LT3782
2-Phase Step-Up
DC/DC Controller
FEATURES
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DESCRIPTIO
■
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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
CC
≥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 SSOP Package
The LT
®
3782 is a current mode two 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.
With 10V gate drive (V
CC
≥13V)
and 4A peak drive current,
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6144194.
APPLICATIO S
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Industrial Equipment
Telecom Infrastructure
Interleaved Isolated Power Supply
TYPICAL APPLICATIO
V
IN
10V TO 36V
V
CC
R6
825k
C
IN
10µF
50V
2x
R8
274k
1µF
RUN
50V 4A Boost Converter
L1
GBIAS1
GBIAS2
GBIAS
BGATE1
R
S1
0.004Ω
V
EE1
SLOPE
DELAY
R
FREQ
80k
DCL
R
SET
SS
0.1µF
V
C
13k
100pF
6.8nF
V
EE2
10Ω
SENSE1
+
SENSE1
–
SENSE2
+
SENSE2
–
FB
GND
10nF
10nF
R
F1
475k
10Ω
BGATE2
M2
Si7852dp
2x
R
S2
0.004Ω
D1
30BQ060
D2
30BQ060
C
OUT1
10µF
50V
2x
V
OUT
50V, 4A
+
C3 L2
2µF
M1
Si7852dp
2x
+
C
OUT2
220µF
R
SLOPE
59k
EFFICIENCY (%)
LT3782
L1, L2: PB2020.223
C
IN
, C
OUT1
: X7R, TDK
3782 TA01
R
F2
24.9k
U
Efficiency and Power Loss
vs Load Current
97
EFFICIENCY
95
V
IN
= 12V
POWER LOSS (W)
93
91
89
87
85
V
IN
= 12V
V
IN
= 24V
POWER LOSS
3
0
12
9
6
V
IN
= 24V
15
18
0
1
2
3
I
OUT
(A)
4
5
3782 TA01b
U
U
3782fa
1
LT3782
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SGATE2
SGATE1
NC
GND
SYNC
DELAY
DCL
SENSE1
+
SENSE1
–
V
CC
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
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
SS ................................................................– 0.3V to 6V
SENSE1
+
, SENSE2
+
, SENSE1
–
, SENSE2
–
................................................................– 0.3V to 2V
1
2
3
4
5
6
7
8
9
29
28 GBIAS
27 V
CC
26 NC
25 NC
24 VEE1
23 BGATE1
22 GBIAS1
21 GBIAS2
20 BGATE2
19 VEE2
18 NC
17 RUN
16 FB
15 V
C
ORDER PART
NUMBER
LT3782EFE
SLOPE 10
R
SET
11
SENSE2
–
12
13
SENSE2
+
FE PART
MARKING
LT3782EFE
SS 14
FE PACKAGE
28-LEAD PLASTIC SSOP
EXPOSED PAD (PIN 29) IS GND
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 38°C/ W
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 13V, R
SET
= 80k, operating maximum V
CC
= 24V, no load on any
outputs, unless otherwise noted.
PARAMETER
Overall
Supply Voltage (V
CC
)
Supply Current (I
VCC
)
Shutdown
RUN Threshold
RUN Threshold Hysteresis
Supply Current in Shutdown
RUN Pin Input Current
Voltage Amplifier gm
Reference Voltage (V
REF
)
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
6
TYP
MAX
40
UNITS
V
mA
V
mV
mA
µA
µA
V
V
µmho
µA
V
V
µA
µA
V
µA
3782fa
V
C
≤
0.5V (Switching Off), V
CC
≤
40V
2.3
11
2.45
80
0.4
40
●
16
2.6
0.65
90
–2
2.464
2.488
370
0.6
0.4
14
28
15
1V
≤
RUN
≤
V
REF
, V
CC
≤
30V
RUN
≤
0.3V, V
CC
≤
30V
V
RUN
= 2.3V
–0.5
2.42
2.4
200
2.44
260
0.2
1.5
0.35
8
13
11
20
10
Transconductance
Input Current I
FB
V
C
High
V
