Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage regulators - DC DC switch controllers TSSOP 38 EP

LT3791-1

37911f

Typical applicaTion

FeaTures DescripTion

60V 4-Switch Synchronous

Buck-Boost Controller

The LT

3791-1 is a synchronous 4-switch buck-boost volt-

age/current regulator controller. The controller can regulate

output voltage, output current, or input current with input

voltages above, below, or equal to the output voltage. The

constant-frequency, current mode architecture allows its

frequency to be adjusted or synchronized from 200kHz

to 700kHz. No top FET refresh switching cycle is needed

in buck or boost operation. With 60V input, 60V output

capability and seamless transitions between operating

regions, the LT3791-1 is ideal for voltage regulator, bat-

tery/super-capacitor charger applications in automotive,

industrial, telecom, and even battery-powered systems.

The LT3791-1 provides input current monitor, output

current monitor, and various status flags, such as C/10

charge termination and shorted output flag.

L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

120W (24V 5A) Buck-Boost Voltage Regulator

applicaTions

4-Switch Single Inductor Architecture Allows V

Above, Below or Equal to V

OUT

Synchronous Switching: Up to 98.5% Efficiency

Wide V

Range: 4.7V to 60V

2% Output Voltage Accuracy: 1.2V ≤ V

OUT

< 60V

6% Output Current Accuracy: 0V ≤ V

OUT

< 60V

Input and Output Current Regulation with Current

Monitor Outputs

No Top FET Refresh in Buck or Boost

OUT

Disconnected from V

During Shutdown

C/10 Charge Termination and Output Shorted Flags

Capable of 100W or greater per IC

38-Lead TSSOP with Exposed Pad

Efficiency vs Load Current

Automotive, Telecom, Industrial Systems

High Power Battery-Powered System

LOAD CURRENT (A)

0 1

EFFICIENCY (%)

100

37911 TA01b

2 3 4

= 12V

= 24V

= 54V

12V TO

58V

INTV

TG1

BG1

SNSP

SNSN

BST1

BST2

BG2

PGND

SW2

TG2

LT3791-1

SWI

SHORT

C/10

CCM

470nF

IVINN

IVINP

IVINMON

ISMON

CLKOUT

PWMOUT

TEST1

EN/UVLO

OVLO

REF

PWM

CTRL

147k

200kHz

SYNCSS SGND

1µF

499k

56.2k

100k

499k

27.4k

INTV

0.1µF

33nF

10nF

37911 TA01a

0.004Ω

ISP

ISN

0.1µF

10µH

0.1µF

4.7µF

50V

×2

4.7µF

100V

47µF

80V

0.015Ω

OUT

24V

73.2k

3.83k

5.1k

220µF

35V

100k 200k

0.003Ω

50Ω

Summary of content (24 pages)

