lt3804 Linear Technology Corporation, lt3804 Datasheet

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lt3804

Manufacturer Part Number
lt3804
Description
Secondary Side Dual Output Controller With Opto Driver
Manufacturer
Linear Technology Corporation
Datasheet

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Part Number
Manufacturer
Quantity
Price
Part Number:
lt3804EFE
Manufacturer:
LT
Quantity:
81
FEATURES
APPLICATIO S
TYPICAL APPLICATIO
, LTC and LT are registered trademarks of Linear Technology Corporation.
Regulates Two Secondary Outputs
Optocoupler Feedback Driver and Second Output
Synchronous Driver Controller
True Differential Remote Sensing Regulation
High Switching Frequency: up to 800kHz
Programmable Current Limit
Programmable Soft-Start and Power Good
Automatic Frequency Synchronization
Available in Thermally Enhanced 28-Lead TSSOP
48V Input Isolated DC/DC Converters
Multiple Output Power Supplies
Offline Converters
DC/DC Power Modules
TO 72V
V
C
TG
36V
V
LT3781
IN
+
BG
U
V
V
Figure 1. 250kHz, 3.3V and 1.8V Output Isolated DC/DC Converter (Simplified Schematic)
REF
FB
SG
BOUNDARY
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
ISOLATION
Q3
x2
U
Q4
BIAS
V
CC
C
L1, L2: SUMIDA CEP125-IR8MC-H
Q1-Q4: SILICONIX Si7892DP
OUT2
OUT1
Output Controller with Opto Driver
OUT1
IN1
LTC1693-1
, C
IN2
OUT2
1.8 H
V
V
L1
OS1
OS1
: SANYO POSCAP 4TPE680MF 680 F/4V
+
2.74k
390pF
0.003
DESCRIPTIO
The LT
regulator with optocoupler feedback control for regulating
multiple outputs in single-secondary winding isolated
power supplies.
The LT3804 contains an error amplifier and an optocoupler
driver to regulate the first (main) output. For the second
output regulation, the LT3804 contains a complete PWM
controller to drive dual synchronous N-channel MOSFETs.
With leading edge modulation, it operates with either
current or voltage mode control of the primary side. The
LT3804 is synchronized to the falling edge of the trans-
former secondary winding and can be used in single-
ended or double-ended isolated power converter topolo-
gies. A user selectable discontinuous conduction mode
improves light load efficiency.
True differential Kelvin sensing is used for each output
feedback amplifier to achieve high regulation accuracy
and design simplicity. Other features include soft start,
current limit and power good flags.
604
CL1N
CL1P
V
CSET
GNDS1
V
V
OPTO
CC
FB1
AOUT1
®
LT3804
3804 is a high efficiency step-down switching
V
GNDS2
BGATE
TGATE
PGND
AOUT2
SYNC
CL2P
CL2N
Secondary Side Dual
V
SW
FB2
1.5k
U
Q1
Q2
x2
Final Electrical Specifications
1.8 H
L2
3.01k
0.003
V
V
OS1
OS1
3804 F01
+
+
+
C
C
V
3.3V
AT 15A
V
1.8V
AT 15A
OUT1
OUT2
June 2003
OUT1
OUT2
LT3804
1
3804i

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lt3804 Summary of contents

Page 1

... N-channel MOSFETs. With leading edge modulation, it operates with either current or voltage mode control of the primary side. The LT3804 is synchronized to the falling edge of the trans- former secondary winding and can be used in single- ended or double-ended isolated power converter topolo- gies ...

Page 2

... BOOST Pin Voltage with Respect to GND Pin .......... 35V SYNC Pin Voltage (Note 2) ..................................... 30V GNDS1 Pin Voltage ................................................... 1V GNDS2 Pin Voltage ................................................... 1V Operating Junction Temperature Range LT3804E (Note 3) ..............................– 125 C Storage Temperature Range ..................– 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are any outputs, unless otherwise noted ...

Page 3

... TGATE I < 50mA BGATE 10nF Load 1nF Load Note 3: The LT3804E is guaranteed to meet performance specifications from Specifications over the – operating temperature range are assured by design, characterization and correlation with statistical process controls. LT3804 = 25V, no load CC ...

