ANALOG DEVICES LT 8610 EMSE Datasheet

42V, 2.5A Synchronous

8610 TA01a

OUT

V

5.5V TO 42V

SW

Step-Down Regulator

with 2.5µA Quiescent

FEATURES DESCRIPTION

n

Wide Input Voltage Range: 3.4V to 42V

n

Ultralow Quiescent Current Burst Mode® Operation:

2.5μA I
Output Ripple < 10mV

n

High Efficiency Synchronous Operation:
96% Efficiency at 1A, 5V
94% Efficiency at 1A, 3.3V

n

Fast Minimum Switch-On Time: 50ns

n

Low Dropout Under All Conditions: 200mV at 1A

n

Allows Use Of Small Inductors

n

Low EMI

n

Adjustable and Synchronizable: 200kHz to 2.2MHz

n

Current Mode Operation

n

Accurate 1V Enable Pin Threshold

n

Internal Compensation

n

Output Soft-Start and Tracking

n

Small Thermally Enhanced 16-Lead MSOP Package

Regulating 12VIN to 3.3V

Q

P-P

from 12VIN

OUT

from 12VIN

OUT

OUT

APPLICATIONS

n

Automotive and Industrial Supplies

n

General Purpose Step-Down

n

GSM Power Supplies

The LT®8610 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 2.5µA of quiescent current. To p and
bottom power switches are included with all necessary
circuitry to minimize the need for external components.
Low ripple Burst Mode operation enables high efficiency
down to very low output currents while keeping the output
ripple below 10mV

P-P

to an external clock. Internal compensation with peak cur­rent mode
results

topology allows the use of small inductors and

in fast transient response and good loop stability.
The EN/UV pin has an accurate 1V threshold and can be
used to program V

undervoltage lockout or to shut down

IN

the LT8610 reducing the input supply current to 1µA. A
capacitor on the TR/SS pin programs the output voltage
ramp rate during start-up. The PG flag signals when V
is within ±9% of the programmed output voltage as well
as fault conditions. The LT8610 is available in a small
16-lead MSOP package with exposed pad for low thermal
resistance.

L, LT , LTC , LTM , Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.

LT8610

Current

. A SYNC pin allows synchronization

OUT

TYPICAL APPLICATION

5V 2.5A Step-Down Converter 12VIN to 5V

IN

4.7µF

10nF

1µF

f

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

60.4k

= 700kHz

CC

LT8610

PGND

BSTV

SW

BIAS

FB

GND

0.1µF

4.7µH

1M

10pF

243k

For more information www.linear.com/LT8610

47µF

V
5V

2.5A

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0

0.5

1

LOAD CURRENT (A)

Efficiency

OUT

1.5

fSW = 700kHz

VIN = 12V

= 24V

V

IN

2

8610 G01

2.5

8610fa

1

LT8610

EN/UV

CC

TOP VIEW

16-LEAD PLASTIC MSOP

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

(Note 1)

VIN, EN/UV, PG ..........................................................42V

BIAS .......................................................................... 30V

BST Pin Above SW Pin................................................4V

FB, TR/SS, RT, INTV

. ..............................................4V

CC

SYNC Voltage . ............................................................ 6V

Operating Junction Temperature Range (Note 2)

LT8610E ................................................. –40 to 125°C

LT8610I .................................................. –40 to 125°C

EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB

SYNC

TR/SS

V

V
PGND
PGND

RT

IN
IN

θ

JA

1
2
3
4
5
6
7
8

MSE PACKAGE

= 40°C/W, θ

17

GND

JC(PAD)

16
15
14
13
12
11
10
9

= 10°C/W

FB
PG
BIAS
INTV
BST
SW
SW
SW

LT8610H ................................................–40 to 150°C

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

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT8610EMSE#PBF LT8610EMSE#TRPBF 8610 16-Lead Plastic MSOP –40°C to 125°C

LT8610IMSE#PBF LT8610IMSE#TRPBF 8610 16-Lead Plastic MSOP –40°C to 125°C

LT8610HMSE#PBF LT8610HMSE#TRPBF 8610 16-Lead Plastic MSOP –40°C to 150°C

Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LT C Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage

Quiescent Current V

V

IN

Current in Regulation V

V

IN

Feedback Reference V

Feedback V

oltage Line Regulation V

oltage V

Feedback Pin Input Current V

Voltage I

INTV

CC

Undervoltage Lockout 2.5 2.6 2.7 V

INTV

CC

BIAS Pin Current Consumption V

Minimum On-Time I

Minimum Off-T

ime 50 80 110 ns

= 0V, V

EN/UV

= 2V, Not Switching, V

V

EN/UV

= 2V, Not Switching, V

V

EN/UV

= 0.97V, VIN = 6V, Output Load = 100µA

OUT

V

= 0.97V, VIN = 6V, Output Load = 1mA

OUT

= 6V, I

IN

V

= 6V, I

IN

= 4.0V to 42V, I

IN

= 1V –20 20 nA

FB

= 0mA, V

LOAD

I

= 0mA, V

LOAD

= 3.3V, I

BIAS

= 1A, SYNC = 0V

LOAD

I

= 1A, SYNC = 3.3V

LOAD

= 0V

SYNC

= 0V

SYNC

= 2V 0.24 0.5 mA

SYNC

= 0.5A

LOAD

= 0.5A

LOAD

= 0.5A

LOAD

= 0V

BIAS

= 3.3V

BIAS

= 1A, 2MHz 8.5 mA

LOAD

l

l

l

l
l

l

l

l
l

0.964

0.958

3.23

3.25

30
30

2.9 3.4 V

1.0

1.0

1.7

1.7

24

210

0.970

0.970

3
8

4

10

50

350

0.976

0.982

µA
µA

µA
µA

µA
µA

0.004 0.02 %/V

3.4

3.29

50
45

3.57

3.35

70
65

ns
ns

8610fa

V
V

V
V

2

For more information www.linear.com/LT8610

LT8610

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Oscillator Frequency R

Top Power NMOS On-Resistance

= 221k, I

T

R

= 60.4k, I

T

R

= 18.2k, I

T

= 1A 120 mΩ

I

SW

LOAD

LOAD
LOAD

= 1A

= 1A
= 1A

Top Power NMOS Current Limit

Bottom Power NMOS On-Resistance V

Bottom Power NMOS Current Limit V

SW Leakage Current V

= 3.4V, I

INTVCC

= 3.4V 2.5 3.3 4.8 A

INTVCC

= 42V, VSW = 0V, 42V –1.5 1.5 µA

IN

= 1A 65 mΩ

SW

EN/UV Pin Threshold EN/UV Rising

EN/UV Pin Hysteresis 40 mV

EN/UV Pin Current V

PG Upper Threshold Offset from V

PG Lower Threshold Offset from V

FB

FB

= 2V –20 20 nA

EN/UV

VFB Falling

VFB Rising

PG Hysteresis 1.3 %

PG Leakage V

PG Pull-Down Resistance V

= 3.3V –40 40 nA

PG

= 0.1V

PG

SYNC Threshold SYNC Falling

SYNC Rising

SYNC Pin Current V

= 2V –40 40 nA

SYNC

TR/SS Source Current

TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V 230 Ω

l

180

l

665

l

1.85

l

3.5 4.8 5.8 A

l

0.94 1.0 1.06 V

l

l

l

6 9.0 12 %

–6 –9.0 –12 %

0.8

1.6

l

1.2 2.2 3.2 µA

210
700

2.00

240
735

2.15

680 2000 Ω

1.1

2.0

1.4

2.4

kHz
kHz

MHz

V
V

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: The LT8610E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls. The
LT8610I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT8610H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction

temperatures greater than 125°C.
Note 3: This IC includes overtemperature protection that is intended to

protect the device during overload conditions. Junction temperature will

exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
will reduce lifetime.

For more information www.linear.com/LT8610

8610fa

3

LT8610

8610 G03

8610 G04

TYPICAL PERFORMANCE CHARACTERISTICS

Efficiency at 5V

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.5

0

Efficiency at 3.3V

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.001 10 100 1000 10000

0.01 0.1 1

OUT

1.5

1

LOAD CURRENT (A)

OUT

LOAD CURRENT (mA)

fSW = 700kHz

fSW = 700kHz

VIN = 12V
V

IN

VIN = 12V

= 24V

V

IN

2

8610 G01

= 24V

2.5

Efficiency at 3.3V

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.5

0

OUT

1.5

1

LOAD CURRENT (A)

fSW = 700kHz

VIN = 12V

= 24V

V

IN

2

8610 G02

2.5

Efficiency at 5V

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.01

0.001 0.1 1 10 100 1000

Efficiency vs Frequency Reference Voltage

96

V

OUT

94

92

90

88

EFFICIENCY (%)

86

84

82

0.25

= 3.3V

VIN = 12V

= 24V

V

IN

0.75 1.25 2.25

SWITCHING FREQUENCY (MHz)

1.75

8610 G05

0.985

0.982

0.979

0.976

0.973

0.970

0.967

0.964

REFERENCE VOLTAGE (V)

0.961

0.958

0.955
–55

–25

OUT

LOAD CURRENT (mA)

65

35

5
TEMPERATURE (°C)

fSW = 700kHz

VIN = 12V

= 24V

V

IN

95 125

10000

155

8610 G06

EN Pin Thresholds Load Regulation Line Regulation

1.04

1.03

1.02

1.01

1.00

0.99

0.98

EN THRESHOLD (V)

0.97

0.96

0.95
–55

4

5

–25

TEMPERATURE (°C)

EN RISING

EN FALLING

35 155

65

95 125

8610 G07

0.25
V

= 3.3V

OUT

0.20

0.15

0.10

(%)

0.05

OUT

–0.05

–0.10

CHANGE IN V

–0.15

–0.20

–0.25

= 12V

V

IN

0

0.5

0

1.5 2

1

LOAD CURRENT (A)

2.5

For more information www.linear.com/LT8610

3

8610 G08

0.10

0.08

0.06

0.04

(%)

0.02

OUT

0

–0.02

–0.04

CHANGE IN V

–0.06

–0.08

–0.10

V

= 3.3V

OUT

= 0.5A

I

LOAD

105

0

INPUT VOLTAGE (V)

2015

30 35 45

25

40

8610 G09

8610fa

TYPICAL PERFORMANCE CHARACTERISTICS

8610 G13

8610 G14

LT8610

No Load Supply Current No Load Supply Current

5.0
V

= 3.3V

OUT

4.5

IN REGULATION

4.0

3.5

3.0

2.5

2.0

1.5

INPUT CURRENT (µA)

1.0

0.5

0

5 15

10

0

25 45

20

INPUT VOLTAGE (V)

30

35

40

8610 G10

25

V

= 3.3V

OUT

= 12V

V

IN

IN REGULATION

20

15

10

INPUT CURRENT (µA)

5

0

–55 –25

5

35

TEMPERATURE (°C)

Top FET Current Limit Bottom FET Current Limit

5.0

4.5

4.0

3.5

CURRENT LIMIT (A)