PAGE 1
LT3791-1 60V 4-Switch Synchronous Buck-Boost Controller Features n n n n n n n n n n n Description 4-Switch Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT Synchronous Switching: Up to 98.5% Efficiency Wide VIN Range: 4.7V to 60V 2% Output Voltage Accuracy: 1.
PAGE 2
LT3791-1 Absolute Maximum Ratings (Note 1) Pin Configuration Supply Voltages Input Supply (VIN)......................................................60V SW1, SW2.......................................................–1V to 60V C/10, SHORT..............................................................15V EN/UVLO, IVINP, IVINN, ISP, ISN...............................60V INTVCC, (BST1-SW1), (BST2-SW2)..............................6V CCM, SYNC, RT, CTRL, OVLO, PWM...........................
PAGE 3
LT3791-1 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, VEN/UVLO = 12V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX 1.16 1.2 1.24 UNITS Logic Inputs EN/UVLO Falling Threshold l EN/UVLO Rising Hysteresis 15 EN/UVLO Input Low Voltage IVIN Drops Below 1µA EN/UVLO Pin Bias Current Low VEN/UVLO = 1V EN/UVLO Pin Bias Current High VEN/UVLO = 1.
PAGE 4
LT3791-1 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, VEN/UVLO = 12V unless otherwise noted. PARAMETER CONDITIONS C/10 Rising Threshold (VFB) V(ISP-ISN) = 0V C/10 Falling Threshold (VFB) C/10 Falling Threshold (V(ISP-ISN)) VFB = 1.2V MIN TYP MAX UNITS l 1.127 1.15 1.173 V l 1.078 1.1 1.
PAGE 5
LT3791-1 Typical Performance Characteristics INTVCC Dropout Voltage vs Current, Temperature 80 5.15 5.10 1.5 INTVCC (V) VIN-VINTVCC (V) 90 5.20 TA = 150°C TA = 25°C TA = –50°C 2.0 INTVCC Current Limit vs Temperature INTVCC Voltage vs Temperature INTVCC CURRENT LIMIT (mA) 2.5 TA = 25°C, unless otherwise noted. 1.0 5.05 VIN = 60V 5.00 VIN = 12V 4.95 4.90 0.5 4.
PAGE 6
LT3791-1 Typical Performance Characteristics 120 V(ISP-ISN) Threshold vs VFB TA = 25°C, unless otherwise noted. ISMON Voltage vs Temperature 1.04 VIN = 12V V(ISP-ISN) = 100mV 1.03 100 1.0 0.9 0.8 60 40 0.7 1.01 VISMON (V) VISMON (V) V(ISP-ISN) (mV) 1.02 80 1.00 0.99 1.19 1.18 1.20 1.21 VFB (V) 1.22 0 25 50 75 100 125 150 TEMPERATURE (°C) V(IVINP-IVINN) Threshold vs VIVINP 1.04 54 51.5 1.03 51.0 1.02 50.5 1.01 50 VIVINP = 3V 48 46 44 42 –50 –25 0 50.0 49.5 48.5 0.
PAGE 7
LT3791-1 Typical Performance Characteristics C/10 Threshold vs Temperature OVLO Threshold vs Temperature 1.125 FALLING 1.100 1.075 1.050 1.025 1.000 –50 –25 0 16 3.2 14 3.1 12 RISING 3.0 2.9 FALLING 2.7 4 2.6 2 0 Supply Current vs Input Voltage 7 IQ (mA) 2.0 1.5 1.0 TA = 150°C TA = 25°C TA = –50°C 0 0 10 20 30 VIN (V) 40 50 60 5 4 3 2 RT = 59.0k RT = 147k 200 100 0 25 50 75 100 125 150 TEMPERATURE (°C) 37911 G25 RISING 1.20 1.18 FALLING 1.16 1.14 1.12 0 –50 –25 1.
PAGE 8
LT3791-1 Typical Performance Characteristics BG1, BG2 Driver On-Resistance vs Temperature 4.5 3.8 4.0 RISING 3.7 3.6 3.5 3.4 FALLING 3.3 3.2 4.0 3.5 PULL-UP 3.5 3.0 2.5 2.0 PULL-DOWN 1.5 1.0 0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 37911 G28 PWMOUT RESISTANCE (Ω) 14 1.6 12 1.4 1.0 25 50 75 100 125 150 TEMPERATURE (°C) V(SNSP-SNSN) Buck Threshold vs VC VC (V) 60 40 BG2 1.0 PULL-DOWN 0 37911 G30 V(SNSP-SNSN) = 0V 1.2 PULL-UP 6 1.
PAGE 9