Page 4

... LT3804 W U TYPICAL PERFOR A CE CHARACTERISTICS Over Junction GBIAS GBIAS Temperature 8.1 – 7.9 7.8 125 C 7 (mA) GBIAS 3804 G01 FREQ vs V REF CC CC CSET = 500pF REF 0 –1 FREQ (V) CC 3804 G04 Switching Frequency vs ...

Page 5

... Node . When the first output is in current limit, CA1 Inverting Input pulls down V (0.6V referred to Exposed Pad (Pin 29): Signal Ground. Must be electrically REF2 connected on PCB. Output. A2 LT3804 ) allowing discontinous S2 Inverting Input (0.6V referred to REF1 pin to regulate the first output current. AOUT1 3804i ...

Page 6

... LT3804 W BLOCK DIAGRA 6 3804i ...

Page 7

... By gener- ating the auxiliary output(s) from the secondary winding of the main output, the LT3804 allows for parallel process- ing of the output power. This minimizes the main output inductor size and directly regulates the auxiliary output. ...

Page 8

... W U For accurate sensing results, GNDS1 and GNDS2 should stay within –0.1V and 0.1V referred to GND. Note that if either GNDS1 or GNDS2 is not connected, the LT3804 will be shut down. Power Good When both outputs reach between 90% and 110% of the programmed level, V required if the function is used) to signal power good. If ...

Page 9

... V V OUT1 FB1 1.7V V AOUT1 – 1.4V R14 V A1 600 + 1. 1.2V V REF1 0.6V V OPTO GNDS1 Figure 3. Optocoupler Driver LT3804 is the reference voltage that con- SS2 is from SS2 SS2 V OUT1 SHORT The REF2 reaches SS2 STARTUP OR SHORT RELEASE 3804 F03 3804i 9 ...

Page 10

... MOSFET package. The conduction power losses of the MOSFETs are where I is the maximum output current of LT3804 circuit and R LMAX DS(ON)M1 the top and bottom MOSFETs, respectively. The R must be determined with 6.5V gate drive at the expected operating temperature ...

Page 11

... U U APPLICATIO S I FOR ATIO Light Load Operation of Second Output If the BGS pin is grounded, the LT3804 stays in continuous mode independent of load condition except during soft- start operation (see the Soft-Start section). If the BGS pin is left open under light load, V RS2 BGATE will be turned off(see comparator CA2 of Block Diagram), and the LT3804 will enter discontinous mode operation ...

Page 12

... LT3804 U U APPLICATIO S I FOR ATIO A planar transformer PA0191 by Pulse Engineering is employed as the power transformer in this design. This transformer is constructed on a PQ20 core with nine turns of primary windings, two turns of secondary windings and seven turns of auxiliary windings for the LT3781 bias supply ...

Page 13

... U U APPLICATIO S I FOR ATIO W U LT3804 C V SGND PGND SENSE SS BG SYNC THERM BSTREF TG FSET REF VBST 5V 3804i 13 ...

Page 14

... Figure 4. 36V – 72V CCS R57 10k C47 1 F D14 C44 C36 D15 25 4 CMDSH-3 0.1 F 4.7 F CMDSH-3 16V 16V V BOOST CC 27 GBAIS LT3804 5 TGATE BGATE 20 CL2P 21 CL2N 15 V AOUT2 C39 R50 330pF 14 3.3k V FB2 C38 12 0.033 F GNDS2 11 PGIN2 3 ...

Page 15

... BSC 1 0 – 8 0.65 0.45 – 0.75 (.0256) BSC 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 LT3804 9.60 – 9.80* (.378 – .386) 4.75 (.187 2.74 (.108 ...

Page 16

... LT3804 RELATED PARTS PART NUMBER DESCRIPTION LT1339 High Power Synchronous DC/DC Controller LT1425 Isolated Flyback Switching Regulator LT1431 Programmable Reference LT1680 High Power DC/DC Step-Up Controller LT1725 General Purpose Isolated Flyback Controller LT1737 High Power Isolated Flyback Controller LT1950 PWM Controller for Forward, Flyback, ...

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