3.0

30% DC

70% DC

3.6

3.4

3.2

3.0

2.8

CURRENT LIMIT (A)

2.6

Top FET Current Limit vs Duty Cycle

6.0

5.5

5.0

4.5

4.0

3.5

CURRENT LIMIT (A)

3.0

2.5

65

95

125

155

8610 G11

2.0

0.2 0.4 0.8

0

DUTY CYCLE

0.6

1.0

Switch Drop

250

SWITCH CURRENT = 1A

200

150

100

SWITCH DROP (mV)

50

TOP SW

BOT SW

2.5

–55

–25

450

400

350

300

250

200

150

SWITCH DROP (mV)

100

50

0

0

0.5

5 35 65

TEMPERATURE (°C)

TOP SW

BOT SW

1

1.5 3

SWITCH CURRENT (A)

2

95 125

2.5

8610 G41

2.4
–55

–25

TEMPERATURE (°C)

Minimum On-TimeSwitch Drop

80

75

70

65

60

55

50

45

MINIMUM ON-TIME (ns)

40

35

30

–55

I

LOAD

I

LOAD

I

LOAD

I

LOAD

5

–25

TEMPERATURE (°C)

= 1A, V
= 1A, V
= 2.5A, V
= 2.5A, V

5 35 65

= 0V

SYNC

= 3V

SYNC

= 0V

SYNC

= 3V

SYNC

65

35

95 125

95 125

8610 G15

8610 G17

155

0

–55 –25

5

TEMPERATURE (°C)

Minimum Off-Time

100

VIN = 3.3V

= 0.5A

I

LOAD

95

90

85

80

75

MINIMUM OFF-TIME (ns)

70

65

60

–25 5 65

–50

TEMPERATURE (°C)

65

35

35

95

95 125 155

125

155

8610 G40

8610 G18

8610fa

For more information www.linear.com/LT8610

5

LT8610

8610 G20

8610 G23

8610 G24

8610 G25

8610 G26

TYPICAL PERFORMANCE CHARACTERISTICS

Dropout Voltage Switching Frequency

800

700

600

500

400

300

200

DROPOUT VOLTAGE (mV)

100

0

0

1 2

0.5
LOAD CURRENT (A)

1.5 2.5

3

8610 G19

740

RT = 60.4k

730

720

710

700

690

680

SWITCHING FREQUENCY (kHz)

670

660

–25 5 65

–55

35

TEMPERATURE (°C)

95 125 155

Burst Frequency

800

VIN = 12V

= 3.3V

V

OUT

700

600

500

400

300

200

SWITCHING FREQUENCY (kHz)

100

0

0

Minimum Load to Full Frequency
(SYNC DC High) Soft-Start Tracking

100

V

= 5V

OUT

= 700kHz

f

SW

80

60

40

LOAD CURRENT (mA)

20

0

5 10

20

15 25 40 45

INPUT VOLTAGE (V)

30 35

8610 G39

Frequency Foldback

800

V

= 3.3V

OUT

= 12V

V

IN

700

600

500

400

300

200

SWITCHING FREQUENCY (kHz)

100

= 0V

V

SYNC

= 60.4k

R

T

0

0.2 0.4 0.8

0

FB VOLTAGE (V)

0.6

8610 G22

1

1.2

1.0

0.8

0.6

FB VOLTAGE (V)

0.4

0.2

0

0

0.2 0.4

50

100

LOAD CURRENT (mA)

0.8 1.2 1.4

0.6 1.0

TR/SS VOLTAGE (V)

150

200

8610 G21

Soft-Start Current

2.4
VSS = 0.5V

2.3

2.2

2.1

2.0

1.9

SS PIN CURRENT (µA)

1.8

1.7

1.6

–25 5 65

–50

6

35

TEMPERATURE (°C)

95 125 155

PG High Thresholds PG Low Thresholds

12.0

11.5

(%)

11.0

REF

10.5

10.0

9.5

9.0

8.5

8.0

7.5

PG THRESHOLD OFFSET FROM V

7.0
–55

–25

FB RISING

FB FALLING

65

35

5

TEMPERATURE (°C)

95 125

For more information www.linear.com/LT8610

155

–7.0

–7.5

(%)

–8.0

REF

–8.5

–9.0

–9.5

–10.0

–10.5

–11.0

–11.5

PG THRESHOLD OFFSET FROM V

–12.0

–55

–25

FB RISING

FB FALLING

65

35

5
TEMPERATURE (°C)

95 125

155

8610fa

TYPICAL PERFORMANCE CHARACTERISTICS

RT Programmed Switching
Frequency

250

225

200

175

150

125

100

75

RT PIN RESISTOR (kΩ)

50

25

0

0.6

0.2
SWITCHING FREQUENCY (MHz)

1.4

1.8

1

2.2

8610 G27

VIN UVLO Bias Pin Current

3.6

3.4

3.2

3.0

2.8

2.6

INPUT VOLTAGE (V)

2.4

2.2

2.0
–25 5 65

–55

35

TEMPERATURE (°C)

95 125 155

8610 G28

5.00
V

= 5V

BIAS

= 5V

V

OUT

4.75

4.50

4.25

4.00

3.75

BIAS PIN CURRENT (mA)

3.50

3.25

3.00

5

I

LOAD

= 700kHz

f

SW

10

= 1A

15

INPUT VOLTAGE (V)

LT8610

25

30

20

35

40

45

8610 G29

Bias Pin Current

12

V

= 5V

BIAS

= 5V

V

OUT

10

= 12V

V

IN

= 1A

I

LOAD

8

6

4

BIAS PIN CURRENT (mA)

2

0

0

0.5 1 1.5 2
SWITCHING FREQUENCY (MHz)

