LTC3726 Linear Technology, LTC3726 Datasheet

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LTC3726

Manufacturer Part Number
LTC3726
Description
Secondary-Side Synchronous Forward Controller
Manufacturer
Linear Technology
Datasheet

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Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LTC3726EGN
Manufacturer:
LT
Quantity:
10 000
Part Number:
LTC3726EGN#PBF
Manufacturer:
LT
Quantity:
20 000
Part Number:
LTC3726EGN#TRPBF
Manufacturer:
LINEAR/凌特
Quantity:
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Part Number:
LTC3726IGN
Manufacturer:
LT
Quantity:
10 000
Part Number:
LTC3726IGN#PBF
Manufacturer:
LT
Quantity:
1 600
Part Number:
LTC3726IGN#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Part Number:
LTC3726IGN#TRPBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
APPLICATIO S
FEATURES
TYPICAL APPLICATIO
V
V
IN
IN
+
Secondary-Side Control for Fast Transient Response
Self-Starting Architecture Eliminates Need for
Separate Bias Regulator
Proprietary Gate Drive Encoding Scheme Reduces
System Complexity
Current Mode Control Ensures Current Sharing
PLL Fixed Frequency: 100kHz to 500kHz
±1% Output Voltage Accuracy
OPTI-LOOP Compensation
Available in a Narrow 16-Lead SSOP Package
Isolated 48V Telecommunication Systems
Internet Servers and Routers
Distributed Power Step-Down Converters
Automotive and Heavy Equipment
365k
15k
1%
1%
1µF
100V
x3
33nF
2.2µF
25V
FQT7N10
U
UVLO
V
SS/FLT
NDRV
CC
100k
BAS21
Si7852DP
GND PGND VSLMT
BOOST
0.22µF
LTC3705
TG
U
TS BG IS
36V-72V to 3.3V/20A Isolated Forward Converter
Si7852DP
MURS120
FB/IN
FS/IN
+
L1: COILCRAFT SER2010-122
T1: PULSE PA0807
T2: PULSE PA0297
30mΩ
1W
162k
T2
MURS120
T1
Si7336ADP
1µF
2mΩ
33nF
2W
DESCRIPTIO
Secondary-Side Synchronous
The LTC
nous forward converters. When used in conjunction with
the LTC3705/LTC3725 gate driver and primary-side con-
trollers, the part creates a complete isolated power supply
that combines the simplicity of OPTI-LOOP
tion with the speed of secondary-side control.
The LTC3726 has been designed to simplify the design of
highly efficient, secondary-side forward converters. Work-
ing in concert with the LTC3705 or LTC 3725, the LTC3726
forms a robust, self-starting converter that eliminates the
need for the separate bias regulator that is commonly used
in secondary-side control applications. In addition, a pro-
prietary scheme is used to multiplex gate drive signals and
DC bias power across the isolation barrier through a
single, tiny pulse transformer.
The LTC3726 is available in a 16-lead SSOP package.
OPTI-LOOP is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6144194. Other patents pending.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
I
I
PT
PT
RUN/SS
S
S
+
+
FG
®
3726 is a secondary-side controller for synchro-
GND
SW SG
PGND
LTC3726
U
Forward Controller
Si7336ADP
×2
CMPSH1-4
V
SLP
CC
10µF
25V
FB/PHASE
FS/SYNC
MODE
1.2Ω
ITH
7.5V
www.DataSheet4U.com
1.2µH
L1
5k
680pF
20k
FZT690B
LTC3726
2.2µF
®
compensa-
102k
1%
22.6k
1%
3726 TA01
330µF
6.3V
×3
3726fb
1
V
V
OUT
OUT
+

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LTC3726 Summary of contents

Page 1

... The LTC3726 has been designed to simplify the design of highly efficient, secondary-side forward converters. Work- ing in concert with the LTC3705 or LTC 3725, the LTC3726 forms a robust, self-starting converter that eliminates the need for the separate bias regulator that is commonly used in secondary-side control applications ...

Page 2

... SW ............................................................... –5V to 50V ITH, RUN/SS ............................................... – 0. All Other Pins ............................................ – 0.3V to 10V Operating Ambient Temperature Range (Note 2) LTC3726EGN ...................................... – 40°C to 85°C LTC3726IGN ....................................... – 40°C to 85°C Operating Junction Temperature (Note 3) ........... 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ...

Page 3

... Refer to the Applications Information section for details. Note 4: The LTC3726 is tested in a feedback loop that servos V voltage near the internal 0.6V reference voltage to obtain the specified ITH voltage (V = 1.2V). ITH Note 5: Operating supply current is measured in test mode. Dynamic supply current is higher due to the internal gate charge being delivered at the switching frequency ...