C
Low
Source Current I
VC
Sink Current I
VC
V
C
Threshold for Switching Off (BGATE1, BGATE2 Low)
Soft-Start Current I
SS
V
VC
= 1V,
∆I
VC
=
±2µA
V
FB
= V
REF
I
VC
= 0
I
VC
= 0
V
VC
= 0.7V – 1V, V
FB
= V
REF
– 100mV
V
VC
= 0.7V – 1V, V
FB
= V
REF
+ 100mV
●
●
●
0.3
6
V
SS
= 0.1V – 2.8V
2
U
W
U
U
W W
W
LT3782
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 13V, R
SET
= 80k, operating maximum V
CC
= 24V, no load on any
outputs, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
4
50
∆V
SENSE
= 0V
R
SET
= 130k
R
SET
= 80k
R
SET
= 40k
Rising Edge V
SYNC
R
SET
= 130k
R
SET
= 80k
R
SET
= 40k
R
SET
= 80k
V
FB
= V
REF
– 25mV, R
SET
> 80K
R
SET
= 40K
R
SET
= 80k , V
DCL
≤
0.3V
V
DCL
= 1.2V
V
DCL
= V
RSET
V
DCL
= 0.3V
I
GBIAS
< 70mA
13V
≤
V
CC
≤
24V, I
BGATE
= –100mA
V
CC
= 8V, I
BGATE
= –100mA
Capacitive Load >22µF
Capacitive Load >50µF
8V
≤
V
CC
≤
24V, I
BGATE
= 100mA
Capacitive Load >22µF
Capacitive Load >50µF
8V
≤
V
CC
≤
24V, I
SGATE
= –20mA
8V
≤
V
CC
≤
24V, I
SGATE
= 20mA
500pF Load
DELAY Pin and R
SET
Pin Shorted
V
DELAY
= 1V
V
DELAY
= 0.5V
V
DELAY
= 0.25V
V
DELAY
= 0.25V
●
●
●
●
●
●
●
●
●
●
●
●
ELECTRICAL CHARACTERISTICS
MAX
UNITS
Current Amplifier CA1, CA2
Voltage Gain
∆V
C
/∆V
SENSE
Current Limit (V
SENSE1+
– V
SENSE1–
) (V
SENSE2+
– V
SENSE2–
)
Input Current (I
SENSE1+
, I
SENSE1–
, I
SENSE2+
, I
SENSE2–
)
Oscillator
Switching Frequency
130
212
386
0.8
180
290
550
2.3
90
83
94
90
50
75
Max Duty Cycle
–0.1
10.2
7.8
3.8
11
9.2
5
3
4
0.5
3
4
4.5
5.5
0.5
100
100
150
250
500
–0.1
–0.3
6.7
0.7
0.7
–0.3
11.7
10.5
154
250
465
1.2
177
288
533
2
240
392
715
kHz
kHz
kHz
V
kHz
kHz
kHz
V
%
%
%
%
µA
V
V
V
A
A
V
A
A
V
V
mA
ns
ns
ns
ns
µA
62
60
80
mV
µA
Synchronization Pulse Threshold on SYNC Pin
Synchronization Frequency Range
(Note: Operation Switching Frequency Equals
Half of the Synchronization Frequency)
V
RSET
Maximum Duty Cycle
Duty Cycle Limit
DCL Pin Input Current
Gate Driver
V
GBIAS
BGATE1, BGATE2 High Voltage
BGATE1, BGATE2 Source Current (Peak)
BGATE1, BGATE2 Low Voltage
BGATE1, BGATE2 Sink Current (Peak)
SGATE1, SGATE2 High Voltage
SGATE1, SGATE2 Low Voltage
SGATE1, SGATE2 Peak Current
Delay of BGATE High
Delay Pin Input Current
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.
Note 3:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
3782fa
3
LT3782
TYPICAL PERFOR A CE CHARACTERISTICS
V
GBIAS
vs I
GBIAS
11.0
10.9
10.8
10.7
20
18
16
14
I
CC
(mA)
12
10
8
6
4
2
0
50
I
GBIAS
(mA)
3782 G01
V
GBIAS
(V)
10.6
10.5
10.4
10.3
10.2
10.1
10.0
100
∆V
REF
(mV)
Switching Frequency vs R
FREQ
600
REFERENCE VOLTAGE (V)
500
FREQUENCY (kHz)
2.440
2.438
2.436
2.434
V
GBIAS
(V)
400
300
200
100
0
20 40 60 80 100 120 140 160 180 200
R
FREQ
(kΩ)
3782 G04
SGATE (Low) to BGATE (High)
Delay vs V
DELAY
(R
SET
= 80k)
1000
900
105
MAXIMUM DUTY CYCLE (%)
800
DUTY CYCLE (%)
700
DELAY (ns)
600
500
400
300
200
100
0
0
0.5
1.5
1.0
V
DELAY
(V)
2.0
2.5
3782 G07
4
U W
T
A
= 25°C unless otherwise noted.
