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LTC3705EGN#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
LTC3705
1
3705fb
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
■
Isolated 48V Telecommunication Systems
■
Internet Servers and Routers
■
Distributed Power Step-Down Converters
■
Automotive and Heavy Equipment
■
High-Speed Top and Bottom Gate Drivers for
2-Switch Forward Converter
■
On-Chip Rectifier and Self-Starting Architecture
Eliminate Need for Separate Gate Drive Bias
Supply
■
Wide Input Voltage Supply Range: 18V to 80V
■
Tolerant of 100V Input Voltage Transients
■
Linear Regulator Controller for Fast Start-Up
■
Precision UVLO with Adjustable Hysteresis
■
Overcurrent Protection
■
Volt-Second Limit Prevents Transformer Core
Saturation
■
Voltage Feedforward for Fast Transient Response
■
Available in 16-Lead Narrow SSOP Package
2-Switch Forward
Controller and Gate Driver
The LTC
®
3705 is a controller for a 2-switch forward
converter and includes on-chip bottom and top gate
drivers that do not require external transformers.
For secondary-side control, combine the LTC3705 with
the LTC3706 PolyPhase
®
secondary-side synchronous
forward controller to create a complete forward converter
using a minimum of discrete parts. A proprietary scheme
is used to multiplex gate drive signals across the isolation
barrier through a tiny pulse transformer. The on-chip
rectifier and the same pulse transformer provide gate drive
bias power.
Alternatively, the LTC3705 can be used as a standalone
voltage mode controller in a primary-side control architec-
ture with optoisolator feedback. Voltage feedforward pro-
vides excellent line regulation and transient response.
NDRV
GND PGND VSLMT
UVLO
BOOST
LTC3705
BAS21
FQT7N10
0.22µF
10µF
CMPSH1-4
1.2Ω
L1
1.2µH
TG TS BG IS
T2
1µF
162k
L1: COILCRAFT SER2010-122
T1: PULSE PA0807
T2: PULSE PA0297
33nF
30mΩ
1W
2mΩ
2W
Si7336ADP
Si7336ADP
×2
T1
••
MURS120
Si7852DP
Si7852DP
MURS120
V
CC
33nF
15k
365k
100k
2.2µF
SS/FLT
FB/IN
+
FS/IN
–
V
IN
–
V
IN
+
330µF
6.3V
×3
2.2µF
680pF
CZT3019
22.6k
20k
102k
V
OUT
–
3705 TA01
V
OUT
+
••
1µF
100V
x3
FG SW SG V
IN
NDRV V
CC
GND PGND PHASE SLP MODE REGSD
PT
+
I
S
+
I
S
–
PT
–
RUN/SS
LTC3706
ITH
FB
FS/SYNC
36V –72V to 3.3V/20A Isolated 2-Switch Forward Converter
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
PolyPhase is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Patent Pending
LTC3705
2
3705fb
Power Supply (V
CC
) ...................................–0.3V to 15V
External NMOS Drive (NDRV) ....................– 0.3V to 20V
NDRV to V
CC
...........................................................
–0.3V to 5V
Bootstrap Supply (BOOST) ......................–0.3V to 115V
Top Source (TS) .......................................... -5V to 100V
BOOST to TS .............................................–0.3V to 15V
Soft-Start Fault, Feedback,
Frequency Set, Transformer
Inputs (SSFLT, FB/IN
+
, FS/IN
–
) ..................–0.3V to 15V
All Other Pins (V
SLMT
, I
S
, UVLO) .................– 0.3V to 5V
Peak Output Current <1µs (TG, BG)........................... 2A
Operating Ambient Temperature Range .. –40°C to 85°C
Operating Junction Temperature (Note 2) ............ 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
T
JMAX
= 125°C, θ
JA
= 110°C/W
LTC3705EGN
LTC3705IGN
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
BOOST
= 12V, GND = PGND = V
TS
= 0V, T
A
= 25°C, unless
otherwise noted.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
TOP VIEW
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GND
I
S
V
SLMT
UVLO
SSFLT
NDRV
FB/IN
+
FS/IN
–
TS
TG
BOOST
NC
NC
V
CC
BG
PGND
GN PART
MARKING
3705
3705I
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/
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
CC
Supply, Linear Regulator and Trickle Charger Shunt Regulator
