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PDF LTC3901 Data sheet ( Hoja de datos )
| Número de pieza | LTC3901 | |
| Descripción | Secondary Side Synchronous Driver for Push-Pull and Full-Bridge Converters | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3901
Secondary Side
Synchronous Driver for Push-Pull
and Full-Bridge Converters
FEATURES
■ N-Channel Synchronous MOSFET Driver
■ Programmable Timeout
■ Reverse Inductor Current Sense
■ Gate Drive Transformer Synchronization
Sequence Monitor
■ Wide VCC Supply Range: 4.5V to 11V
■ 15ns Rise/Fall Times at VCC = 5V, CL = 4700pF
■ Undervoltage Lockout
■ Small 16-Lead SSOP Package
U
APPLICATIO S
■ 48V Input Isolated DC/DC Converters
■ Isolated Telecom Power Supplies
■ Distributed Power Step-Down Converters
■ Industrial Control System Power Supplies
■ Automotive and Heavy Equipment
DESCRIPTIO
The LTC®3901 is a secondary side synchronous rectifier
driver designed to be used in isolated push-pull and full-
bridge converter power supplies. The chip drives two
external N-channel MOSFETs and accepts a transformer-
generated bipolar input to maintain sychronization with
the primary side controller.
The LTC3901 provides a full range of protection features
for the external MOSFETs. A programmable timeout func-
tion is included that disables both drivers when the syn-
chronization signal is missing or incorrect. Additionally,
the chip senses the output inductor current through the
drain-source resistance of the two MOSFETs, turning off
the MOSFETs if the inductor current reverses. The LTC3901
also shuts off the drivers if the supply is low or if the
synchronization sequence is incorrect.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
VIN
36V TO 72V
ISOLATION
BARRIER
T1
MA MB
ME
DRVA
DRVB
LTC3723
PUSH-PULL
CONTROLLER
COMP VFB SDRA SDRB
MF
T2
L1
CSE+
ME
CSE–
VCC
GND
LTC3901
CSF+
PVCC
MF
CSF–
PGND
SYNC TIMER
OUT FB
LT4430 OR LT1431
OPTOCOUPLER
DRIVER
COMP
Figure 1. Simplified Isolated Push-Pull Converter
+
COUT
VOUT
12V
3901 F01
3901f
1
1 page  
LTC3901
TYPICAL PERFOR A CE CHARACTERISTICS
VCC Supply Current vs
Temperature
20
CLOAD = 4.7nF
18
16 VCC = 11V
14
12
10
8 VCC = 5V
6
4
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3901 G15
VCC Supply Current
vs Load Capacitance
30
TA = 25°C
25
VCC = 11V
20
15
10
VCC = 5V
5
0
0 1 2 3 4 5 6 7 8 9 10
CLOAD (nF)
3901 G16
PI FU CTIO S
PVCC (Pin 1): Driver Supply Input. This pin powers the
ME and MF drivers. Bypass this pin to PGND using a 4.7µF
low ESR capacitor in close proximity to the LTC3901. This
pin should be connected to the same supply voltage as the
VCC pin.
ME (Pin 2, 3): Driver Output for ME. This pin drives the
gate of the external N-channel MOSFET, ME.
PGND (Pin 4,13): Power Ground. Both drivers return to
this pin. Connect PGND to a high current ground node in
close proximity to the sources of ME and MF.
CSE+, CSE– (Pin 6, 5): ME Current Sense Differential
Input. Connect CSE+ through a series resistor to the drain
of ME and CSE– through a series resistor to the source of
ME. The LTC3901 monitors the CSE inputs 250ns after ME
goes high. If the inductor current reverses and flows into
ME causing CSE+ to rise above CSE–by more than 10.5mV,
the LTC3901 pulls ME low. See the Current Sense section
for more details on choosing the resistance values for
RCSE1 to RCSE3.
TIMER (Pin 7): Timer Input. Connect this pin to an external
R-C network to program the timeout period. The LTC3901
resets the timer at every positive and negative transition of
the SYNC input. If the SYNC signal is missing or incorrect,
the LTC3901 pulls both ME and MF low once the TIMER
pin goes above the timeout threshold. See the Timer sec-
tion for more details on programming the timeout period.
GND (Pin 8,10): Signal Ground. All internal low power
circuitry returns to this pin. To minimize differential ground
currents, connect GND to PGND right at the LTC3901.
SYNC (Pin 9): Driver Synchronization Input. 0V at this pin
forces both ME and MF high after an initial negative pulse.
A subsequent positive pulse at SYNC input forces ME to
pull low, whereas a negative pulse forces MF to pull low.
The SYNC signal should alternate between positive and
negative pulses. If the SYNC signal is incorrect, the LTC3901
pulls both MF and ME low.
CSF+, CSF– (Pin 11, 12): MF Current Sense Differential
Input. Connect CSF+ through a series resistor to the drain
of MF and CSF– through a series resistor to the source of
MF. The LTC3901 monitors the CSF inputs 250ns after MF
goes high. If the inductor current reverses and flows into
MF causing CSF+ to rise above CSF– by more than 10.5mV,
the LTC3901 pulls MF low. See the Current Sense section
for more details on choosing the resistance values for
RCSF1 to RCSF3.
MF (Pin 14, 15): Driver Output for MF. This pin drives the
gate of the external N-channel MOSFET, MF.
VCC (Pin 16): Power Supply Input. All internal circuits
except the drivers are powered from this pin. Bypass this
pin to GND using a 1µF capacitor in close proximity to the
LTC3901.
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5 Page 
APPLICATIO S I FOR ATIO
VIN
MA
T3
MB
ISOLATION
BARRIER
MC
T4
T1
MD
LTC3901
L1
+ VOUT
L2 COUT
AB
CD
LTC3722-1
FULL-BRIDGE CONTROLLER
COMP VFB
EF
ME
the
MF
6 CSE+
3 ME
5 CSE–
16
VCC
8,10
GND
LTC3901
11 CSF+
14 MF
1
PVCC
12 CSF–
4,13
PGND
9
SYNC
7
TIMER
T2
OUT FB
OPTOCOUPLER
DRIVER
COMP
3901 F10
Figure 10. Simplified Isolated Full-Bridge Converter
MA
MB
MC
MD
E
F
SYNC
0V
ME
MF
3901 F11
Figure 11. Full-Bridge Converter Switching Waveforms
In the first period, MB turns off, E goes low (followed by
MA turning on), and the LTC3901 forces ME to turn off.
The primary side delivers power to the load through
MOSFET MF, T1 and L1.
In the second period, MA remains on, MD turns off, and
MC turns on. E goes high and the LTC3901 forces both ME
and MF to conduct. This is the free-wheeling period with
the T1 secondary output shorted.
In the third period, MA turns off, F goes low (followed by
MB turning on), and the LTC3901 forces MF to turn off.
The primary side delivers power to the load through
MOSFET ME, T1 and L2.
Like the second period, the last period is a free-wheeling
period. MB remains on, MC turns off, MD turns on, F goes
high, and the LTC3901 forces both ME and MF to conduct.
The timeout and current sense operations are the same as
in the push-pull application.
3901f
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3901.PDF ] | |
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