Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage regulators - DC DC switch controllers TSSOP 28 EP

LT3782A

3782afb

3782A TA01

6.8nF

13k

0.1µF

10nF

10µF

80k

59k

0.004

1µF

274k

825k

220µF

OUT

50V, 4A

10V TO 36V

2µF

20µH

0.004

LT3782A

RUN

SLOPE

DELAY

DCL

SET

GBIAS2

GBIAS

BGATE1

EE1

BGATE2

EE2

SENSE1

–

SENSE2

–

GND

GBIAS1

10

10nF

10

475k

D1, D2: 30BQ060PbF

Q1, Q2: Si7852DP-T1-E3

100pF

24.9k

10µF

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

2-Phase Step-Up

DC/DC Controller

The LT

3782A is a current mode 2-phase step-up DC/DC

converter controller. Its high switching frequency (up to

500kHz) and 2-phase operation reduce system ﬁ ltering

capacitance and inductance requirements.

With 10V gate drive (V

≥13V) and 4A peak drive current,

the LT3782A can drive most industrial grade high power

MOSFETs with high efﬁ ciency. For synchronous applica-

tions, the LT3782A provides synchronous gate signals

with programmable falling edge delay to avoid cross

conduction when using external MOSFET drivers. Other

features include programmable undervoltage lockout,

soft-start, current limit, duty cycle clamp (50% or higher)

and slope compensation. The LT3782A is identical to the

LT3782 except that the LT3782A has a tighter current sense

mismatch tolerance.

The LT3782A is available in thermally enhanced 28-lead

TSSOP and 4mm × 5mm QFN packages.

Industrial Equipment

Telecom Infrastructure

Interleaved Isolated Power Supply

2-Phase Operation Reduces Required Input and

Output Capacitance

Programmable Switching Frequency:

150kHz to 500kHz

6V to 40V Input Range

10V Gate Drive with V

≥13V

High Current Gate Drive (4A)

Programmable Soft-Start and Current Limit

Programmable Slope Compensation for

High Noise Immunity

MOSFET Gate Signals with Programmable

Falling Edge Delay for External Synchronous Drivers

Programmable Undervoltage Lockout

Programmable Duty Cycle Clamp (50% or Higher)

Thermally Enhanced 28-Lead TSSOP and 4mm × 5mm

QFN Packages

50V 4A Boost Converter Efﬁ ciency and Power Loss

vs Load Current

OUT

(A)

EFFICIENCY (%)

3782A TA01b

POWER LOSS (W)

= 12V

= 24V

EFFICIENCY

POWER LOSS

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks, ThinSOT

and No R

SENSE

are trademarks of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Protected by U.S. Patents including 6144194.

Summary of content (20 pages)

