LTC3731H Linear Technology, LTC3731H Datasheet

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LTC3731H

Manufacturer Part Number
LTC3731H
Description
Synchronous Buck Switching Regulator Controller
Manufacturer
Linear Technology
Datasheet

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APPLICATIO S
FEATURES
TYPICAL APPLICATIO
3-Phase Current Mode Controller with Onboard
MOSFET Drivers
±5% Output Current Matching Optimizes Thermal
Performance and Size of Inductors and MOSFETs
±2% V
Reduced Power Supply Induced Noise
±10% Power Good Output Indicator
250kHz to 600kHz Per Phase, PLL, Fixed Frequency
PWM, Stage Shedding
OPTI-LOOP
Adjustable Soft-Start Current Ramping
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Soft Latch
Adjustable Undervoltage Lockout Threshold
Selectable Phase Output for Up to 12-Phase Operation
Available in 36-Pin Narrow (0.209") SSOP Package
Automotive and Industrial Power Supplies
High Output Current DC/DC Power Supplies
REF
Accuracy Over Temperature up to 140°C
®
Compensation Minimizes C
U
4.5V TO 7V
POWER GOOD INDICATOR
V
IN
TM
V
CC
OPTIONAL SYNC IN
or Burst Mode
36k
12k
5k
6.04k
10µF
0.1µF
Figure 1. High Current Triple Phase Step-Down Converter
U
7.5k
SW3 SW2 SW1
680pF
100pF
0.01µF
®
OUT
Operation
V
BOOST1
BOOST2
BOOST3
PGOOD
PLLIN
PLLFLTR
UVADJ
I
RUN/SS
SGND
EAIN
TH
CC
LTC3731H
SENSE1
SENSE1
SENSE2
SENSE2
SENSE3
SENSE3
PGND
SW1
SW2
SW3
BG1
BG2
BG3
Synchronous Buck Switching
TG1
TG2
TG3
+
+
+
DESCRIPTIO
The LTC
switching regulator controller that drives all N-channel
external power MOSFET stages in a phase-lockable fixed
frequency architecture. The LTC3731H is rated for opera-
tion up to 140°C junction temperature. The 3-phase con-
troller drives its output stages with 120° phase separation
at frequencies up to 600kHz per phase to minimize the
RMS current losses in both the input and output filter
capacitors. The 3-phase technique effectively triples the
fundamental frequency, improving transient response while
operating each controller at an optimal frequency for
efficiency and ease of thermal design. Light load efficiency
is optimized by using a choice of output Stage Shedding
or Burst Mode operation.
The precision reference supports output voltages from 0.6V
to 6V. Current foldback provides protection for the exter-
nal MOSFETs under short-circuit or overload conditions.
Please refer to the LTC3731 data sheet for 0°C to 70°C and
–40°C to 85°C rated versions.
Burst Mode, OPTI-LOOP and PolyPhase are registered trademarks of Linear Technology
Corporation. Stage Shedding is a trademark of Linear Technology Corporation.
Protected by U.S. Patents including 5481178, 5929620, 6177787, 6144194, 6100678,
5408150, 6580258, 6462525, 6304066, 5705919.
All other trademarks are the property of their respective owners.
, LTC and LT are registered trademarks of Linear Technology Corporation.
V
V
IN
IN
0.8µH
0.8µH
0.8µH
®
3731H is a PolyPhase
0.003Ω
0.003Ω
0.003Ω
Regulator Controller
U
+
3-Phase, 600kHz,
+
3731H F01
C
470µF
4V
22µF
35V
V
1.35V
55A
OUT
OUT
V
5V TO 28V
IN
®
synchronous step-down
LTC3731H
3731hf
1

Related parts for LTC3731H

LTC3731H Summary of contents

Page 1

... The LTC switching regulator controller that drives all N-channel external power MOSFET stages in a phase-lockable fixed frequency architecture. The LTC3731H is rated for opera- tion up to 140°C junction temperature. The 3-phase con- troller drives its output stages with 120° phase separation ...

Page 2

... MIN TYP 0.594 0.600 ● 0.590 0.600 65 75 ● – = 0.6V, 1. –5 ● Voltage = 1.2V to 0.7V 0.1 TH ● Voltage = 1. –0.1 TH 0.03 ● ● 0.54 0. ORDER PART NUMBER LTC3731HG MAX UNITS 0.606 V 0.614 0.7 % –0.7 % %/V 7 mmho MHz 0.66 V 3731hf ...

Page 3

... Tested with a Square Wave (Note 2mA PGOOD PGOOD V with Respect to Set Output Voltage, EAIN PGOOD Goes Low After V Delay UVDLY After V is Forced Outside the PGOOD Thresholds EAIN V = 1.2V PLLFLTR PLLFLTR V = 2.4V PLLFLTR LTC3731H MIN TYP MAX UNITS µA 0.2 0.7 V – 1.5 V – 0.7 V – 0 3.3 3.8 4.5 1.13 1.18 1.23 0 2.3 3 ...

Page 4

... CLKOUT Controller CLKOUT Phase Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3731H is guaranteed to meet specifications from –40°C to 140°C. Junction temperature ( calculated from the ambient J temperature T and power dissipation P ...

Page 5

... TEMPERATURE (°C) 3731H G05 Undervoltage Reset Voltage vs Temperature PLLFLTR –50 – 1.5 2 2.5 TEMPERATURE (°C) 3731H G08 LTC3731H I = 20A LOAD V = 1.5V OUT 400 500 600 3731H G03 Threshold 0. 100 125 150 3731H G06 50 ...

Page 6

... LTC3731H TYPICAL PERFOR A CE CHARACTERISTICS Short-Circuit Arming and Latchoff vs Temperature 5 ARMING 4 LATCHOFF 3 2 www.DataSheet4U.com 1 0 –50 – TEMPERATURE (°C) Maximum SENSE RUN/ VOLTAGE (V) RUN/SS Percentage of Nominal Output vs Peak I (Foldback) SENSE 80 70 ...

Page 7

... V SW3 10V/DIV V = 12V 4µs/DIV 1.5V OUT FCB FREQUENCY = 225kHz W U AC, 20mV/DIV 3731H G20 AC, 20mV/DIV 3731H G22 LTC3731H Burst Mode at 1 Amp, Light Load Current (Circuit of Figure 14) V OUT V SW1 10V/DIV V SW2 10V/DIV V SW3 10V/DIV V = 12V 4µs/DIV 1.5V OUT ...

Page 8

... LTC3731H CTIO S BG1 to BG3: High Current Gate Drives for Bottom N-Channel MOSFETs. Voltage swing at these pins is from ground to V BOOST1 to BOOST3: Positive Supply Pins to the Topside Floating Drivers. Bootstrapped capacitors, charged with exter- nal Schottky diodes and a boost voltage source, are connected between the BOOST and SW pins ...

Page 9

... 3mV SLOPE COMP 5 0.86V 54k SS CLAMP 2.4V FCB SHED V CC SHDN RUN 1.5µA RST SOFT- 5(V ) START FB 6V Figure 2 LTC3731H BOOST BOT TOP FORCE BOT SW SWITCH LOGIC V (VDR BOT FCB PGND SHDN – – SENSE ...

Page 10

... LTC3731H U OPERATIO (Refer to Functional Diagram) Main Control Loop The IC uses a constant frequency, current mode step- down architecture. During normal operation, each top MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the main current comparator resets each RS latch. The peak inductor ...

Page 11

... Foldback current limit can be overrid- den by clamping the EAIN pin such that the voltage is held above the (70%)(0.6V) or 0.42V level even when the actual output voltage is low 100µA of input current can safely be accommodated by the RUN/SS pin. LTC3731H will result 3731hf 11 ...

Page 12

... LTC3731H U OPERATIO (Refer to Functional Diagram) Input Undervoltage Reset The RUN/SS capacitor will be reset if the input voltage allowed to fall below approximately 4V. The CC capacitor on the RUN/SS pin will be discharged until the short-circuit arming latch is disarmed. The RUN/SS ca- pacitor will attempt to cycle through a normal soft-start www ...

Page 13

... MOSFETs selected take into account the voltage step-down ratio as well as the actual position (main or synchronous) in which the MOS- FET will be used. A much smaller and much lower input capacitance MOSFET should be used for the top MOSFET LTC3731H 1.0 1-PHASE 0.9 2-PHASE 3-PHASE 0 ...

Page 14

... LTC3731H U U APPLICATIO S I FOR ATIO in applications that have an output voltage that is less than 1/3 of the input voltage. In applications where V the top MOSFETs’ “on” resistance is normally less impor- tant for overall efficiency than its input capacitance at operating frequencies above 300kHz. MOSFET manufac- turers have designed special purpose devices that provide reasonably low “ ...

Page 15

... The Figure 6 graph shows that the peak RMS input current is reduced linearly, inversely proportional to the number N of stages used important to note that the efficiency loss is proportional to the input RMS current squared and therefore a 3-stage implementation results in 90% less /V . OUT IN LTC3731H V k OUT = = 1 2 where ..., – N ...

Page 16

... LTC3731H U U APPLICATIO S I FOR ATIO power loss when compared to a single phase design. Battery/input protection fuse resistance (if used), PC board trace and connector resistance losses are also reduced by the reduction of the input ripple current in a PolyPhase system. The required amount of input capaci- tance is further reduced by the factor, N, due to the effective increase in the frequency of the current pulses ...

Page 17

... RUN/SS pin even though the voltage at the pin may exceed the absolute maximum rating for the pin. This is a result of the limited current and the internal protection circuit on the pin. The following explanation describes how this function operates. LTC3731H , connected to the BOOST ...

Page 18

... LTC3731H U U APPLICATIO S I FOR ATIO An internal 1.5µA current source charges up the C capacitor. When the voltage on RUN/SS reaches 1.5V, the controller is permitted to start operating. As the voltage on RUN/SS increases from 1.5V to 3.5V, the internal current limit is increased from 20mV/R The output current limit ramps up slowly, taking an additional 1s/µ ...

Page 19

... CALCULATE FOR 0.42V TO 0.55V Figure 8. Foldback Current Elimination LTC3731H . A voltage applied ∆f = ±0 greater than the oscil- PLLIN , current is sourced continuously, OSC , current is sunk continuously, pulling OSC V CC LTC3731H EAIN 3731H F08 , is H 3731hf 19 ...

Page 20

... LTC3731H U U APPLICATIO S I FOR ATIO www.DataSheet4U.com down the PLLFLTR pin. If the external and internal fre- quencies are the same, but exhibit a phase difference, the current sources turn on for an amount of time correspond- ing to the phase difference. Thus, the voltage on the PLLFLTR pin is adjusted until the phase and frequency of the external and internal oscillators are identical ...

Page 21

... If C than that the load rise time is limited to approximately external com- TH 1000 • SENSE the charging current to about 1A. LTC3731H pin waveforms TH pin signal which is in the TH and the bandwidth of the loop will increased by the same ...

Page 22

... Although the IC has a maximum input voltage of 32V on the SW pins, most applications will be limited to 30V by the MOSFET LTC3731H Figure 10. Automotive Application Protection Design Example As a design example, assume The inductance value is chosen first based upon a 30% ripple current assumption ...

Page 23

... IC and especially the “quiet” side of the IC. Separate the high dv/dt traces from sensitive small-signal nodes with ground traces or ground planes. 6) Use a low impedance source such as a logic gate to drive the PLLIN pin and keep the lead as short as possible. LTC3731H and C . The V decoupling capacitor should be IN ...

Page 24

... LTC3731H U U APPLICATIO S I FOR ATIO www.DataSheet4U.com BOLD LINES INDICATE HIGH, SWITCHING CURRENT LINES. KEEP LINES TO A MINIMUM LENGTH LTC3731H + SENSE – SENSE Figure 12. Kelvin Sensing SW1 D1 L2 SW2 D2 L3 SW3 D3 Figure 11. Branch Current Waveforms INDUCTOR ...

Page 25

... Figure 13 graphically illustrates the principle. SINGLE PHASE CIN I COUT TRIPLE PHASE V SW1 V SW2 V SW3 CIN I COUT 3731H F13 Figure 13. Single and Polyphase Current Waveforms LTC3731H 3731hf 25 ...

Page 26

... LTC3731H U U APPLICATIO S I FOR ATIO The worst-case input RMS ripple current for a single stage design peaks at twice the value of the output voltage. The worst-case input RMS ripple current for a two stage design results in peaks at 1/4 and 3/4 of the input voltage, and the worst-case input RMS ripple current for a three stage design results in peaks at 1/6, 1/2, and 5/6 of the input voltage ...

Page 27

... DC loss. A smaller, less expensive MOSFET can actually perform better in the task of the main switch. V DSSPEC LTC3731H = 8V, 0.12W 20V. The bottom MOSFET does not IN 2 • 3(0.7V)(15A)(50ns)(4E5) Main switch’s AC loss (V = 12V) 2.25W 3.75% IN Main switch’s DC loss Synchronous switch AC loss ...

Page 28

... SWITCHING FREQUENCY: 300kHz 10Ω CLK PLLIN PGOOD 3 34 PLLFLTR BOOST1 1Ω 0.1µ FCB TG1 SW1 LTC3731H BOOST2 0.1µ TG2 8 29 EAIN SW2 9 28 SGND SENSE1 BG1 1µF 10µ – ...

Page 29

... M16 L6 0.002Ω 0.1µ M17, L6: TOKO FDH1040: 0.56µH : 10µF/16V CERAMIC × 270µF/16V SANYO Os-Con 100µF/6.3V/X5R × 330µF/4V × OUT LTC3731H V5 + 10µF Cer. 10V – S1 – S2 – OUT + C OUT ...

Page 30

... CLK PLLIN PGOOD PLLFLTR BOOST1 Si7852DP 4 33 FCB TG1 5 32 R23 NC SW1 0.007Ω BOOST2 TG2 LTC3731H 8 29 EAIN SW2 9 28 SGND SENSE1 BG1 4.7µ – SENSE1 PGND SENSE2 BG2 13 24 – SENSE2 ...

Page 31

... Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC3731H 12.50 – 13.10* (.492 – .516) 35 ...

Page 32

... LTC3731H RELATED PARTS PART NUMBER DESCRIPTION LTC1628/LTC3728 2-Phase, Dual Output Synchronous Step-Down DC/DC Controllers LTC1629/LTC3729 20A to 200A PolyPhase Synchronous Controllers LTC1702 No R SENSE Controller LTC1703 No R SENSE Controller with 5-Bit Mobile VID Control LTC1708-PG 2-Phase, Dual Synchronous Controller with Mobile VID www.DataSheet4U.com ® ...

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