LT3804 Datasheet, PDF (1/16 Pages) Linear Technology – Secondary Side Dual Output Controller with Opto Driver

Final Electrical Specifications
LT3804
Secondary Side Dual
Output Controller with Opto Driver
FEATURES
DESCRIPTIO
June 2003
s _{Regulates Two Secondary Outputs}
s _{Optocoupler Feedback Driver and Second Output}
Synchronous Driver Controller
s _{True Differential Remote Sensing Regulation}
s _{High Switching Frequency: up to 800kHz}
s _{Programmable Current Limit}
s _{Programmable Soft-Start and Power Good}
s _{Automatic Frequency Synchronization}
s _{Available in Thermally Enhanced 28-Lead TSSOP}
U
APPLICATIO S
s _{48V Input Isolated DC/DC Converters}
s _{Multiple Output Power Supplies}
s _{Offline Converters}
s _{DC/DC Power Modules}
, LTC and LT are registered trademarks of Linear Technology Corporation.
The LT^®3804 is a high efficiency step-down switching
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.
TYPICAL APPLICATIO
V_IN
36V
TO 72V
TG BG
LT3781
SG
V_C
+ ^VREF
– ^VFB
L1
V_CC
1.8µH
BIAS
0.003Ω
••
Q4
Q3
x2
OUT2
LTC1693-1
OUT1
IN1 IN2
390pF
••
••
V_OS1^–
V_OS1⁺
2.74k
604Ω
LT3804
CL1N SYNC
CL1P TGATE
V_CC
SW
CSET BGATE
PGND
GNDS1
CL2P
CL2N
V_AOUT2
V_FB1
V_FB2
V_AOUT1
1.5k
GNDS2
OPTO
Q1
L2
1.8µH
Q2
x2
+ ^VOS1+
V_OS1^–
V_OUT1
3.3V
AT 15A
C_OUT1
0.003Ω
V_OUT2
1.8V
AT 15A
+
C_OUT2
3.01k
3804 F01
ISOLATION
BOUNDARY
C_OUT1, C_OUT2: SANYO POSCAP 4TPE680MF 680µF/4V
L1, L2: SUMIDA CEP125-IR8MC-H
Q1-Q4: SILICONIX Si7892DP
Figure 1. 250kHz, 3.3V and 1.8V Output Isolated DC/DC Converter (Simplified Schematic)
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.
3804i
1