PAGE 1
LT3782A 2-Phase Step-Up DC/DC Controller DESCRIPTION FEATURES n n n n n n n n n n n The LT®3782A is a current mode 2-phase step-up DC/DC converter controller. Its high switching frequency (up to 500kHz) and 2-phase operation reduce system ﬁltering capacitance and inductance requirements.
PAGE 2
LT3782A ABSOLUTE MAXIMUM RATINGS (Note 1) VCC Supply Voltage ...................................................40V GBIAS, GBIAS1, GBIAS2 Pin (Externally Forced) ....................................................14V SYNC, RUN Pin .........................................................30V Operating Junction Temperature Range (Notes 2, 3) ................................. –40°C to 125°C SS ........................................................... 300μA Max ISS SENSE1+, SENSE2+, SENSE1–, SENSE2– .....
PAGE 3
LT3782A ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating junction temperature range, otherwise speciﬁcations are at TJ = 25°C. VCC = 13V, RSET = 80k, no load on any outputs, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Overall l Supply Voltage (VCC) Supply Current (IVCC) 6 VC ≤ 0.5V (Switching Off), VCC ≤ 40V 40 V 11 16 mA 2.45 2.6 Shutdown l RUN Threshold 2.
PAGE 4
LT3782A ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating junction temperature range, otherwise speciﬁcations are at TJ = 25°C. VCC = 13V, RSET = 80k, no load on any outputs, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Gate Driver VGBIAS IGBIAS < 70mA l 10.2 11 11.7 V BGATE1, BGATE2 High Voltage 13V ≤ VCC ≤ 24V, IBGATE = –100mA VCC = 8V, IBGATE = –100mA l l 7.8 3.8 9.2 5 10.
PAGE 5
LT3782A TYPICAL PERFORMANCE CHARACTERISTICS 600 2.446 CURRENT LIMIT THRESHOLD (mV) 70 2.444 REFERENCE VOLTAGE (V) 500 400 300 200 2.442 2.440 2.438 2.436 25 75 100 125 50 JUNCTION TEMPERATURE (°C) 0 3782A G04 64 61 58 150 –20 30 55 5 80 TEMPERATURE (°C) 105 130 3782A G10 3782A G05 SGATE (Low) to BGATE (High) Delay vs VDELAY (RSET = 80k) VGBIAS vs IGBIAS at Start-Up (Charging 2μF) 14 1000 800 12 67 55 –45 2.
PAGE 6
LT3782A PIN FUNCTIONS (FE/UFD) SGATE2 (Pin 1/Pin 26): Second Phase Synchronous Drive Signal. An external driver buffer is needed to drive the top synchronous power FET. SS (Pin 14/Pin 11): Soft-Start. A capacitor on this pin sets the output ramp up rate. The typical time for SS to reach the programmed level is (C • 2.44V)/10μA. SGATE1 (Pin 2/Pin 27): First Phase Synchronous Drive Signal. An external driver buffer is needed to drive the top synchronous power FET.
PAGE 7
LT3782A BLOCK DIAGRAM VIN VCC CIN 20μF 27 REGULATOR GBIAS1 + + LOW POWER SHUTDOWN R6 + A5 RUN 17 R8 A11 – + VOUT L1 15μH VGBIAS = VCC – 1V AND CLAMPED AT 11V A6 D2 + COUT 100μF C3 2μF 21 – + 7V 0.5V L2 15μH GBIAS2 A8 – + 22 D1 GBIAS 28 VCC – 2.5V RF1 + RF2 A7 – + A20 2.44V SGATE1 A4 2 A1 DELAY + + 6 ONE SHOT RSET A12 2.
PAGE 8
LT3782A APPLICATIONS INFORMATION Operation Soft-Start and Shutdown The LT3782A is a two phase constant frequency current mode boost controller. Switching frequency can be programmed up to 500kHz. During normal switching cycles, the two channels are controlled by internal ﬂip-ﬂops and are 180 degrees out-of-phase. During soft-start, the voltage on the SS pin (VSS) controls the output voltage. The output voltage thus ramps up following VSS . The effective range of VSS is from 0V to 2.44V.
PAGE 9
LT3782A APPLICATIONS INFORMATION With a 200ns one-shot timer on chip, the LT3782A provides ﬂexibility on the external sync pulse width. The sync pulse threshold is about 1.2V (Figure 1). This pin can be ﬂoated when the sync function is not used. Current Limit Current limit is set by the 63mV threshold across SEN1P, SEN1N for channel one and SEN2P, SEN2N for channel two. By connecting an external resistor RS (see Block Diagram), the current limit is set for 63mV/RS .
PAGE 10
LT3782A APPLICATIONS INFORMATION Slope Compensation The LT3782A is designed for high voltage and/or high current applications, and very often these applications generate noise spikes that can be picked up by the current sensing ampliﬁer and cause switching jitter. To avoid switching jitter, careful layout is absolutely necessary to minimize the current sensing noise pickup. Sometimes increasing slope compensation to overcome the noise can help to reduce jitter.