Page 4

... LTC3726 W U TYPICAL PERFOR A CE CHARACTERISTICS V Supply Current vs CC Input Voltage 200kHz OSC ALL GATES LOAD INPUT VOLTAGE (V) 3726 G01 IS Pins Source Current 400 300 200 100 CT-MODE –100 –200 RS-MODE –) –300 ...

Page 5

... VOLTAGE (V) CC 3726 G12 Load Step (Figure 5) V OUT 100mV/DIV V = 72V IN I OUT 10A/DIV OUT LOAD STEP = 0A TO 20A 3726 G17 LTC3726 www.DataSheet4U.com Undervoltage Lockout vs Temperature 4.65 4.60 V RISING CC 4.55 4.50 4.45 4.40 4.35 4.30 4.25 30 – – TEMPERATURE (°C) 3726 G11 = 7V – ...

Page 6

... LTC3726 CTIO S SG (Pin 1): Gate Drive for the “Synchronous” MOSFET. FG (Pin 2): Gate Drive for the “Forward” MOSFET. MODE (Pin 3): Tie to either GND or V maximum duty cycle at either 50% or 75% respectively. Tie to ground through either a 200k or 100k resistor (50% or 75% maximum duty cycle) to disable pulse encoding ...

Page 7

... I TRP C RESET DOMINANT – WAIT R OVP DMAX SKIP C – BLANK + – 3.2V OVERCURRENT BLANK DMAX UVLO V REG 4V CCUV SB LTC3726 www.DataSheet4U.com WAIT PWM + OVP – ZERO CROSSING DETECT DRIVER PGND ENCODING V AND CC LOGIC DRIVE TYPE V 1.24V REF ...

Page 8

... CLK PER Figure 1: Gate Drive Encoding Scheme (V Self-Starting Architecture When the LTC3726 is used in conjunction with the LTC3705/ LTC3725 primary-side controller and gate driver, a com- plete self-starting isolated supply is formed. When input voltage is first applied in such an application, the LTC3705/ LTC3725 will begin switching in an “open-loop” fashion, causing the main output to slowly ramp upwards ...

Page 9

... Table 2 summarizes the operation of the FS pin. For synchronization between multiple LTC3726s, the PT SLOPE (D > 0.5) pin of one LTC3726 can be used as a master clock 0.1 • I • f SMAX OSC reference and tied to the FS pin of the other LTC3726s. None Table 2 0.2 • I • f SMAX OSC 0.3 • I • ...

Page 10

... When fully charged, the RUN/SS voltage remains at 3V. In the event that the sensed switch or inductor current exceeds the overcurrent trip threshold, an internal fault latch is tripped. When such a fault is detected, the LTC3726 immediately goes to zero duty cycle and initiates a soft- start retry. Prior to discharging the soft-start capacitor, ...

Page 11

... Second, the LTC3705/LTC3725 contains a time-out fea- ture that will detect a FAULT if the LTC3726 fails to start up and deliver PWM signals to the primary side. Finally, the LTC3726 has an independent overvoltage detection circuit that will crowbar the output of the DC/DC converter using the synchronous MOSFET switch ...

Page 12

... CC circuit of Figure 2 uses a peak detector followed by a simple linear regulator to rapidly develop a V the LTC3726. Note that this bias voltage must rise faster than the open-loop soft-start that is initiated by the LTC3705/LTC3725. This ensures that the LTC3726 be- gins switching and assumes control of the soft-start before the output voltage has risen substantially ...

Page 13

... U U APPLICATIO S I FOR ATIO the LTC3726) can be used as the input to the peak charge circuit of Figure 2. For lower output voltages, however normally necessary to use a dedicated bias winding to generate adequate bias voltage for the LTC3726. Current Sensing The LTC3726 provides considerable flexibility in cur- rent sensing techniques ...

Page 14

... For the LTC3726, the master performs soft-start and voltage-loop regulation by driving all slaves to the same current as the master using the ITH pins. Faults and shutdowns are communicated via the interconnection of the RUN/SS pins. The LTC3726 is put into slave mode by tying the FB pin ...

Page 15

... BSC .015 ± .004 × 45 ° .0532 – .0688 (0.38 ± 0.10) (1.35 – 1.75) 0 ° – 8 ° TYP .008 – .012 (0.203 – 0.305) TYP LTC3726 www.DataSheet4U.com .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – ...

Page 16

... Synchronous Controller Synchronous, Single Inductor, No Schottky Diode Required 2.5V ≤ V ≤ 36V Excellent Transient Response Use with LTC3726, Isolated Power Supplies, High Speed Gate Drivers Scalable Output Power; Self-Starting Architecture Synchronous; ZVS Operation; 24-Pin SSOP On-Chip Gate-Driver; Fast Startup www.linear.com ● ...

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