LT3850-1 Datasheet PDF - Linear Technology

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LT3850-1
Linear Technology

Part Number LT3850-1
Description 2-Phase Synchronous Step-Down Switching Controller
Page 30 Pages


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FEATURES
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 ±1% 0.8V Output Voltage Accuracy
n Phase-Lockable Fixed Frequency 250kHz to 780kHz
n Supports Pre-Biased Output
n Dual N-Channel MOSFET Synchronous Drive
n Wide VIN Range: 4V to 24V (30V for LTC3850I)
Operation
n Adjustable Soft-Start Current Ramping or Tracking
n Foldback Output Current Limiting
n Output Overvoltage Protection
n Power Good Output Voltage Monitor
n 28-Pin 4mm × 4mm, 4mm × 5mm QFN and Narrow
SSOP Packages
APPLICATIONS
n Notebook and Palmtop Computers
n Portable Instruments
n Battery-Operated Digital Devices
n DC Power Distribution Systems
L, LT, LTC, LTM, OPTI-LOOP and Burst Mode 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.
LTC3850/LTC3850-1
Dual, 2-Phase
Synchronous Step-Down
Switching Controller
DESCRIPTION
The LTC®3850 is a high performance dual synchronous
step-down switching regulator controller that drives all
N-channel power MOSFET stages. A constant-frequency
current mode architecture allows a phase-lockable fre-
quency of up to 780kHz. Power loss and supply noise are
minimized by operating the two controller output stages
out of phase.
OPTI-LOOP® compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The LTC3850 features a precision 0.8V
reference and a power good output indicator. A wide 4V to
24V (28V maximum/30V for LTC3850I) input supply range
encompasses most battery chemistries and intermediate
bus voltages.
Independent TK/SS pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit condi-
tions. The MODE/PLLIN pin selects among Burst Mode®
operation, pulse-skipping mode, or continuous inductor
current mode and allows the IC to be synchronized to an
external clock.
The LTC3850 is available in low profile 28-pin 4mm × 4mm,
4mm × 5mm QFN and narrow SSOP packages.
TYPICAL APPLICATION
VOUT1
3.3V
5A
High Efficiency Dual 3.3V/2.5V Step-Down Converter
2.2µH
2.2k
63.4k
100µF
6V
0.1µF
VIN PGOOD INTVCC
TG1 TG2
500kHz
BOOST1
BOOST2
SW1
LTC3850
BG1
SW2
BG2
MODE/PLLIN
PGND
ILIM FREQ/PLLFLTR
0.1µF
SENSE1+
RUN1
SENSE1
VFB1
SENSE2+
RUN2
SENSE2
VFB2
ITH1 ITH2
220pF
TK/SS1 SGND TK/SS2
20k 15k
0.1µF
0.1µF
4.7µF
0.1µF
22µF
50V
2.2µH
2.2k
0.1µF
10nF
10k
220pF
43.2k
15k 20k
VIN
7V TO
24V
VOUT2
2.5V
5A
100µF
6V
38501 TA01
Efficiency
100
95
VIN = 12V
VOUT = 3.3V
90
EFFICIENCY
85
80
75
70
65 POWER LOSS
60
55
50
10
100 1000
LOAD CURRENT (mA)
10000
1000
100
10
10000
38501 TA01b
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LTC3850/LTC3850-1
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage (VIN).......................... 28V to –0.3V
Input Supply Voltage (VIN),
LTC3850I Only........................................ 30V to –0.3V
Input Supply Transient Voltage (VIN) < 500ms, with
INTVCC ≥ 5V, LTC3850I Only.................... 34V to –0.3V
Top Side Driver Voltages
BOOST1, BOOST2................................... 34V to –0.3V
Switch Voltage (SW1, SW2).......................... 28V to –5V
Switch Voltage (SW1, SW2),
LTC3850I Only........................................... 30V to –5V
INTVCC, RUN1, RUN2, PGOOD, EXTVCC,
(BOOST1-SW1), (BOOST2-SW2).................. 6V to –0.3V
SENSE1+, SENSE2+, SENSE1,
SENSE2Voltages...................................... 5.5V to –0.3V
MODE/PLLIN, ILIM,TK/SS1,TK/SS2, FREQ/PLLFLTR
Voltages................................................. INTVCC to –0.3V
ITH1, ITH2, VFB1, VFB2 Voltages................... 2.7V to –0.3V
INTVCC Peak Output Current.................................100mA
Operating Temperature Range (Note 2)....–40°C to 85°C
Junction Temperature (Note 3).............................. 125°C
Storage Temperature Range....................–65°C to 125°C
Lead Temperature (Soldering, 10 sec)
(GN Package)..................................................... 300°C
PIN CONFIGURATION
TOP VIEW
RUN1
SENSE1+
SENSE1
1
2
3
TK/SS1 4
ITH1
VFB1
SGND
5
6
7
VFB2
ITH2
TK/SS2
SENSE2
SENSE2+
8
9
10
11
12
RUN2 13