∆V
REF
vs V
CC
,
∆Frequency
vs V
CC
(R
SET
= 80k)
3
2
1
0
–1
–2
–3
–4
–5
∆Frequency
∆V
REF
12
10
8
6
4
2
0
–2
–4
6
9
12
15
18
V
CC
(V)
3782 G03
I
CC
vs V
CC
∆FREQUENCY
(kHz)
0
6
8 10 12 14 16 18 20 22 24 26 28 30
V
CC
(V)
3782 G02
21
24
27
30
Reference Voltage vs
Temperature
2.446
2.444
2.442
14
12
10
8
6
4
V
GBIAS
vs I
GBIAS
at Start-Up
(Charging 2µF)
800
V
GBIAS
700
600
500
400
300
I
GBIAS
2
0
200
100
0
250µ
500µ
TIME (s)
750µ
0
1m
3782 G06
I
GBIAS
(mA)
0
25
75
100
125
50
JUNCTION TEMPERATURE (°C)
150
3782 G05
–2
Switching Frequency vs Duty
Cycle
120
110
100
100
90
80
70
60
50
80
100
40
200
400
500
300
SWITCHING FREQUENCY (kHz)
600
3782 G08
Maximum Duty Cycle Limit vs
V
DCL
(R
SET
= 80k)
95
90
85
0
0.3
0.6
0.9
1.5
V
DCL
(V)
1.2
1.8
2.1
2.4
3782 G09
3782fa
LT3782
PI FU CTIO S
SGATE2 (Pin 1):
Second Phase Synchronous Drive Sig-
nal. An external driver buffer is needed to drive the top
synchronous power FET.
SGATE1 (Pin 2):
First Phase Synchronous Drive Signal.
An external driver buffer is needed to drive the top syn-
chronous power FET.
NC (Pin 3):
Not Connected. Can be connected to GND.
GND (Pin 4):
Chip Ground.
SYNC (Pin 5):
Synchronization Input. The pulse width can
range from 10% to 70%. Note that the operating frequency
is half of the sync frequency.
DELAY (Pin 6):
When synchronous drivers are used, the
programmable delay that delays BGATE turns on after
SGATE turns off.
DCL (Pin 7):
This pin programs the limit of the maximum
duty cycle. When connected to V
RSET
, it operates at natural
maximum duty cycle, approximately 90%.
SENSE1
+
(Pin 8):
First Phase Current Sense Amplifier
Positive Input. An RC filter is required across the current
sense resistor. Current limit threshold is set at 60mV.
SENSE1
–
(Pin 9):
First Phase Current Sense Amplifier
Negative Input. An RC filter is required across the current
sense resistor.
SLOPE (Pin 10):
A resistor from SLOPE to GND increases
the internal current mode PWM slope compensation.
R
SET
(Pin 11):
A resistor from R
SET
to GND sets the
oscillator charging current and the operating frequency.
SENSE2
–
(Pin 12):
Second Phase Current Sense Amplifier
Negative Input. An RC filter is required across the current
sense resistor.
SENSE2
+
(Pin 13):
Second Phase Current Sense Amplifier
Positive Input. An RC filter is required across the current
sense resistor. Current limit threshold is set at 60mV.
SS (Pin 14):
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.
V
C
(Pin 15):
The output of the gm error amplifier and the
control signal of the current loop of the current-mode
PWM. Switching starts at 0.7V, and higher V
C
voltages
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
RUN
is below 2.2V and goes to low bias current shutdown
mode when V
RUN
is below 0.3V.
NC (Pin 18):
Not Connected. Can be connected to GND.
VEE2 (Pin 19):
Gate Driver BGATE2 Ground. This pin
should be connected to the ground side of the second
current sense resistor.
BGATE2 (Pin 20):
Second Phase MOSFET Driver.
GBIAS2 (Pin 21):
Bias for Gate Driver BGATE2. Should be
connected to GBIAS or an external power supply between
12V to 14V. A bypass low ESR capacitor of 2µF or larger
is needed and should be connected directly to the pin to
minimize parasitic impedance.
GBIAS1 (Pin 22):
Bias for Gate Driver BGATE1. Should be
connected to GBIAS2.
BGATE1 (Pin 23):
First Phase MOSFET Driver.
VEE1 (Pin 24):
Gate Driver BGATE1 Ground. This pin
should be connected to the ground side of the second
current sense resistor.
NC (Pin 25):
Not Connected. Can be connected to GND.
NC (Pin 26):
Not Connected. Can be connected to GND.
V
CC
(Pin 27):
Chip Power Supply. Good supply bypassing
is required.
GBIAS (Pin 28):
Internal 11V regulator output for biasing
internal circuitry. Should be connected to GBIAS1 AND
GBIAS2.
EXPOSED PAD (Pin 29):
The exposed package pad is
fused to internal ground and is for heat sinking. Solder the
bottom metal plate onto expanded ground plane for opti-
mum thermal performance.
U
U
U
3782fa
5
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