Switching Waveforms

I

L

1A/DIV

V

SW

10V/DIV

36V

TO 5V

IN

OUT

500ns/DIV

AT 1A

8610 G30

8610 G33

2.5

1A/DIV

V

SW

5V/DIV

I

LOAD

1A/DIV

V

OUT

100mV/DIV

Switching Waveforms Switching Waveforms

I

L

8610 G31

12V

IN

TO 5V

OUT

500ns/DIV

AT 1A

200mA/DIV

V

SW

5V/DIV

I

L

12V
V

SYNC

IN

TO 5V

= 0V

OUT

500µs/DIV

AT 10mA

Transient Response Transient Response

I

LOAD

1A/DIV

V

OUT

200mV/DIV

0.5A TO 1.5A TRANSIENT
, 5V

12V

IN

C

= 47µF

OUT

50µs/DIV

OUT

8610 G34

0.5A TO 2.5A TRANSIENT
12V

, 5V

IN

C

= 47µF

OUT

50µs/DIV

OUT

8610 G32

8610 G35

For more information www.linear.com/LT8610

8610fa

7

LT8610

TYPICAL PERFORMANCE CHARACTERISTICS

Start-Up Dropout Performance Start-Up Dropout Performance

V

IN

2V/DIV

V

OUT

2V/DIV

2.5Ω LOAD
(2A IN REGULATION)

I

LOAD

1A/DIV

V

OUT

200mV/DIV

Transient Response

50mA TO 1A TRANSIENT
12V

, 5V

IN

C

= 47µF

OUT

50µs/DIV

OUT

8610 G36

PIN FUNCTIONS

SYNC (Pin 1): External Clock Synchronization Input.
Ground this pin for low ripple Burst Mode operation at low
output loads. Tie to a clock source for synchronization to
an external frequency. Apply a DC voltage of 3V or higher
or tie to INTV
skipping mode, the I
Do not float this pin.

TR/SS (Pin 2): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate during
start-up. A TR/SS voltage below 0.97V forces the LT8610
to regulate the FB pin to equal the TR/SS pin voltage. When
TR/SS is above 0.97V, the tracking function is disabled
and the internal reference resumes control of the error
amplifier. An internal 2.2μA pull-up current from INTV
on this pin allows a capacitor to program output voltage
slew rate. This pin is pulled to ground with an internal 230Ω
MOSFET during shutdown and fault conditions; use a series
resistor if driving from a low impedance output. This pin
may be left floating if the tracking function is not

RT (Pin

3): A resistor is tied between RT and ground to

set the switching frequency.

EN/UV (Pin 4): The LT8610 is shut down when this pin
is low and active when this pin is high. The hysteretic
threshold voltage is 1.00V going up and 0.96V going
down. Tie to V
external resistor divider from V

threshold below which the LT8610 will shut down.

a V

IN

for pulse-skipping mode. When in pulse-

CC

will increase to several hundred µA.

Q

needed.

if the shutdown feature is not used. An

IN

can be used to program

IN

CC

V

IN

V

OUT

100ms/DIV

(Pins 5, 6): The VIN pins supply current to the LT8610

V

IN

8610 G37

V

IN

2V/DIV

V

OUT

2V/DIV

20Ω LOAD
(250mA IN REGULATION)

V

OUT

100ms/DIV

V

IN

internal circuitry and to the internal topside power switch.
These pins must be tied together and be locally bypassed.
Be sure to place the positive terminal of the input capaci
tor as close as possible to the V

pins, and the negative

IN

capacitor terminal as close as possible to the PGND pins.

PGND (Pins 7, 8): Power Switch Ground. These pins are
the return path of the internal bottom-side power switch
and must be tied together. Place the negative terminal of

the input capacitor as close to the PGND pins as possible.

SW (Pins 9, 10, 11): The SW pins are the outputs of the

internal power switches.

them to the inductor and boost capacitor. This node

nect

should be kept small on the PCB for good per

Tie these pins together and con-

formance.

BST (Pin 12): This pin is used to provide a drive voltage,

higher than the input voltage, to the topside power switch.

Place a 0.1µF boost capacitor as close as possible to the IC.

INTV

(Pin 13): Internal 3.4V Regulator Bypass Pin.

CC

The internal power drivers and control circuits are pow-

ered from
rent is 20
circuitry. INTV
V

BIAS

Voltage on INTV

V

BIAS

this voltage. INTV

mA. Do not load the INTVCC pin with external

current will be supplied from BIAS if

CC

> 3.1V, otherwise current will be drawn from VIN.

will vary between 2.8V and 3.4V when

CC

is between 3.0V and 3.6V. Decouple this pin to power

maximum output cur-

CC

ground with at least a 1μF low ESR ceramic capacitor
placed close to the IC.

8610 G38

-

8

8610fa

For more information www.linear.com/LT8610

PIN FUNCTIONS

OUT

V

LT8610

BIAS (Pin 14): The internal regulator will draw current from
BIAS instead of V

when BIAS is tied to a voltage higher

IN

than 3.1V. For output voltages of 3.3V and above this pin
should be tied to V
than V

use a 1µF local bypass capacitor on this pin.

OUT

. If this pin is tied to a supply other

OUT

PG (Pin 15): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within ±9% of the final regulation voltage, and there are
no fault conditions. PG is valid when V

is above 3.4V,

IN

FB (Pin 16): The LT8610 regulates the FB pin to 0.970V.
Connect the

connect

feedback resistor divider tap to this pin. Also,

a phase lead capacitor between FB and V

OUT

Typically, this capacitor is 4.7pF to 10pF.