LT3791-1 Pin Functions CTRL (Pin 1): Output Current Sense Threshold Adjustment Pin. Regulating threshold V(ISP-ISN) is 1/10th of (VCTRL – 200mV). CTRL linear range is from 200mV to 1.1V. For VCTRL > 1.3V, the current sense threshold is constant at the full-scale value of 100mV. For 1.1V < VCTRL < 1.3V, the dependence of the current sense threshold upon VCTRL transitions from a linear function to a constant value, reaching 98% of full scale by VCTRL = 1.2V.
PAGE 10
LT3791-1 Pin Functions BST2 (Pin 22): Bootstrapped Driver Supply. The BST2 pin swings from a diode voltage below INTVCC up to a diode voltage below VOUT + INTVCC. NC (Pin 23): No Connect Pin. Leave this pin floating. TG2 (Pin 24): Top Gate Drive. Drives the top N-channel MOSFET with a voltage equal to INTVCC superimposed on the switch node voltage SW2. ISP (Pin 25): Connection Point for the Positive Terminal of the Output Current Feedback Resistor.
PAGE 11
LT3791-1 Block Diagram 26 – + A = 10 7 8 9 A1 A = 10 A = 20 ISMON_INT A = 24 33 13 VREF INTVCC REGS SHDN_INT TSD IVINMON_INT BST1 + A13 A3 EN/UVLO – A4 SHDN_INT SHDN_INT SS_RESET SS LATCH PWM + INTVCC A14 BG1 A15 17 BG2 19 SLOPE_COMP_BOOST INTVCC RT BOOST LOGIC SYNC CLKOUT SW2 + A16 0.4V – + SNSP – SNSN A11 FB + C/10 + A8 A6 – Q R S VREF 0.2V 1.15V + SS LATCH 22 27 28 IVINMON_INT FB 37 1.
PAGE 12
LT3791-1 Operation The LT3791-1 is a current mode controller that provides an output voltage above, equal to or below the input voltage. The LTC proprietary topology and control architecture uses a current sensing resistor in buck or boost operation. The sensed inductor current is controlled by the voltage on the VC pin, which is the output of the feedback amplifiers A11 and A12.
PAGE 13
LT3791-1 Operation synchronous buck regulator. The duty cycle of switch M1 increases until the maximum duty cycle of the converter in buck operation reaches DMAX(BUCK, TG1), given by: M2 + M4 M2 + M4 M1 + M4 M2 + M4 M1 + M4 M1 + M4 DMAX(BUCK,TG1) = 100% – D(BUCK-BOOST) where D(BUCK-BOOST) is the duty cycle of the buck-boost switch range: 37911 F03 Figure 3. Buck Operation (VIN > VOUT) D(BUCK-BOOST) = 8% Figure 3 shows typical buck operation waveforms.
PAGE 14
LT3791-1 Applications Information The Typical Application on the front page is a basic LT3791-1 application circuit. External component selection is driven by the load requirement, and begins with the selection of RSENSE and the inductor value. Next, the power MOSFETs are selected. Finally, CIN and COUT are selected. This circuit can operate up to an input voltage of 60V.
PAGE 15
LT3791-1 Applications Information current in boost operation and the maximum inductor valley current in buck operation. In boost operation, the maximum average load current at VIN(MIN) is:  51mV ∆IL  VIN(MIN) IOUT(MAX _ BOOST) =  – •  RSENSE 2  VOUT where ΔIL is peak-to-peak inductor ripple current. In buck operation, the maximum average load current is:  47.
PAGE 16
LT3791-1 Applications Information The rising OVLO value can be accurately set by the resistor divider R3 and R4. The following equations should be used to determine the resistor values: VIN(OVLO + ) = 3 • VCTRL (V) R3+R4 R4 R3+R4 VIN(OVLO –) = 2.925 • R4 LT3791-1 V(ISP-ISN) (mV) 1.1 90 1.15 94.5 1.2 98 1.25 99.5 1.3 100 When VCTRL is higher than 1.3V, the output current is regulated to: VIN R1 R3 R2 R4 OVLO EN/UVLO 37911 F08 Figure 8.
PAGE 17
