LINEAR TECHNOLOGY LTC3901 Technical data

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

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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

LTC3901

Secondary Side

Synchronous Driver for Push-Pull

and Full-Bridge Converters

U

DESCRIPTIO

The LTC®3901 is a secondary side synchronous rectifier
driver designed to be used in isolated push-pull and full­bridge converter power supplies. The chip drives two
external N-channel MOSFETs and accepts a transformer­generated 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 func­tion is included that disables both drivers when the syn­chronization 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

V

IN

36V TO 72V

MA MB ME

DRVA DRVB

LTC3723

PUSH-PULL

CONTROLLER

COMP V

FB

U

ISOLATION

BARRIER

T1

+

CSE

ME

CSE

CSF

MF

SDRBSDRA

T2

MF

CSF

SYNC

OUT

LT4430 OR LT1431

V

–

GND

LTC3901

+

PV

–

PGND

TIMER

OPTOCOUPLER

DRIVER

COMP

CC

CC

L1

+

FB

C

3901 F01

OUT

V
12V

OUT

Figure 1. Simplified Isolated Push-Pull Converter

3901f

1

LTC3901

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

PV

CC

ME

ME

PGND

CSE

–

CSE

+

TIMER

GND

V

CC

MF

MF

PGND

CSF

–

CSF

+

GND

SYNC

ABSOLUTE AXI U RATI GS

(Note 1)

Supply Voltage

, PV

V

CC

Input Voltage

–

CSE

, CSF–, TIMER ................. –0.3V to (VCC + 0.3V)

SYNC ...................................................... –12V to 12V

Input Current

CSE+, CSF
Operating Temperature Range (Note 2) ...–40°C to 85°C

Storage Temperature Range ..................–65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

ELECTRICAL CHARACTERISTICS

temperature range. V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

V

UVLO

I

VCC

Timer

V

TMR

I

TMR

t

TMRDIS

V

TMRMAX

Current Sense (Note 5)

ICS+CS

ICS–CS

V

CSMAX

V

CS

SYNC Input

I

SYNC

V

SYNCP

V

SYNCN

Driver Output

R

ONH

R

ONL

I

PK

2

WW

W

............................................................................

CC

+

.....................................................................

= 5V, TA = 25°C unless otherwise specified. (Note 3)

CC

Supply Voltage Range ● 4.5 5 11 V

VCC Undervoltage Lockout Threshold Rising Edge ● 4.1 4.5 V
V

Undervoltage Lockout Hysteresis Rising Edge to Falling Edge 0.5 V

CC

VCC Supply Current V

Timer Threshold Voltage ● –10% VCC/5 10% V

Timer Input Current V

Timer Discharge Time C

Timer Pin Clamp Voltage C

+

Input Current VCS+ = 0V ● ±1 µA

–

Input Current VCS– = 0V ● ±1 µA

CS+ Pin Clamp Voltage IIN = 5mA, Driver Off 11 V

Current Sense Threshold Voltage VCS– = 0V 7.5 10.5 13.5 mV

SYNC Input Current V

SYNC Input Positive Threshold ● 1.0 1.4 1.8 V
SYNC Positive Input Hysteresis (Note 7) 0.2 V

SYNC Input Negative Threshold ● –1.8 –1.4 –1.0 V
SYNC Negative Input Hysteresis (Note 7) 0.2 V

Driver Pull-Up Resistance I

Driver Pull-Down Resistance I

Driver Peak Output Current (Note 7) 2 A

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UUW

PACKAGE/ORDER I FOR ATIO

ORDER PART

12V

15mA

T

= 125°C, θJA = 130°C/W

JMAX

Consult LTC Marketing for parts specified with wider operating temperature ranges.

The ●

denotes specifications which apply over the full operating

= 0V ● 0.5 1 mA

SYNC

f

= 100kHz, CME = CMF = 4700pF (Note 4) ● 715 mA

SYNC

= 0V ● –6 –10 µA

TMR

= 1000pF, R

TMR

= 1000pF, R

TMR

(Note 6)

= ±10V ● ±1 ±10 µA

SYNC

= –100mA 0.9 1.2 Ω

OUT

= 100mA 0.8 1.2 Ω

OUT

= 4.7k ● 40 120 ns

TMR

= 4.7k 2.5 V

TMR

● 318mV

● 1.6

● 1.6

NUMBER

LTC3901EGN

GN PART

MARKING

3901

3901f

LTC3901

ELECTRICAL CHARACTERISTICS

temperature range.

V

= 5V, TA = 25°C unless otherwise specified. (Note 3)

CC

The ●

denotes specifications which apply over the full operating

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Switching Characteristics (Note 8)

t

d

tr, t

f

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The LTC3901E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design; characterization and correlation
with statistical process controls.

Note 3: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.

Note 4: Supply current in normal operation is dominated by the current
needed to charge and discharge the external MOSFET gates. This current

SYNC Input to Driver Output Delay CME = CMF = 4700pF, V

Driver Rise/Fall Time CME = CMF = 4700pF, V

will vary with supply voltage, switching frequency and the external
MOSFETs used.

Note 5: Both CSE
the same performance specifications.

Note 6: The current sense comparator threshold has a 0.33%/°C
temperature coefficient (TC) to match the TC of the external MOSFET
R

DSON

Note 7: Guaranteed by design, not subject to test.
Note 8: Rise and fall times are measured using 10% and 90% levels. Delay

times are measured from ±1.4V at SYNC input to 20%/80% levels at the
driver output.