GND (Exposed Pad Pin 17): Ground. The exposed pad
must be connected to the negative terminal of the input
capacitor and soldered to the PCB in order to lower the
thermal resistance.

.

regardless of EN/UV pin state.

BLOCK DIAGRAM

V

OUT

IN

5, 6

C

IN

1V

EN/UV

4

PG

15

R1C1

FB

16

TR/SS

2

RT

3

SYNC

1

INTERNAL 0.97V REF

+

SHDN

–

±9%

SHDN
TSD
INTV

UVLO

CC

V

UVLO

IN

2.2µA

ERROR

AMP

+
+
–

–
+

SLOPE COMP

OSCILLATOR

200kHz TO 2.2MHz

V

C

SHDN
TSD
V

UVLO

IN

GND

17

BURST

DETECT

SWITCH

LOGIC

AND

ANTI-

SHOOT

THROUGH

3.4V
REG

M1

M2

INTV

PGND

BIAS

BST

SW

9-11

7, 8

14

CC

13

12

8610 BD

C

VCC

C

BST

L

C

OUT

V

IN

R3
OPT

R4
OPT

V

R2

C
OPT

R

SS

T

For more information www.linear.com/LT8610

8610fa

9

LT8610

OPERATION

The LT8610 is a monolithic, constant frequency, current
mode step-down DC/DC converter. An oscillator, with
frequency set using a resistor on the RT pin, turns on
the internal top power switch at the beginning of each
clock cycle. Current in the inductor then increases until
the top switch current comparator trips and turns off the
top power switch. The peak inductor current at which
the top switch turns off is controlled by the voltage on
the internal VC node. The error amplifier servos the VC
node by comparing the voltage on the V
internal 0.97V reference. When the load current increases
it causes a reduction in the feedback voltage relative to
the reference leading the error amplifier to raise the VC
voltage until the average inductor current matches the new
load current. When the top power switch turns off, the
synchronous power switch turns on until the next clock
cycle begins or inductor current falls to zero. If overload
conditions result in more than 3.3A flowing through the
bottom switch, the next clock cycle will be delayed until
switch current returns to a safe level.

If the EN/UV pin is low, the LT
draws

1µA from the input. When the EN/UV pin is above

1V, the switching regulator will become active.

To optimize efficiency at light loads, the LT8610 operates
in Burst Mode operation in light load situations. Between
bursts, all circuitry associated with controlling the output
switch is shut down, reducing the input supply current to

1.7μA. In a typical application, 2.5μA will be consumed

8610 is shut down and

pin with an

FB

from the input supply when regulating with no load. The
SYNC pin is tied low to use Burst Mode operation and can
be tied to a logic high to use pulse-skipping mode. If a
clock is applied to the SYNC pin the part will synchronize to
an external clock frequency and operate in pulse-skipping
mode. While in pulse-skipping mode the oscillator operates
continuously and positive SW transitions are aligned to
the clock. During light loads, switch pulses are skipped
to regulate the output and the quiescent current will be
several hundred µA.

To improve efficiency across all loads, supply current to
internal circuitry can be sourced from the BIAS pin when
biased at 3.3V or above. Else, the internal circuitry will draw
current from V

if the LT8610 output is programmed at 3.3V or above.

V

OUT

Comparators monitoring the FB pin voltage will pull the

PG pin low if the output voltage varies more than ±9%

(typical) from the set point, or if a fault condition is present.

The oscillator reduces the LT8610’s operating frequency

when the voltage at the FB pin is low. This frequency

foldback helps to control the inductor current when the
output voltage is lower than the programmed value which
occurs during start-up or overcurrent conditions. When
a clock is applied to the SYNC pin or the SYNC pin is
held DC high, the frequency foldback is disabled and the
switching frequency will slow down only during overcur

rent conditions.

. The BIAS pin should be connected to

IN

-

10

8610fa

For more information www.linear.com/LT8610

APPLICATIONS INFORMATION

LT8610

Achieving Ultralow Quiescent Current

To enhance efficiency at light loads, the LT8610 operates
in low ripple Burst Mode operation, which keeps the out

­put capacitor charged to the desired output voltage while
minimizing the input quiescent current and minimizing
output voltage ripple. In Burst Mode operation the LT8610
delivers single small pulses of current to the output capaci

­tor followed by sleep periods where the output power is
supplied

by the output capacitor. While in sleep mode the

LT8610 consumes 1.7μA.

As the output load decreases, the frequency of single cur

­rent pulses decreases (see Figure 1a) and the percentage

time the LT8610 is in sleep mode increases, resulting in

of

Burst Frequency

800

VIN = 12V

= 3.3V

V

OUT

700

600

500

400

300

200

SWITCHING FREQUENCY (kHz)

100

0

0

50

Minimum Load to Full Frequency (SYNC DC High)

100

5V

OUT

700kHz

80

60

100

LOAD CURRENT (mA)

(1a)

150

200

8610 F01a

much higher light load efficiency than for typical convert­ers. By
q

maximizing the time between pulses, the converter

uiescent current approaches 2.5µA for a typical application

when there is no output load. Therefore, to optimize the

quiescent current performance at light loads, the current

in the feedback resistor divider must be minimized as it

appears to the output as load current.

While in Burst Mode operation the current limit of the top
switch is approximately 400mA resulting in output voltage
ripple shown in Figure 2. Increasing the

will decrease

the output ripple proportionally. As load ramps

output capacitance

upward from zero the switching frequency will increase

but only up to the switching frequency programmed by

the resistor at the RT pin as shown in Figure 1a. The out

put load
frequency

at which the LT8610 reaches the programmed

varies based on input voltage, output voltage,

-

and inductor choice.

For some applications it is desirable for the LT8610 to
operate in pulse-skipping mode, offering two major differ

ences from

Burst Mode operation. First is the clock stays

-

awake at all times and all switching cycles are aligned to
the

clock. In this mode much of the internal circuitry is
awake at all times, increasing quiescent current to several
hundred µA. Second is that full switching frequency is
reached at lower output load than in Burst Mode operation
(see Figure 1b). To enable pulse-skipping mode, the SYNC
pin is tied high either to a logic output or to the INTV

CC

pin. When a clock is applied to the SYNC pin the LT8610
will also operate in pulse-skipping mode.

I

L

200mA/DIV

40

LOAD CURRENT (mA)

20

0

5 10

20

15 25 40 45

INPUT VOLTAGE (V)

(1b)

30 35

8610 F01b

Figure 1. SW Frequency vs Load Information in
Burst Mode Operation (1a) and Pulse-Skipping Mode (1b)

For more information www.linear.com/LT8610

V

OUT

10mV/DIV

SYNC

= 0V

5µs/DIVV

Figure 2. Burst Mode Operation

8610 F02

8610fa

11

LT8610

V

46.5

V

+ V

( )

APPLICATIONS INFORMATION

FB Resistor Network

The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to:

R1= R2



OUT





0.970V

–1






(1)

Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.

If low input quiescent current and good light-load efficiency
are desired, use large resistor values for the FB resistor
divider. The current flowing in the divider acts as a load
current, and will increase the no-load input current to the
converter, which is approximately:

IQ= 1.7µA+

V



OUT





R1+ R2












V

OUT

V

IN



1















n



(2)

where 1.7µA is the quiescent current of the LT8610 and
the second term is the current in the feedback divider
reflected to the input of the buck operating at its light
load efficiency n. For a 3.3V application with R1 = 1M and
R2 = 412k, the feedback divider draws 2.3µA. With V

IN

=
12V and n = 80%, this adds 0.8µA to the 1.7µA quiescent
current resulting in 2.5µA no-load current from the 12V
supply. Note that this equation implies that the no-load
current is a function of V

; this is plotted in the Typical

IN

Performance Characteristics section.

When using large FB resistors, a 4.7pF to 10pF phase-lead
capacitor should be connected from V

OUT

to FB.

Setting the Switching Frequency

The LT8610 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary R

value for a desired switching

T

frequency is in Table 1.

where RT is in kΩ and fSW is the desired switching fre-

quency in MHz.

Table 1. SW Frequency vs RT Value

(MHz) RT (kΩ)

f

SW

0.2 232

0.3 150

0.4 110

0.5 88.7

0.6 71.5

0.7 60.4

0.8 52.3

1.0 41.2

1.2 33.2

14 28.0

1.6 23.7

1.8 20.5

2.0 18.2

2.2 15.8

Operating Frequency Selection and Trade-Offs

Selection of the operating frequency is a trade-off between
efficiency, component size, and input voltage range. The
advantage of high frequency operation is that smaller induc

-

tor and capacitor values may be used. The disadvantages

are lower efficiency and a smaller input voltage range.

highest switching frequency (f

The

SW(MAX)

) for a given

application can be calculated as follows:

f

SW(MAX)

where V

IN

voltage, V

=

t

ON(MIN)

OUT

VIN– V

is the typical input voltage, V

SW(TOP)

and V

SW(BOT)

SW(BOT)

SW( TOP)

+ V

SW(BOT)

is the output

OUT

are the internal switch

(4)

drops (~0.3V, ~0.15V, respectively at maximum load)

and t

ON(MIN)

is the minimum top switch on-time (see the
Electrical Characteristics). This equation shows that a
slower switching frequency is necessary to accommodate

a high V

IN/VOUT

ratio.

resistor required for a desired switching frequency

The R

T

can be calculated using:

For transient operation, V

lute maximum

rating of 42V regardless of the RT value,

may go as high as the abso-

IN

however the LT8610 will reduce switching frequency as

RT=

12

– 5.2

f

SW

(3)

For more information www.linear.com/LT8610

necessary to maintain control of inductor current to as
sure safe operation.

-

8610fa

APPLICATIONS INFORMATION

V

+ V

V

+ V

1

2

∆I

2

LT8610

The LT8610 is capable of a maximum duty cycle of greater
than 99%, and the V
R

of the top switch. In this mode the LT8610 skips

DS(ON)

-to-V

IN

dropout is limited by the

OUT

switch cycles, resulting in a lower switching frequency
than programmed by RT.

For applications that cannot allow deviation from the pro
grammed switching

frequency at low VIN/V

ratios use

OUT

-

the following formula to set switching frequency:

V

IN(MIN)

where V

OUT

=

1– fSW• t

IN(MIN)

skipped cycles, V
V

SW(BOT)

are the internal switch drops (~0.3V, ~0.15V,
respectively at maximum load), f
quency (set by RT),

SW(BOT)

OFF(MIN)

– V

SW(BOT)

+ V

SW( TOP)

(5)

is the minimum input voltage without

is the output voltage, V

OUT

is the switching fre-

SW

and t

OFF(MIN)

is the minimum switch

SW(TOP)

and

off-time. Note that higher switching frequency will increase
the minimum input voltage below which cycles will be
dropped to achieve higher duty cycle.

Inductor Selection and Maximum Output Current

where ∆I
Equation 9 and I

is the inductor ripple current as calculated in

L

LOAD(MAX)

is the maximum output load

for a given application.