ILIM (EXTVCC)* 14
28 FREQ/PLLFLTR
27 MODE/PLLIN
26 SW1
25 TG1
24 BOOST1
23 BG1
22 VIN
21 INTVCC
20 BG2
19 PGND
18 BOOST2
17 TG2
16 SW2
15 PGOOD
GN PACKAGE
28-LEAD NARROW PLASTIC SSOP
TJMAX = 125°C, θJA = 95°C/W
*PIN 14 = ILIM FOR LTC3850GN, EXTVCC FOR LTC3850GN-1
TOP VIEW
TOP VIEW
TK/SS1
ITH1
VFB1
VFB2
ITH2
TK/SS2
SENSE2
1
2
3
4
5
6
7
28 27 26 25 24 23 22
21 BOOST1
20 BG1
19 VIN
29 18 INTVCC
17 BG2
16 PGND
15 BOOST2
8 9 10 11 12 13 14
UF PACKAGE
28-LEAD (4mm × 4mm) PLASTIC QFN
TJMAX = 125°C, θJA = 37°C/W, θJC = 2.6°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
2
28 27 26 25 24 23
SENSE11
22 BOOST1
TK/SS1 2
21 BG1
ITH1 3
20 VIN
VFB1 4
VFB2 5
29 19 INTVCC
18 BG2
ITH2 6
17 PGND
TK/SS2 7
SENSE28
16 BOOST2
15 TG2
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W, EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
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LTC3850/LTC3850-1
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
LTC3850EGN#PBF
LTC3850EGN#TRPBF
LTC3850GN
28-Lead Narrow Plastic SSOP
LTC3850EGN-1#PBF
LTC3850EGN-1#TRPBF LTC3850GN-1
28-Lead Narrow Plastic SSOP
LTC3850IGN#PBF
LTC3850IGN#TRPBF
LTC3850GN
28-Lead Narrow Plastic SSOP
LTC3850IGN-1#PBF
LTC3850IGN-1#TRPBF LTC3850GN-1
28-Lead Narrow Plastic SSOP
LTC3850EUF#PBF
LTC3850EUF#TRPBF
3850
28-Lead (4mm × 4mm) Plastic QFN
LTC3850EUFD#PBF
LTC3850EUFD#TRPBF 3850
28-Lead (4mm × 5mm) Plastic QFN
LTC3850IUF#PBF
LTC3850IUFD#PBF
LTC3850IUF#TRPBF
LTC3850IUFD#TRPBF
3850
3850
28-Lead (4mm × 4mm) Plastic QFN
28-Lead (4mm × 5mm) Plastic QFN
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
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LTC3850/LTC3850-1
E LECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 15V, VRUN1,2 = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX
Main Control Loops
VFB1,2
IFB1,2
VREFLNREG
VLOADREG
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
gm1,2
IQ
UVLO
UVLOHYS
DFMAX
VOVL
ISENSE
ITK/SS1,2
VRUN1,2
VRUN1,2HYS
VSENSE(MAX)
Transconductance Amplifier gm
Input DC Supply Current
Normal Mode
Shutdown
Undervoltage Lockout on INTVCC
UVLO Hysteresis
Maximum Duty Factor
Feedback Overvoltage Lockout
Sense Pin Bias Current
Soft-Start Charge Current
RUN Pin ON Threshold
RUN Pin ON Hysteresis
Maximum Current Sense Threshold
(Note 8)
TG RUP
TG Driver Pull-Up On-Resistance
TG RDOWN
TG Driver Pulldown On-Resistance
BG RUP
BG Driver Pull-Up On-Resistance
BG RDOWN
BG Driver Pulldown On-Resistance
TG1,2
TG1,2
ttrf
BG1,2 tr
BG1,2 tf
TG/BG t1D
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
BG/TG t2D
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
tON(MIN)
Minimum On-Time
INTVCC Linear Regulator
VINTVCC
Internal VCC Voltage
VLDO INT
INTVCC Load Regulation
VEXTVCC
EXTVCC Switchover Voltage
VLDO EXT
EXTVCC Voltage Drop
VLDOHYS
EXTVCC Hysteresis
ITH1,2 Voltage = 1.2V; (Note 4)
(Note 4)
VIN = 6V to 24V (Note 4)
(Note 4)
Measured
Measured
in
in
Servo
Servo
Loop;
Loop;
DDIITTHH
Voltage
Voltage
=
=
1.2V
1.2V
to
to
0.7V
1.6V
ITH1,2 = 1.2V; Sink/Source 5µA; (Note 4)
(Note 5)
VIN = 15V; EXTVCC Tied to VOUT1; VOUT1 = 5V
VRUN1,2 = 0V
VINTVCC Ramping Down
l
l
l
In Dropout
Measured at VFB1,2
(Each Channel) VSENSE1,2 = 3.3V
VTK/SS1,2 = 0V
VRUN1, VRUN2 Rising
l
l
VFB1,2 = 0.7V, VSENSE1,2 = 3.3V, ILIM = 0V
VFB1,2 = 0.7V, VSENSE1,2 = 3.3V, ILIM = Float
VFB1,2 = 0.7V, VSENSE1,2 = 3.3V, ILIM = INTVCC
TG High
TG Low
BG High
BG Low
(Note 6)
CCLLOOAADD
=
=
3300pF
3300pF
(Note 6)
CLOAD = 3300pF
CLOAD = 3300pF
CLOAD = 3300pF Each Driver
CLOAD = 3300pF Each Driver
(Note 7)
l
l
l
7V < VIN < 24V
ICC = 0mA to 50mA
EXTVCC Ramping Positive
ICC = 20mA, VEXTVCC = 5V
l
0.792
96
0.84
0.9
1.1
20
40
60
4.8
4.5
0.800
–10
0.002
0.01
–0.01
2.2
850
30
3
0.5
97.2
0.86
±1
1.3
1.22
80
30
50
75
2.6
1.5
2.4
1.1
25
25
25
25
30
30
90
5
0.5
4.7
50
200
0.808
–50
0.02
0.1
–0.1
50
0.88
±2
1.7
1.35
40
60
90
5.2
2
100
UNITS
V
nA
%/V
%
%
mmho
µA
µA
V
V
%
V
µA
µA
V
mV
mV
mV
mV
Ω
Ω
Ω
Ω
ns
ns
ns
ns
ns
ns
ns
V
%
V
mV
mV
38501fc
4



LT3850-1 datasheet pdf
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LT3850-1 2-Phase Synchronous Step-Down Switching Controller LT3850-1
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