V
CCOP
Operating Voltage Range 7 12 15 V
V
CCLR
Output Voltage Linear Regulator in Operation 8 V
I
NDRV
Current into NDRV Pin Linear Regulator in Operation 0.1 1 mA
t
r(VCC)
Rise Time of V
CC
Linear Regulator Charging (0.5V to 7.5V) 45 µs
I
NDRVTO
Linear Regulator Time Out Current Threshold Primary-Side Operation 0.27 mA
I
CC
Supply Current V
UVLO
= 1.5V, Linear Regulator in 1.4 2.1 mA
Operation (Note 3)
I
CCM
Maximum Supply Current V
UVLO
= 1.5V, Trickle Charger in Operation, 1.7 2.5 mA
V
CC
= 13.2V (Note 3)
V
CCSR
Maximum Supply Voltage Trickle Charger Shunt Regulator 14.25 15 V
I
CCSR
Minimum Current into NDRV/V
CC
Trickle Charger Shunt Regulator, V
CC
= 15V 10 mA
(Note 3)
Internal Undervoltage
V
CCUV
Internal Undervoltage Threshold V
CC
Rising 5.3 V
V
CC
Falling 4.7 V
Gate Drive Undervoltage
V
GDUV
Gate Drive Undervoltage Threshold V
CC
Rising (Linear Regulator) ● 7.2 7.4 7.7 V
V
CC
Rising (Trickle Charger) ● 13.1 13.4 14 V
V
CC
Falling ● 6.8 7.0 7.2 V
Undervoltage Lockout (UVLO)
V
UVLOR
Undervoltage Lockout Threshold Rising Rising ● 1.220 1.242 1.280 V
V
UVLOF
Undervoltage Lockout Threshold Falling Falling ● 1.205 1.226 1.265 V
LTC3705
3
3705fb
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
BOOST
= 12V, GND = PGND = V
TS
= 0V, T
A
= 25°C, unless
otherwise noted.
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Operating junction temperature T
J
(in °C) is calculated from the
ambient temperature T
A
and the average power dissipation PD (in watts)
by the formula: T
J
= T
A
+ θ
JA
• PD. Refer to the Applications Information
section for details.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
HUVLO
Hysteresis Current V
UVLO
= 1V ● 4.2 4.9 5.6 µA
V
UVLOOP
Voltage Feedforward Operating Range Primary-Side Control V
UVLOF(MIN)
3.75 V
Gate Drivers (TG and BG)
R
OS
Output Pull-Down Resistance I
OUT
= 100mA 1.9 Ω
V
OH
High Output Voltage I
OUT
= –100mA 11 V
I
PU
Peak Pull-Up Current 1.7 A
t
r
Output Rise Time 10% to 90%, C
OUT
= 4.7nF 40 ns
t
f
Output Fall Time 10% to 90%, C
OUT
= 4.7nF 70 ns
Rectifier
I
RECT
Maximum Rectifier DC Output Current 25 mA
Oscillator
f
OSC(P)
Oscillator Frequency Primary-Side Control, R
FS(P)
= 100kΩ 200 kHz
Primary-Side Control, R
FS(P)
= 25kΩ 700 kHz
Primary-Side Control, R
FS(P)
= 300kΩ 70 kHz
∆f
RFS(P)
Oscillator Resistor Set Accuracy Primary-Side Control
25k < R
FSET
< 300k ±15 %
f
OSC(S)
Oscillator Frequency Secondary-Side Control (During Start-Up), 300 kHz
R
FS(S)
= 100kΩ
Soft-Start/Fault (SSFLT)
I
SS(C)
Soft-Start Charge Current Primary-Side Control, V
SSFLT
= 2V –5.2 µA
Secondary-Side Control, V
UVLO
= 1.3V, –4 µA
V
SSFLT
= 2V
Secondary-Side Control, V
UVLO
= 3.75V, –1.6 µA
V
SSFLT
= 2V
V
LRTO
Linear Regulator Time Out-Threshold 3.9 V
V
FLTH
Fault Output High V
CC
= 8V 6.7 V
I
SS(D)
Soft-Start Discharge Current Timing Out After Fault, V
SSFLT
= 2V 1 µA
Current Sense Input (I
S
)
V
IS(MAX)
Overcurrent Threshold 300 mV
Volt Second Limit (V
SLMT
)
V
VSL(MAX)
Volt-Second Limit Threshold 1.26 V
I
VSLMT(MAX)
Maximum Volt-Second Limit Resistor Current 0.25 mA
Optoisolator Bias Current
V
OPTO
Open Circuit Optoisolator Voltage Primary-Side Control I
FB
= 0V 3.3 V
I
OPTO
Optoisolator Bias Current Primary-Side Control V
FB
= 2.5V 0.5 mA
Primary-Side Control V
FB
= 0V 1.6 mA
Note 3: I
CC
is the sum of current into NDRV and V
CC
.
Note 4: The LTC3705EGN is guaranteed to meet performance
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3705IGN is
guaranteed and tested over the – 40°C to 85°C operating temperature
range.
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LTC3705EGN#PBF

Mfr. #:
Buy LTC3705EGN#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Primary Side Controller
Lifecycle:
New from this manufacturer.
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