As a quick example, an application requiring 1A output
should use an inductor with an RMS rating of greater than
1A and an I

of greater than 1.3A. During long duration

SAT

overload or short-circuit conditons, the inductor RMS
routing requirement is greater to avoid overheating of the

inductor. To keep the efficiency high, the series resistance
(DCR) should be less than 0.04Ω, and the core material
should be intended for high frequency applications.

The LT8610 limits the peak switch current in order to
protect the switches and the system from overload faults.
The top switch current limit (I

) is at least 3.5A at low

LIM

duty cycles and decreases linearly to 2.8A at DC = 0.8. The
inductor value must then be sufficient to supply the desired
maximum output current (I

OUT(MAX)

of the switch current limit (I

I

OUT(MAX)

= I

LIM

L

–

LIM

), which is a function

) and the ripple current.

(8)

The LT8610 is designed to minimize solution size by
allowing the inductor to be chosen based on the output
load requirements of the application. During overload or
short-circuit conditions the LT8610 safely tolerates opera

­tion with a saturated inductor through the use of a high
speed peak-current mode architecture.

A good first choice for the inductor value is:

OUT

L =

where f

SW

the output voltage, V

SW(BOT)

f

SW

is the switching frequency in MHz, V

SW(BOT)

is the bottom switch drop

OUT

(6)

is

(~0.15V) and L is the inductor value in μH.

To avoid overheating and poor efficiency, an inductor must
be chosen with an RMS current rating that is greater than
the maximum expected output load of the application. In
addition, the saturation current (typically labeled I

SAT

)
rating of the inductor must be higher than the load current
plus 1/2 of in inductor ripple current:

I

L(PEAK)

= I

LOAD(MAX )

+

∆I

L

(7)

The peak-to-peak ripple current in the inductor can be

calculated as follows:

∆IL=

where f

OUT

SW



• 1–




V

V

IN(MAX )

V

L • f

is the switching frequency of the LT8610, and

SW

OUT






(9)

L is the value of the inductor. Therefore, the maximum
output current that the LT8610 will deliver depends on
the switch current limit, the inductor value, and the input
and output voltages. The inductor value may have to be
increased if the inductor ripple current does not allow
sufficient maximum output current (I

OUT(MAX)

) given the
switching frequency, and maximum input voltage used in
the desired application.

The optimum inductor for a given application may differ

from the one indicated by this design guide. A larger value
inductor provides a higher maximum load current and
reduces the output voltage ripple. For applications requir

-

ing smaller load currents, the value of the inductor may

lower and the LT8610 may operate with higher ripple

be

8610fa

For more information www.linear.com/LT8610

13

LT8610

APPLICATIONS INFORMATION

current. This allows use of a physically smaller inductor,
or one with a lower DCR resulting in higher efficiency. Be
aware that low inductance may result in discontinuous
mode operation, which further reduces maximum load
current.

For more information about maximum output current
and discontinuous operation, see Linear Technology’s
Application Note 44.

Finally, for duty cycles greater than 50% (V
a minimum inductance is required to avoid sub-harmonic
oscillation. See Application Note 19.

Input Capacitor

Bypass the input of the LT8610 circuit with a ceramic ca
pacitor of
the
over temperature and applied voltage, and should not be
used. A 4.7μF to 10μF ceramic capacitor is adequate to
bypass the LT8610 and will easily handle the ripple current.
Note that larger input capacitance is required when a lower
switching frequency is used. If the input power source has
high impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.

Step-down regulators draw current from the
ply in
capacitor
ripple at the LT8610 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7μF capacitor is capable of this task, but only if it is
placed close to the LT8610 (see the PCB Layout section).
A second precaution regarding the ceramic input capacitor
concerns the maximum input voltage rating of the LT8610.
A ceramic input capacitor combined with trace or cable
inductance forms a high quality (under damped) tank cir
cuit. If the LT8610 circuit is plugged into a live supply, the
input
exceeding the LT8610’s voltage rating. This situation is
easily avoided (see Linear Technology Application Note 88).

X7R or X5R type placed as close as possible to

and PGND pins. Y5V types have poor performance

V

IN

pulses with very fast rise and fall times. The input

is required to reduce the resulting voltage

voltage can ring to twice its nominal value, possibly

OUT/VIN

> 0.5),

-

input sup-

-

Output Capacitor and Output Ripple

The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated
by the LT8610 to produce the DC output. In this role it
determines the output ripple, thus low impedance at the

switching frequency is important. The second function

is to store energy in order to satisfy transient loads
stabilize

have very low equivalent series resistance (ESR) and

provide the best ripple performance. For good starting

values, see the Typical Applications section.

Use X5R or X7R types. This choice will provide low output

ripple and good transient response. Transient performance
can be improved with a higher value output capacitor and
the addition of a feedforward capacitor placed between
V

OUT

decrease the output voltage ripple. A lower value of output

capacitor can be used to save space and cost but transient

performance will suffer and may cause loop instability. See
the Typical Applications in this data sheet for suggested
capacitor values.

When choosing a capacitor, special attention should be
given to the data sheet to calculate the effective capacitance
under the relevant operating conditions of voltage bias and
temperature. A physically larger capacitor or one with a
higher voltage rating may be required.

Ceramic Capacitors

Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT8610 due to their piezoelectric nature.
When in Burst Mode operation, the LT8610’s switching

frequency depends

loads the LT8610 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT8610
operates at a lower current limit during Burst Mode op
eration, the noise is typically very quiet to a casual ear. If

this

electrolytic capacitor at the output. Low noise ceramic
capacitors are also available.

the LT8610’s control loop. Ceramic capacitors

and FB. Increasing the output capacitance will also

on the load current, and at very light

is unacceptable, use a high performance tantalum or

and

-

14

8610fa

For more information www.linear.com/LT8610

APPLICATIONS INFORMATION

R3

LT8610

A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT8610. As

, a

previously mentioned

ceramic input capacitor combined
with trace or cable inductance forms a high quality (un­derdamped) tank

circuit. If the LT8610 circuit is plugged

into a live supply, the input voltage can ring to twice its

nominal value, possibly exceeding the LT8610’s rating.

