF
0.1μF
VIN
TG1
INTVCC
TG2
BOOST1
BOOST2
SW1 SW2
BG1 BG2
LTC3858-2
PGND
SENSE1+
SENSE2+
680pF
SENSE1–
VFB1
ITH1
SS1
SGND
SENSE2–
VFB2
ITH2
SS2
20k 15k
0.1μF
0.1μF
4.7μF
0.1μF
680pF
15k
VIN
22μF 9V TO 38V
50V
7.2μH
0.01Ω
193k
20k
VOUT2
8.5V
3.5A
150μF
38582 TA01a
Efficiency and Power Loss
vs Load Current
100 10000
90
80
EFFICIENCY
70
1000
60 100
POWER LOSS
50
40 10
30
20
10
0
0.0001
0.001 0.01
VIN = 12V
1
VOUT = 3.3V
FIGURE 13 CIRCUIT
0.1
0.1 1 10
OUTPUT CURRENT (A)
38582 TA01b
38582f
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3858-2
Efficiency and Power Loss
vs Output Current
100
FIGURE 13 CIRCUIT
90 VIN = 12V
80 VOUT = 3.3V
10000
1000
70
60 100
50
40
30
20
10
0
0.0001
0.001 0.01
Burst Mode
OPERATION 10
PULSE-
SKIPPING
MODE
FORCED
1
CONTINUOUS
MODE
0.1
0.1 1 10
OUTPUT CURRENT (A)
38582 G01
Load Step (Burst Mode Operation)
Efficiency vs Output Current
100
90
VIN = 5V
80
70
VIN = 12V
60
50
40
30
20
10
0
0.0001
VOUT = 3.3V
FIGURE 13 CIRCUIT
0.001 0.01 0.1
1
OUTPUT CURRENT (A)
10
38582 G02
Load Step
(Forced Continuous Mode)
Efficiency vs Input Voltage
98
FIGURE 13 CIRCUIT
96 VOUT = 3.3V
IOUT = 4A
94
92
90
88
86
84
82
80
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
38582 G03
Load Step (Pulse-Skipping Mode)
VOUT
100mV/DIV
AC-
COUPLED
VOUT
100mV/DIV
AC-
COUPLED
VOUT
100mV/DIV
AC-
COUPLED
IL
2A/DIV
IL
2A/DIV
IL
2A/DIV
VOUT = 3.3V
20μs/DIV
FIGURE 13 CIRCUIT
38582 G04
Inductor Current at Light Load
VOUT = 3.3V
20μs/DIV
FIGURE 13 CIRCUIT
Soft-Start
38585 G05
VOUT = 3.3V
20μs/DIV
FIGURE 13 CIRCUIT
Tracking Start-Up
38582 G06
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
2A/DIV
PULSE-
SKIPPING
MODE
VOUT = 3.3V
2μs/DIV
ILOAD = 200μA
FIGURE 13 CIRCUIT
VOUT2
2V/DIV
VOUT1
2V/DIV
VOUT2
2V/DIV
VOUT1
2V/DIV
38582 G07
20ms/DIV
FIGURE 13 CIRCUIT
38582 G08
20ms/DIV
FIGURE 13 CIRCUIT
38572 G09
38582f
5
5 Page 
LTC3858-2
OPERATION (Refer to the Functional Diagram)
Table 1 summarizes the differences between the LTC3858-2
and its sister parts, the LTC3858 and LTC3858-1. The
LTC3858-2 uses a constant frequency, current mode
step-down architecture with the two controller channels
operating 180 degrees out of phase. During normal op-
eration, each external top MOSFET is turned on when the
clock for that channel sets the RS latch, and is turned off
when the main current comparator, ICMP, resets the RS
latch. The peak inductor current at which ICMP trips and
resets the latch is controlled by the voltage on the ITH pin,
which is the output of the error amplifier, EA. The error
amplifier compares the output voltage feedback signal at
the VFB pin (which is generated with an external resistor
divider connected across the output voltage, VOUT, to
ground) to the internal 0.800V reference voltage. When the
load current increases, it causes a slight decrease in VFB
relative to the reference, which causes the EA to increase
the ITH voltage until the average inductor current matches
the new load current.
After the top MOSFET is turned off each cycle, the bottom
MOSFET is turned on until either the inductor current starts
to reverse, as indicated by the current comparator IR, or
the beginning of the next clock cycle.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTVCC pin. When
the EXTVCC pin is left open or tied to a voltage less than
4.7V, the VIN LDO (low dropout linear regulator) supplies
5.1V from VIN to INTVCC. If EXTVCC is taken above 4.7V,
the VIN LDO is turned off and the EXTVCC LDO is turned
on. Once enabled, the EXTVCC LDO supplies 5.1V from
EXTVCC to INTVCC. Using the EXTVCC pin allows the INTVCC
power to be derived from a high efficiency external source
such as one of the LTC3858-2 switching regulator outputs.
Each top MOSFET driver is biased from the floating boot-
strap capacitor, CB, which normally recharges during each
switching cycle through an external diode when the top
MOSFET turns off. If the input voltage, VIN, decreases to
a voltage close to VOUT, the loop may enter dropout and
attempt to turn on the top MOSFET continuously. The
dropout detector detects this and forces the top MOSFET
off for about one-twelfth of the clock period every tenth
cycle to allow CB to recharge.
Table 1. Summary of the Differences Between LTC3858, LTC3858-1 and LTC3858-2
LTC3858
LTC3858-1
Short-Circuit Latchoff Feature?
Yes, But Can Be Defeated
Yes, But Can Be Defeated
Overvoltage Protection
Optional Tracking Start-Up?
BG Forced On
(Bottom MOSFET “Crowbar”)
No
BG Forced On
(Bottom MOSFET “Crowbar”)
No
Independent PGOOD1 and PGOOD2 Pins?
Yes
No, PGOOD1 Only
CLKOUT/PHASMD Pins for PolyPhase
Yes
No
Adjustable Current Limit (ILIM Pin)
Package
Yes
5mm × 5mm QFN
No
4mm × 5mm QFN and
Narrow SSOP
LTC3858-2
Not Present
BG Not Forced On
(Behavior Depends on Light Load Mode)
Yes
Yes
Yes
Yes
5mm × 5mm QFN
38582f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3858-2.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC3858-1 | Dual 2-Phase Synchronous Step-Down Controller |  Linear Technology Corporation |
| LTC3858-2 | Dual 2-Phase Synchronous Step-Down Controller | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |