LTC3786 LINER [Linear Technology], LTC3786 Datasheet

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LTC3786

Manufacturer Part Number
LTC3786
Description
Multi-Phase Current Mode Step-Up DC/DC Controller
Manufacturer
LINER [Linear Technology]
Datasheet
FeaTures
Wide V
Range: 5.5V to 36V Operation
n
IN
2-Phase Operation Reduces Input and Output
n
Capacitance
Fixed Frequency, Peak Current Mode Control
n
Internal 10V LDO Regulator
n
Lower UVLO Thresholds Allows the Use of
n
MOSFETs Rated at 6V V
GS
Adjustable Slope Compensation Gain
n
Adjustable Max Duty Cycle (Up to 96%)
n
Adjustable Leading Edge Blanking
n
±1% Internal Voltage Reference
n
Programmable Operating Frequency with One
n
External Resistor (75kHz to 500kHz)
Phase-Lockable Fixed Frequency 50kHz to 650kHz
n
SYNC Input and CLKOUT for 2-, 3-, 4-, 6- or
n
12-Phase Operation (PHASEMODE Programmable)
24-Lead Narrow SSOP Package
n
5mm × 5mm QFN Package with 0.65mm Lead Pitch
n
24-Lead Thermally Enhanced TSSOP Package
n
applicaTions
Automotive, Telecom and Industrial Power Supplies
n
Typical applicaTion
100k
24.9k
V
RUN
INTV
CC
4.7µF
LTC3862-2
BLANK
110k
FREQ
SYNC
PLLFLTR
0.1µF
SS
1nF
3V8
FB
10nF
ITH
PHASEMODE
SGND
12.1k
796k
12.4k
220pF
Multi-Phase Current Mode
Step-Up DC/DC Controller
DescripTion
The LTC
3862-2 is a two-phase constant frequency, current
®
mode boost and SEPIC controller that drives N-channel
power MOSFETs. Two-phase operation reduces system
filtering capacitance and inductance requirements.
The operating frequency can be set with an external resistor
over a 75kHz to 500kHz range and can be synchronized
to an external clock using the internal PLL. Multiphase
operation is possible using the SYNC input, the CLKOUT
output and the PHASEMODE control pin allowing 2-, 3-,
4-, 6- or 12-phase operation.
Other features include an internal 10V LDO with under-
voltage lockout protection for the gate drivers, a preci-
sion RUN pin threshold with programmable hysteresis,
soft-start and programmable leading edge blanking and
maximum duty cycle.
PART NUMBER
LTC3862
LTC3862-1
LTC3862-2
L, LT, LTC, LTM, Linear Technology, the Linear logo and PolyPhase are registered trademarks
and No R
SENSE
trademarks are the property of their respective owners. Protected by U.S. Patents, including
6144194, 6498466, 6611131.
V
IN
6V TO 32V
22µF
16µH
16µH
50V
V
OUT
80V
IN
7A (MAX)
GATE1
+
SENSE1
210µF
0.0033
100V
SENSE1
GATE2
+
SENSE2
0.0033
SENSE2
PGND
CLKOUT
SLOPE
D
MAX
38622 TA01a
LTC3862-2
+
INTV
UV
CC
5V
3.3V
10V
7.5V
10V
4.4V
and ThinSOT are trademarks of Linear Technology Corporation. All other
Efficiency vs Output Current
97
V
= 80V
OUT
95
93
91
89
87
85
83
81
79
77
10
100
1000
LOAD CURRENT (mA)
UV
2.9V
7.0V
3.9V
V
= 6V
IN
V
= 9V
IN
V
= 12V
IN
V
= 24V
IN
10000
38622 TA01b
38622f
1

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LTC3786 Summary of contents

Page 1

FeaTures Wide V Range: 5.5V to 36V Operation n IN 2-Phase Operation Reduces Input and Output n Capacitance Fixed Frequency, Peak Current Mode Control n Internal 10V LDO Regulator n Lower UVLO Thresholds Allows the Use of n MOSFETs Rated ...

Page 2

LTC3862-2 absoluTe MaxiMuM raTings Input Supply Voltage (V ) ......................... –0.3V to 40V IN INTV Voltage ..........................................–0.3V to 11V CC INTV LDO RMS Output Current .........................50mA CC RUN Voltage................................................. –0. SYNC Voltage ............................................... –0. SLOPE, PHASEMODE, ...

Page 3

LEAD FREE FINISH TAPE AND REEL LTC3862EFE-2#PBF LTC3862EFE-2#TRPBF LTC3862IFE-2#PBF LTC3862IFE-2#TRPBF LTC3862HFE-2#PBF LTC3862HFE-2#TRPBF LTC3862EGN-2#PBF LTC3862EGN-2#TRPBF LTC3862IGN-2#PBF LTC3862IGN-2#TRPBF LTC3862HGN-2#PBF LTC3862HGN-2#TRPBF LTC3862EUH-2#PBF LTC3862EUH-2#TRPBF LTC3862IUH-2#PBF LTC3862IUH-2#TRPBF LTC3862HUH-2#PBF LTC3862HUH-2#TRPBF Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade ...

Page 4

LTC3862-2 elecTrical characTerisTics specified operating junction temperature range, otherwise specifications are at T otherwise noted. SYMBOL PARAMETER V Error Amplifier Maximum Output Voltage ITH (Internally Clamped) Error Amplifier Minimum Output Voltage I Error Amplifier Output Source Current ITH Error Amplifier ...

Page 5

T otherwise noted. SYMBOL PARAMETER t Minimum On-Time ON(MIN)1 t Minimum On-Time ON(MIN)2 t Minimum On-Time ON(MIN)3 Gate Driver R Driver Pull-Up R DS(ON) DS(ON) Driver Pull-Down R DS(ON) ...

Page 6

LTC3862-2 Typical perForMance characTerisTics Efficiency vs Output Current 80V OUT 12V 24V ...

Page 7

Typical perForMance characTerisTics INTV vs Temperature CC 10.05 10.04 10.03 10.02 10.01 10.00 9.99 9.98 9.97 9.96 9.95 – –25 0 100 125 TEMPERATURE (°C) 38622 G10 Feedback Voltage vs Temperature 1.235 1.233 1.231 1.229 1.227 1.225 ...

Page 8

LTC3862-2 Typical perForMance characTerisTics RUN Threshold vs Input Voltage 1.5 1.4 1.3 ON 1.2 OFF 1.1 1 INPUT VOLTAGE (V) 38622 G19 RUN Source Current vs Input Voltage 0 –1 –2 –3 ...

Page 9

Typical perForMance characTerisTics Frequency vs PLLFLTR Voltage 1400 1200 1000 800 600 400 200 0 0 PLLFLTR VOLTAGE (V) 38622 G28 Minimum On-Time vs Input Voltage 430 380 BLANK = 3V8 330 BLANK = FLOAT 280 ...

Page 10

LTC3862-2 pin FuncTions 3V8: Output of the Internal 3.8V LDO from INTV pin for the low voltage analog and digital circuits. A low ESR 1nF ceramic bypass capacitor should be connected between 3V8 and SGND, as close as possible to ...

Page 11

FuncTions + + SENSE1 , SENSE2 : Positive Inputs to the Current Comparators. The ITH pin voltage programs the current comparator offset in order to set the peak current trip threshold. This pin is normally connected to a sense ...

Page 12

LTC3862-2 FuncTional DiagraM CLKOUT SYNC PLLFLTR MAX PHASEMODE FREQ R FREQ SLOPE SLOPE COMPENSATION BLANK BLANK BLOGIC LOGIC 3V8 5µ ITH PSKIP PSKIP + – ...

Page 13

The Control Loop The LTC3862-2 uses a constant frequency, peak current mode step-up architecture with its two channels operat- ing 180 degrees out-of-phase. During normal operation, each external MOSFET is turned on when the clock for that channel sets ...

Page 14

LTC3862-2 operaTion In multi-phase applications, all of the FB pins are connected together and all of the error amplifier output pins (ITH) are connected together. The INTV pins, however, should not CC be connected together. The INTV CC sourcing current ...

Page 15

To prevent the maximum junction temperature from be- ing exceeded, the input supply current to the IC should be checked when operating in continuous mode (heavy load) at maximum trade-off between the operat- IN ing frequency ...

Page 16

LTC3862-2 operaTion Operation at High Supply Voltage At high input voltages, the LTC3862-2’s internal LDO can dissipate a significant amount of power, which could cause the maximum junction temperature to be exceeded. Conditions such as a high operating frequency, or ...

Page 17

Operation of the RUN Pin The control circuitry in the LTC3862-2 is turned on and off using the RUN pin. Pulling the RUN pin below 1.22V forces shutdown mode and releasing it allows a 0.5μA current source to pull ...

Page 18

LTC3862-2 operaTion The LTC3862-2 uses a constant frequency architecture that can be programmed over a 75kHz to 500kHz range using a single resistor from the FREQ pin to ground. Figure 6 illustrates the relationship between the FREQ pin resistance and ...

Page 19

Using the LTC3862-2 Transconductance (g Amplifier in Multi-Phase Applications The LTC3862-2 error amplifier is a transconductance amplifier, meaning that it has high DC gain but high output impedance (the output of the error amplifier is a current ...

Page 20

LTC3862-2 operaTion one LTC3862-2 chip, connect all of the SS pins together and use one external capacitor to program the soft-start time. In this case, the current into the soft-start capaci- tor will • 5μA, where ...

Page 21

When excess slope compensation is applied to the internal current sense signal, the phase margin of the control loop suffers. Figure ...

Page 22

LTC3862-2 operaTion MINIMUM ON-TIME AT LIGHT LOAD WITH BLANK = SGND INDUCTOR CURRENT 200mA/DIV GATE 5V/DIV SW NODE 20V/DIV V = 36V 500ns/DIV 72V OUT MEASURED ON-TIME = 210ns MINIMUM ON-TIME AT LIGHT LOAD WITH BLANK = ...

Page 23

The SENSE and SENSE Pins + – The SENSE and SENSE pins are high impedance inputs to the CMOS current comparators for each channel. Nominally, there current into or out of these pins. There ...

Page 24

LTC3862-2 operaTion The ITH series R • C filter sets the dominant pole-zero C C loop compensation. The transfer function for boost and flyback converters contains a right half plane zero that normally requires the loop crossover frequency to be ...

Page 25

Typical Boost Applications Circuit A basic 2-phase, single output LTC3862-2 application circuit is shown in Figure 18. External component selec- tion is driven by the characteristics of the load and the input supply. Duty Cycle Considerations For a ...

Page 26

LTC3862-2 applicaTions inForMaTion Maximum Duty Cycle Limitations Another operating extreme occurs at high duty cycle, when the input voltage is low and the output voltage is high. In this case – V   IN(MIN) ...

Page 27

The inductor saturation current rating needs to be higher than the worst-case peak inductor current during an overload condition the maximum rated load O(MAX) current, then the maximum current limit value (I would normally be ...

Page 28

LTC3862-2 applicaTions inForMaTion The power dissipated by the MOSFET in a multi-phase boost converter with n phases is: 2  I  O(MAX • R   FET DS(ON) n • 1– D   MAX ...

Page 29

For a boost converter where the current limit value is chosen to be 30% higher than the maximum load current, the peak current in the MOSFET and sense resistor is: χ 1  • ...

Page 30

LTC3862-2 applicaTions inForMaTion power dissipation is important when deciding on a diode current rating, package type, and method of heat sinking close approximation, the power dissipated by the diode is • V • (1 – ...

Page 31

For the bulk capacitance, which we assume contributes 1% to the total output ripple, the minimum required ca- pacitance is approximately: I O(MAX) ≥ C OUT 0.01• n • V • f OUT For many designs it will ...

Page 32

LTC3862-2 applicaTions inForMaTion The value of the input capacitor is a function of the source impedance, and in general, the higher the source impedance, the higher the required input capacitance. The required amount of input capacitance is also greatly affected ...

Page 33

D MAX SLOPE BLANK PHASEMODE 45.3k FREQ 0.1µF SS LTC3862-2 1.5nF 45.3k ITH 100pF FB 5.62k SGND 324k V OUT CLKOUT SYNC PLLFLTR Figure 25a. A 8.5V to 36V Input, 72V/2A Output 2-Phase Boost Converter Application Circuit 2.5 ...

Page 34

LTC3862-2 applicaTions inForMaTion The inductor value chosen was 57.8μH and the part number is PA2050-583, manufactured by Pulse Engi- neering. This inductor has a saturation current rating of 5A. 8. The power MOSFET chosen for this application is a Renesas ...

Page 35

For the bulk capacitance, which we assume contributes 1% to the total output ripple, the minimum required capacitance is approximately: I O(MAX) C ≥ = OUT 0.01• n • V • f 0.01• 2 • 72V • 300kHz ...

Page 36

LTC3862-2 applicaTions inForMaTion 10. The output resistor divider should be located as close as possible to the IC, with the bottom resistor connected between FB and SGND. The PCB trace connecting the top resistor to the upper terminal of the ...

Page 37

Typical applicaTions 60V Input, 12V/6A Output 2-Phase SEPIC Application Circuit Q3 PBSS9110T PBZ6.8B 220k 10k R12 56k R27 Q2 22k PMST5550 R13 Q5 10k PMST5550 D MAX SLOPE 3V8 BLANK PHASEMODE R C OSC ...

Page 38

LTC3862-2 Typical applicaTions 32V Input, 80V/7A Output 2-Phase Boost Converter Application Circuit D MAX SLOPE BLANK PHASEMODE 110k FREQ 0.1µF SS 10nF LTC3862-2 12k ITH 220pF FB 12.4k SGND 796k V OUT CLKOUT SYNC PLLFLTR Start-Up RUN ...

Page 39

Typical applicaTions A 24V Input, 48V/6A Output 2-Phase Boost Converter Application Circuit D MAX SLOPE BLANK PHASEMODE 45.3k FREQ 0.1µF SS 4.7nF LTC3862-2 30.1k ITH 100pF FB 7.87k SGND 301k V OUT CLKOUT SYNC PLLFLTR Start-Up RUN 5V/DIV I L1 ...

Page 40

LTC3862-2 Typical applicaTions A 24V Input, 107V/1.5A Output 2-Phase Boost Converter Application Circuit D MAX SLOPE BLANK PHASEMODE 68.1k FREQ 0.1µF SS 2200pF LTC3862-2 43.5k ITH 47pF FB 6.65k SGND 576k V OUT CLKOUT SYNC PLLFLTR L1, L2: CHAMPS TECHNOLOGIES ...

Page 41

DescripTion Please refer to http://www.linear.com/designtools/packaging/ 6.60 ±0.10 4.50 ±0.10 SEE NOTE 4 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 0.50 – 0.75 (.0035 – .0079) (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS ...

Page 42

LTC3862-2 package DescripTion Please refer to http://www.linear.com/designtools/packaging/ .254 MIN .0165 ±.0015 RECOMMENDED SOLDER PAD LAYOUT .0075 – .0098 (0.19 – 0.25) .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING ...

Page 43

DescripTion Please refer to http://www.linear.com/designtools/packaging/ 5.40 ±0.05 3.90 ±0.05 3.20 ± 0.05 3.25 REF 3.20 ± 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 ± 0.10 PIN 1 TOP MARK (NOTE 6) ...

Page 44

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