LT3791-1 Applications Information IIN = Dimming Control 50mV RIN For loop stability a lowpass RC filter is needed. For most applications, a 50Ω resistor and 470nF capacitor is sufficient. Table 3 RIN (mΩ) 20 15 12 10 6 5 4 3 2 ILIMIT (A) 2.5 3.3 4.2 5.0 8.3 10.0 12.5 16.7 25 IVINMON The IVINMON pin provides a linear indication of the current flowing through the input. The equation for VIVINMON is V(IVINP-IVINN) • 20.
PAGE 18
LT3791-1 Applications Information Soft-Start Soft-start reduces the input power sources’ surge currents by gradually increasing the controller’s current limit (proportional to an internally buffered clamped equivalent of VC). The soft-start interval is set by the soft-start capacitor selection according to the following equation t SS = 1.2V •C 14µA SS A 100k resistor must be placed between SS and VREF for the LT3791-1. This 100k resistor also contributes the extra SS charge current.
PAGE 19
LT3791-1 Applications Information From a known power dissipated in the power MOSFET, its junction temperature can be obtained using the following formula: TJ = TA + P • RTH(JA) The RTH(JA) to be used in the equation normally includes the RTH(JC) for the device plus the thermal resistance from the case to the ambient temperature (RTH(JC)). This value of TJ can then be compared to the original, assumed value used in the iterative calculation process. ρT NORMALIZED ON-RESISTANCE (Ω) 2.0 1.5 1.
PAGE 20
LT3791-1 Applications Information Efficiency Considerations The power efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Although all dissipative elements in circuits produce losses, four main sources account for most of the losses in LT3791-1 circuits: 1. DC I2R losses.
PAGE 21
LT3791-1 Applications Information n n n n The path formed by switch M1, switch M2, D1 and the CIN capacitor should have short leads and PC trace lengths. The path formed by switch M3, switch M4, D2 and the COUT capacitor also should have short leads and PC trace lengths. n n The output capacitor (–) terminals should be connected as close as possible to the (–) terminals of the input capacitor. Connect the top driver bootstrap capacitor, C1, closely to the BST1 and SW1 pins.
PAGE 22
LT3791-1 Typical Applications 98% Efficient 60W (12V 5A) Voltage Regulator Runs Down to 3V VIN RIN 0.003Ω VIN 3V TO 55V STARTS UP FROM 5.5V R7 50Ω D5 D6 INTVCC VIN C3 1µF BST2 IVINP IVINN TG1 TEST1 EN/UVLO BG1 INTVCC R9 100k R10 200k RFAULT 100k M2 D4 + VO M4 L1, 6.8µH COUT2 100µF 35V ROUT 0.015Ω COUT 10µF 25V ×3 M3 D3 VOUT 12V 5A R5 73.2k R6 8.06k SNSP RSENSE 0.004Ω LT3791-1 SNSN SHORT C/10 CCM IVINMON PGND BG2 SW2 TG2 ISP ISN FB ISMON CLKOUT PWMOUT VREF C8 0.
PAGE 23
LT3791-1 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev C) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 4.50 REF 2.74 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.50 – 0.75 (.020 – .030) 0.09 – 0.20 (.0035 – .
PAGE 24
LT3791-1 Typical Application 2.5A Buck-Boost 36V SLA Battery Charger PVIN 9V TO 58V RIN 0.003Ω 1µF 50Ω VIN INTVCC D1 TG1 IVINP INTVCC 200k 30.9k BG1 LT3791-1 SHORT PWMOUT TEST1 CHARGE CURRENT CONTROL RBAT 0.04Ω SNSN + PGND IVINMON ISMON CTRL BG2 SW2 TG2 FB ISP PWM ISN C/10 SS CCM RT VREF SYNC VC D1, D2: BAT46WJ 22nF L1: COILCRAFT SER2915L-103K M1-M4: RENESAS RJK0651DPB M5: NXP NX7002AK CIN2: NIPPON CHEMI-CON EMZA630ADA101MJA0G COUT2: SUNCON 35HVT220M M3 RSENSE 0.