LT3782 Linear Technology, LT3782 Datasheet

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LT3782

Manufacturer Part Number
LT3782
Description
2-Phase Step-Up DC/DC Controller
Manufacturer
Linear Technology
Datasheet

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APPLICATIO S
FEATURES
TYPICAL APPLICATIO
10V TO 36V
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
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 SSOP Package
Industrial Equipment
Telecom Infrastructure
Interleaved Isolated Power Supply
100pF
V
10µF
IN
50V
C
2x
IN
825k
274k
R6
R8
R
R
SLOPE
59k
80k
FREQ
0.1µF
U
13k
1µF
6.8nF
V
RUN
SLOPE
DELAY
DCL
R
SS
V
CC
CC
SET
C
≥13V
LT3782
GND
50V 4A Boost Converter
SENSE1
SENSE1
SENSE2
SENSE2
BGATE1
BGATE2
GBIAS1
GBIAS2
GBIAS
U
V
V
EE1
EE2
FB
+
+
10Ω
+
10nF
C3
2µF
0.004Ω
L1
L2
R
S1
10Ω
10nF
M1
Si7852dp
2x
30BQ060
D1
30BQ060
M2
Si7852dp
2x
R
0.004Ω
S2
D2
DESCRIPTIO
The LT
converter controller. Its high switching frequency (up to
500kHz) and 2-phase operation reduce system filtering
capacitance and inductance requirements.
With 10V gate drive (V
the LT3782 can drive most industrial grade high power
MOSFETs with high efficiency. For synchronous applica-
tions, the LT3782 provides synchronous gate signals with
programmable falling edge delay to avoid cross conduc-
tion 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 LT3782 is available in a thermally enhanced 28-lead
SSOP package.
3782 TA01
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6144194.
, LTC and LT are registered trademarks of Linear Technology Corporation.
R
475k
F1
L1, L2: PB2020.223
C
IN
®
R
24.9k
, C
C
10µF
50V
2x
3782 is a current mode two phase step-up DC/DC
F2
OUT1
OUT1
+
: X7R, TDK
C
220µF
OUT2
V
50V, 4A
OUT
DC/DC Controller
U
2-Phase Step-Up
CC
≥13V) and 4A peak drive current,
97
95
93
91
89
87
85
0
Efficiency and Power Loss
EFFICIENCY
1
vs Load Current
2
I
OUT
V
V
IN
IN
(A)
POWER LOSS
= 12V
= 12V
3
LT3782
V
V
IN
4
IN
= 24V
= 24V
3782 TA01b
5
3782fa
1
18
15
12
9
6
3
0

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LT3782 Summary of contents

Page 1

... With 10V gate drive (V the LT3782 can drive most industrial grade high power MOSFETs with high efficiency. For synchronous applica- tions, the LT3782 provides synchronous gate signals with programmable falling edge delay to avoid cross conduc- tion when using external MOSFET drivers ...

Page 2

... NUMBER LT3782EFE VEE1 23 BGATE1 22 GBIAS1 29 GBIAS2 21 20 BGATE2 19 VEE2 PART RUN 17 MARKING LT3782EFE = 38° http://www.linear.com/leadfree/ = 24V, no load on any CC MIN TYP MAX ● ● 2.3 2.45 2.6 80 0.4 0. ● –0.5 –2 2.42 2.44 2.464 ● 2.4 2.488 ● ...

Page 3

... Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3782 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 125°C operating temperature range are assured by design, characterization and correlation with statistical process controls ...

Page 4

... LT3782 W U TYPICAL PERFOR A CE CHARACTERISTICS GBIAS GBIAS 11.0 10.9 10.8 10.7 10.6 10.5 10.4 10.3 10.2 10.1 10 100 I (mA) GBIAS 3782 G01 Switching Frequency vs R FREQ 600 500 400 300 200 100 100 120 140 180 0 80 160 200 R (kΩ) FREQ 3782 G04 SGATE (Low) to BGATE (High) ...

Page 5

... PWM. Switching starts at 0.7V, and higher V corresponds to higher inductor current. FB (Pin 16): Error Amplifier Inverting Input. A resistor divider to this pin sets the output voltage. RUN (Pin 17): LT3782 goes into shutdown mode when V is below 2.2V and goes to low bias current shutdown RUN mode when V NC (Pin 18): Not Connected ...

Page 6

... LT3782 W BLOCK DIAGRA – 1V AND CLAMPED AT 11V C GBIAS REGULATOR 20µF + LOW POWER SHUTDOWN R6 A5 RUN – 0. – + 2.44V BGATE1 SGATE1 DELAY SET SET SLOPE CH1 SLOPE 10 COMP S R SYNC 5 R SET 11 OSC CK Q LOGIC FREQ ...

Page 7

... RUN pin to set the desired V undervoltage lockout voltage. A 120mV hysteresis is built to turn the in on RUN pin thresholds. C Oscillation Frequency Setting and Synchronization The switching frequency of LT3782 can be set up to 500kHz by a resistor R For f SET Once the switching frequency f found from the Switching Frequency vs R found under the Typical Electrical Characteristics section ...

Page 8

... For high output voltage applications, the power loss of the catch diodes are relatively small because of high duty cycle. If diodes power loss or heat is a concern, the LT3782 provides PWM signals through SGATE1 and SGATE2 pins to drive external MOSFET drivers for synchronous rectifier operation ...

Page 9

... In a boost circuit, a power inductor should be designed to carry the maximum input DC current. The inductance should be small enough to generate enough ripple current to provide adequate signal to noise ratio to the LT3782. An empirical starting of the inductor ripple current (per phase) is about 40% of maximum DC current, which is half of the input DC current in a 2-phase circuit: ∆ ...

Page 10

... TH(JC) TH(JA) The gate drive voltage is set by the 10V GBIAS regulator. Consequently, 10V rated MOSFETs are required in most high voltage LT3782 applications. Pay close attention to the BV DSS MOSFETs relative to the maximum actual switch voltage in the application. The switch node can ring during the turn- off of the MOSFET due to layout parasitics ...

Page 11

... Thus the 2-phase technique signifi- cantly reduces the output capacitor size. 0.8 1.0 3782 F04 Figure 6. Normalized Output Ripple Currents in Boost Converter: 1-Phase and 2-Phase. I LT3782 • s Normalized Output RMS Ripple Currents 3 ...

Page 12

... 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 the circuit produce losses, four main sources usually account for the majority of the losses in LT3782 application circuits ...

Page 13

... Use a local via to ground plane for all pads that connect to ground. Use multiple vias for power components. Connect the current sense inputs of LT3782 directly to the current sense resistor pads. Connect the current sense traces on the opposite sides of pads from the traces carrying the MOSFETs source currents to ground ...

Page 14

... SENSE2 14 SS 4.7nF 14 10V to 24V Input to 24V, 8A Output Boost Converter 10V TO 24V INPUT 28 GBIAS 2R2 1µ EE1 23 BGATE1 22 GBIAS1 21 GBIAS2 LT3782 2.2µF 20 BGATE2 19 V EE2 825k 18 NC 274k 17 RUN 24. 221k 6.8nF C2 13 ...

Page 15

... BSC 0.195 – 0.30 (.0077 – .0118) 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT3782 9.60 – 9.80* (.378 – .386) 4.75 (.187 ...

Page 16

... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● V INA 0V TO 28V* 28 GBIAS 2R2 BAS516 26 NC 1µ EE1 23 BGATE1 22 GBIAS1 21 + GBIAS2 LT3782 2.2µF 20 – BGATE2 19 V EE2 825k 18 NC 274k 17 – RUN 24. BAS516 FB 261k INB ...

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