= ±5V ● 60 120 ns

SYNC

= ±5V 15 ns

SYNC

+

, CSE– and CSF+, CSF– current sense comparators have

.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Timeout vs V

5.25

TA = 25°C

5.20

R

TMR

C

TMR

5.15

5.10

5.05

5.00

4.95

TIMEOUT (µs)

4.90

4.85

4.80

4.75

4

5

= 51k
= 470pF

CC

8

7

6

VCC (V)

Current Sense Threshold vs
Temperature

18

VCC = 5V, 11V

17
16
15
14
13
12
11
10

9
8
7
6
5

CURRENT SENSE THRESHOLD (mV)

4
3

–50 100

050–25 25 75 125

TEMPERATURE (°C)

Timeout vs Temperature

5.25

VCC = 5V

5.20

5.15

5.10

5.05

5.00

4.95

TIMEOUT (µs)

4.90

4.85

4.80

10

11

3901 G01

9

4.75

= 51k

R

TMR

= 470pF

C

TMR

–50 0

–25

V

CS(MAX)

50

25

TEMPERATURE (°C)

75

100

Clamp Voltage vs CS

125

3901 G02

+

Input Current

18

TA = 25°C

17

16

15

14

CLAMP VOLTAGE (V)

13

12

CS(MAX)

V

11

3901 G04

10

05

10 2015

+

CS

INPUT CURRENT (mA)

25

30

3901 G05

Timeout vs R

10

TA = 25°C

9

= 5V

V

CC

= 470pF

C

TMR

8

7

6

5

4

TIMEOUT (µs)

3

2

1

0

0 10203040506070 8090100

TMR

R

TMR

(kΩ)

SYNC Positive Threshold vs
Temperature

1.8

1.7

1.6

1.5

1.4

1.3

1.2

SYNC POSITIVE THRESHOLD (V)

1.1

1.0
–25 25 75 125

–50

VCC = 11V

VCC = 5V

050

TEMPERATURE (°C)

3901 G03

100

3901 G06

3901f

3

LTC3901

UW

TYPICAL PERFOR A CE CHARACTERISTICS

SYNC Negative Threshold vs
Temperature Propagation Delay vs V

–1.0

VCC = 5V, 11V

–1.1

–1.2

–1.3

–1.4

–1.5

–1.6

SYNC NEGATIVE THRESHOLD (V)

–1.7

–1.8

–50

Propagation Delay vs C

120

TA = 25°C
V

110

100

90

80

70

SYNC TO ME

60

PROPAGATION DELAY (µs)

50

40

123 10

050

–25 25 75 125

TEMPERATURE (°C)

LOAD

= 5V

CC

SYNC TO MF

4567 98

C

(nF)

LOAD

100

3901 G07

3901 G10

120

TA = 25°C

= 4.7nF

C

110

LOAD

100

90

80

70

60

PROPAGATION DELAY (µs)

50

40

4

SYNC TO MF

57911

68

Rise/Fall Time vs V

50

TA = 25°C

45

40

35

30

25

20

15

RISE/FALL TIME (ns)

10

= 4.7nF

C

LOAD

FALL TIME

5

0

410

6857911

Rise/Fall Time vs Load
Capacitance

50

TA = 25°C

45

= 5V

V

CC

40

35

30

25

20

15

RISE/FALL TIME (ns)

10

5

0

RISE TIME

FALL TIME

1023 104567 98

C

(nF)

LOAD

V

V

(V)

CC

(V)

CC

CC

SYNC TO ME

10

3901 G08

CC

RISE TIME

3901 G11

Undervoltage Lockout Threshold
Voltage vs Temperature

4.5

4.4

4.3

4.2

4.1

4.0

3.9

3.8

3.7

3.6

VOLTAGE (V)

3.5

3.4

3.3

3.2

UNDERVOLTAGE LOCKOUT THRESHOLD

3.1

3.0
–50 100

RISING EDGE

FALLING EDGE

Propagation Delay vs
Temperature

120

VCC = 5V

= 4.7nF

C

110

LOAD

100

90

80

70

SYNC TO ME

60

PROPAGATION DELAY (µs)

50

40

–50 100

050–25 25 75 125

TEMPERATURE (°C)

Rise/Fall Time vs Temperature

50

VCC = 5V

45

40

35

30

25

20

15

RISE/FALL TIME (ns)

10

5

0

050–25 25 75 125

TEMPERATURE (°C)

= 4.7nF

C

LOAD

RISE TIME

–50 100

050–25 25 75 125

TEMPERATURE (°C)

3901 G143901 G13

SYNC TO MF

3901 G09

FALL TIME

3901 G12

4

3901f

UW

TYPICAL PERFOR A CE CHARACTERISTICS

V

Supply Current vs

CC

Temperature

20

C

= 4.7nF

LOAD

18

16

14

12

10

SUPPLY CURRENT (mA)

8

CC

V

6

4

–50 100

VCC = 11V

VCC = 5V

050–25 25 75 125
TEMPERATURE (°C)

3901 G15

30

25

20

15

10

SUPPLY CURRENT (mA)

V

Supply Current

CC

vs Load Capacitance

TA = 25°C

5

0

1023 104567 98

C

LOAD

LTC3901

VCC = 11V

VCC = 5V

(nF)

3901 G16

U

UU

PI FU CTIO S

P

VCC (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
R

to R

CSE1

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 sec­tion for more details on programming the timeout period.

CSE3

.

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
R

CSF1

to R

CSF3

.

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.

3901f

5