PAGE 11
LT3782A APPLICATIONS INFORMATION During the switch on-time, the control circuit limits the maximum voltage drop across the sense resistor to about 63mV. The peak inductor current is therefore limited to 63mV/R. The relationship between the maximum load current, duty cycle and the sense resistor RSENSE is: R ≤ VSENSE(MAX) • 1– DMAX I 1.
PAGE 12
LT3782A APPLICATIONS INFORMATION From a known power dissipated in the power MOSFET, its junction temperature can be obtained using the following formula: TJ = TA + PFET • RTH(JA) The RTH(JA) to be used in this equation normally includes the RTH(JC) for the device plus the thermal resistance from the case to the ambient temperature (RTH(CA)). This value of TJ can then be compared to the original, assumed value used in the iterative calculation process.
PAGE 13
LT3782A APPLICATIONS INFORMATION For a given VIN and VOUT, we can calculate the duty cycle D and then derive the output RMS ripple current from Figure 6. After choosing output capacitors with sufﬁcient RMS ripple current rating, we also need to consider the ESR requirement if electrolytic caps, tantulum caps, POSCAPs or SP CAPs are selected.
PAGE 14
LT3782A APPLICATIONS INFORMATION 3. The I2R losses in the sense resistor can be calculated almost by inspection: IO(MAX) 2 2 • R • DMAX PR(SENSE) = 1– DMAX 4. The losses in the inductor are simply the DC input current squared times the winding resistance. Expressing this loss as a function of the output current yields: IO(MAX) 2 2 • RW PR(WINDING) = 1– DMAX 5. Losses in the boost diode.
PAGE 15
LT3782A TYPICAL APPLICATIONS 10V to 24V Input to 24V, 8A Output Boost Converter 1 3 4 5 7 10Ω 8 CS1 SGATE1 VCC NC NC NC GND LT3782A VEE1 SYNC DELAY BGATE1 DCL GBIAS1 SENSE1+ GBIAS2 10V TO 24V INPUT 28 2R2 27 L1 PB2020-103 26 1μF 25 CS1 23 10 82k 11 21 CIN 22μF 25V BGATE2 SLOPE VEE2 NC RSET 12 SENSE2– RUN 13 SENSE2+ FB 14 VC SS 20 COUT1 22μF, 25V, ×4 OUTPUT 24V 8A 0.004Ω 19 CS2 18 825k 17 274k 16 24.
PAGE 16
R6 56.2k R5 23.7k R2 60.4k C4 22pF SENSE2– C9 2.2nF R1 10Ω SENSE1 + s2 10μF s2 SGATE1 SGATE2 SENSE2+ R3 10Ω C2 0.1μF SENSE1– C3 2.2nF + 330μF VIN 10V TO 14V 14 13 12 11 10 9 8 7 6 5 4 3 2 1 – SS SENSE2+ SENSE2 RSET SLOPE SENSE1– RUN GND VEE2 BGATE2 GBIAS2 GBIAS1 BGATE1 VEE1 GND GND VCC1 GBIAS 15 16 17 18 19 20 21 22 23 24 25 26 27 28 CC2 220pF VC FB = 2.
PAGE 17
LT3782A PACKAGE DESCRIPTION FE Package 28-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation EB 9.60 – 9.80* (.378 – .386) 4.75 (.187) 4.75 (.187) 28 2726 25 24 23 22 21 20 19 18 1716 15 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 SEE NOTE 4 0.45 ±0.05 EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 6.40 2.74 (.252) (.108) BSC 1.05 ±0.10 0.65 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1.
PAGE 18
LT3782A PACKAGE DESCRIPTION UFD Package 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 ±0.05 4.50 ± 0.05 3.10 ± 0.05 2.50 REF 2.65 ± 0.05 3.65 ± 0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 3.50 REF 4.10 ± 0.05 5.50 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ± 0.10 (2 SIDES) 0.75 ± 0.05 R = 0.05 TYP PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 2.50 REF R = 0.115 TYP 27 28 0.40 ± 0.
PAGE 19
LT3782A REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 2/10 Change Ambient Temp on FE Package 2 Changes to Order Information 2 Addition to Note 2 4 Change TA = 25°C to TJ = 25°C Changes to Pin Functions 6 Changes to Block Diagram 7 Changes to Typical Applications B 4/10 3, 4, 5 16, 20 Updated Related Parts 20 Add Part Numbers for D1, D2, Q1 and Q2 on Typical Application 1 Addition to Note 2 4 3782afb Information furnished by Linear Technology Corporation is believed to be acc
PAGE 20
LT3782A TYPICAL APPLICATION 28V Output Base Station Power Converter with Redundant Input 1 3 4 5 7 10Ω CS1 GBIAS VCC NC NC NC GND LT3782A VEE1 SYNC BGATE1 DELAY DCL GBIAS1 8 SENSE1+ GBIAS2 9 SENSE1– 25 L1 10μH BAS516 26 Q1 PH4840S 1μF CINA 22μF 24 CS1 23 COUT2 330μF, 35V, ×2 0.004Ω 10 82k 11 COUT1 10μF, 50V, ×4 VEE2 NC RSET 12 SENSE2– RUN 13 SENSE2+ FB 14 VC SS 20 0.004Ω 19 18 825k 17 274k 16 24.