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PDF LTC3855 Data sheet ( Hoja de datos )
| Número de pieza | LTC3855 | |
| Descripción | Multiphase Synchronous DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3855
Dual, Multiphase
Synchronous DC/DC Controller
with Differential Remote Sense
Features
Description
n Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
n High Efficiency: Up to 95%
n RSENSE or DCR Current Sensing
n Programmable DCR Temperature Compensation
n ±0.75% 0.6V Output Voltage Accuracy
n Phase-Lockable Fixed Frequency 250kHz to 770kHz
n True Remote Sensing Differential Amplifier
n Dual N-Channel MOSFET Synchronous Drive
n Wide VIN Range: 4.5V to 38V
n VOUT Range: 0.6V to 12.5V without Differential Amplifier
n VOUT Range: 0.6V to 3.3V with Differential Amplifier
n Clock Input and Output for Up to 12-Phase Operation
n Adjustable Soft-Start or VOUT Tracking
n Foldback Output Current Limiting
n Output Overvoltage Protection
n 40-Pin (6mm × 6mm) QFN and 38-Lead FE Packages
Applications
n Computer Systems
n Telecom Systems
wwwn.D aItanSdhuesettr4iUa.lcoamnd Medical Instruments
n DC Power Distribution Systems
The LTC®3855 is a dual PolyPhase® current mode synchro-
nous step-down switching regulator controller that drives
all N-channel power MOSFET stages. It includes a high
speed differential remote sense amplifier. The maximum
current sense voltage is programmable for either 30mV,
50mV or 75mV, allowing the use of either the inductor DCR
or a discrete sense resistor as the sensing element.
The LTC3855 features a precision 0.6V reference and can
produce output voltages up to 12.5V. A wide 4.5V to 38V
input supply range encompasses most intermediate bus
voltages and battery chemistries. Power loss and supply
noise are minimized by operating the two controller output
stages out of phase. Burst Mode® operation, continuous
or pulse-skipping modes are supported.
The LTC3855 can be configured for up to 12-phase op-
eration, has DCR temperature compensation, two power
good signals and two current limit set pins. The LTC3855
is available in low profile 40-pin 6mm × 6mm QFN and
38-lead exposed pad FE packages.
L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and PolyPhase are registered
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
High Efficiency Dual 1.8V/1.2V Step-Down Converter
0.56µH
VOUT1
1.8V
15A
+
40.2k
330µF
×2
+
4.7µF
0.1µF
VIN
TG1
BOOST1
SW1
INTVCC
TG2
BOOST2
SW2
BG1 BG2
PGND1
SENSE1+
SENSE1–
LTC3855
PGND2
FREQ
SENSE2+
SENSE2–
DIFFOUT
VFB1
VFB2
470pF
ITH1 ITH2
TK/SS1 DIFFP SGND DIFFN TK/SS2
20k 15k 0.1µF
0.1µF
1µF
0.1µF
20k
470pF
100k 7.5k
20k
22µF
VIN
4.5V TO
20V
0.4µH
Load Step
(Forced Continuous Mode)
ILOAD
5A/DIV
300mA TO 5A
IL
5A/DIV
VOUT2
1.2V
15A
+ 330µF
×2
3855 TA01
VOUT
100mV/DIV
AC-COUPLED
VIN = 12V
VOUT = 1.8V
50µs/DIV
3855 TA01a
3855f
1 page  
LTC3855
E lectrical Characteristics The l denotes the specifications which apply over the full operating
junction temperature range (E-Grade), otherwise specifications are at TA = 25°C. VIN = 15V, VRUN/SS = 5V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
On Chip Driver
TG RUP
TG RDOWN
BG RUP
BG RDOWN
TG Pull-Up RDS(ON)
TG Pull-Down RDS(ON)
BG Pull-Up RDS(ON)
BG Pull-Down RDS(ON)
TG High
TG Low
BG High
BG Low
2.6 Ω
1.5 Ω
2.4 Ω
1.1 Ω
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3855E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3855I is guaranteed
to meet performance specifications over the full –40°C to 125°C operating
junction temperature range.
Note 3: TJ is calculated from the ambient temperature TA and power
dissipation PD according to the following formulas:
LTC3855UJ: TJ = TA + (PD • 33°C/W)
LTC3855FE: TJ = TA + (PD • 25°C/W)
Note 4: The LTC3855 is tested in a feedback loop that servos VITH1,2 to a
specified voltage and measures the resultant VFB1,2.
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6: Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7: The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥40% of IMAX (see Minimum On-Time
Considerations in the Applications Information section).
Note 8: Guaranteed by design.
Typical Performance Characteristics
Efficiency vs Output Current
and Mode
100
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80 OPERATION
70
60 DCM
50
VIN = 12V
VOUT = 1.8V
40 CCM
30
20
10
0
0.01
CIRCUIT OF FIGURE 19
0.1 1 10
LOAD CURRENT (A)
100
3855 G23
Efficiency vs Output Current
and Mode
100
90
80
Burst Mode
OPERATION
70
60
50 DCM
VIN = 12V
VOUT = 1.2V
40 CCM
30
20
10
0
0.01
CIRCUIT OF FIGURE 19
0.1 1
10
LOAD CURRENT (A)
100
3855 G24
Full Load Efficiency and Power
Loss vs Input Voltage
90
1.8V
EFFICIENCY
1.2V
85
5
4
1.8V
80 POWER LOSS
1.2V
3
75 CIRCUIT OF FIGURE 19
5 10
15
INPUT VOLTAGE (V)
2
20
3855 G24
3855f
5 Page 
Functional Block Diagram
FREQ
MODE/PLLIN
PHASMD
ITEMP
PLL-SYNC
MODE/SYNC
DETECT
TEMPSNS
0.6V
–+
F
EXTVCC
4.7V
–+
F
5V
REG
CLKOUT
OSC
+
ICMP
–
3k
S
RQ
–
IREV
+
FCNT
BURSTEN
ON SWITCH
LOGIC
AND
ANTI-
SHOOT
THROUGH
RUN
OV
ILIM SLOPE COMPENSATION
INTVCC
UVLO
1 SLOPE RECOVERY
51k ACTIVE CLAMP
ITHB
LTC3855
VIN
VIN
+
CIN
INTVCC
BOOST
TG CB
SW
SENSE+ DB
SENSE–
BG
CVCC
PGND
PGOOD
+
UV
–
0.54V
VFB
R2
INTVCC
M1
L1
VOUT
+
COUT
M2
DIFFP
+
DIFFAMP
–
40k
40k
VIN SLEEP
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REF
–+
0.55V
EA
– SS +
0.5V
– RUN +
1.2V
1.2µA
+
OV
–
0.66V
SGND
R1
1µA
40k 40k DIFFN
ITH RC CC1
RUN
TK/SS
CSS
3855 FBD
DIFFOUT
3855f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3855.PDF ] | |
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