This situation is easily avoided (see Linear Technology

Application Note 88).

Enable Pin

The LT8610 is in shutdown when the EN pin is low and

active when the pin is high. The rising threshold of the EN
comparator is 1.0V, with 40mV of hysteresis. The EN pin
can be tied to V

if the shutdown feature is not used, or

IN

tied to a logic level if shutdown control is required.

Adding a resistor divider from V

LT8610 to regulate the output only when V

to EN programs the

IN

is above a

IN

desired voltage (see the Block Diagram). Typically, this

threshold, V

, is used in situations where the input

IN(EN)

supply is current limited, or has a relatively high source

resistance. A switching regulator draws constant power

from the source, so source current increases

as source

voltage drops. This looks like a negative resistance load

to the source and can cause the source to current limit or

latch low under low source voltage conditions. The V

IN(EN)

threshold prevents the regulator from operating at source

voltages where the problems might occur. This threshold

can be adjusted by setting the values R3 and R4 such that

they satisfy the following equation:

V

IN(EN)



=





where the LT8610 will remain off until V

R4

+ 1



•1.0V





(10)

is above V

IN

IN(EN)

.
Due to the comparator’s hysteresis, switching will not stop
until the input falls slightly below V

IN(EN)

.

When operating in Burst Mode operation for light load
currents, the current through the V

resistor network

IN(EN)

can easily be greater than the supply current consumed
by the LT8610. Therefore, the V

resistors should be

IN(EN)

large to minimize their effect on efficiency at low loads.

INTV

Regulator

CC

An internal low dropout (LDO) regulator produces the 3.4V
supply from V

bias circuitry. The INTV

that powers the drivers and the internal

IN

can supply enough current for

CC

the LT8610’s circuitry and must be bypassed to ground
with a minimum of 1μF ceramic capacitor. Good bypassing
is necessary to supply the high transient currents required

by the power MOSFET gate drivers. To improve efficiency
the internal LDO can also draw current from the BIAS
pin when the BIAS pin is at 3.1V or higher. Typically the
BIAS pin can be tied to the output of the LT8610, or can
be tied to an external supply
connected

to a supply other than V

of 3.3V or above. If BIAS is

, be sure to bypass

OUT

with a local ceramic capacitor. If the BIAS pin is below

3.0V, the internal LDO will consume current from V

Applications with high input voltage and high switching
frequency where the internal LDO pulls current from V

will increase die temperature because of the higher power

dissipation across the LDO. Do not connect an external
load to the INTV

CC

pin.

Output Voltage Tracking and Soft-Start

T

he LT8610 allows the user to program its output voltage

ramp rate by means of the TR/SS pin. An internal 2.2μA

pulls up the TR/SS pin to INTV
capacitor on TR/SS enables soft starting the output to pre-

current surge

vent

on the input supply. During the soft-start

. Putting an external

CC

ramp the output voltage will proportionally track the TR/SS
pin voltage. For output tracking applications, TR/SS can

be externally driven by another voltage source. From 0V to

0.97V, the TR/SS voltage will override the internal 0.97V

reference input to the error amplifier, thus regulating the

FB pin voltage to that of TR/SS pin

. When TR/SS is above

0.97V, tracking is disabled and the feedback voltage will
regulate to the internal reference voltage. The TR/SS pin

may be left floating if the function is not needed.

An active pull-down circuit is connected to the TR/SS pin

which will discharge the external soft-start capacitor in

the case of fault conditions and restart the ramp when the

faults are cleared. Fault conditions that clear the soft-start

capacitor are the EN/UV pin transitioning low, V

IN

falling too low, or thermal shutdown.

IN

IN

voltage

.

For more information www.linear.com/LT8610

8610fa

15

LT8610

APPLICATIONS INFORMATION

Output Power Good

When the LT8610’s output voltage is within the ±9%
window of the regulation point, which is a V

voltage in

FB

the range of 0.883V to 1.057V (typical), the output voltage
is considered good and the open-drain PG pin goes high
impedance and is typically pulled high with an external
resistor. Otherwise, the internal pull-down device will pull
the PG pin low. To prevent glitching both the upper and
lower thresholds include 1.3% of hysteresis.

The PG pin is also actively pulled low during several fault
conditions: EN/UV pin is below 1V, INTV
low, V

is too low, or thermal shutdown.

IN

has fallen too

CC

Synchronization

To select low ripple Burst Mode operation, tie the SYNC pin
below 0.4V (this can be ground or a logic low output). To
synchronize the LT8610 oscillator to an external frequency
connect a square wave (with 20% to 80% duty cycle) to
the SYNC pin. The square wave amplitude should have val

-

leys that are below 0.4V and peaks above 2.4V (up to 6V).

LT8610 will not enter Burst Mode operation at low

The
output loads while synchronized to an external clock, but
instead will pulse skip to maintain regulation

. The LT8610

may be synchronized over a 200kHz to 2.2MHz range. The

resistor should be chosen to set the LT8610 switching

R

T

frequency equal to or below the lowest synchronization
input. For example, if the synchronization signal will be
500kHz and higher, the R
The slope compensation is set by the R

should be selected for 500kHz.

T

value, while the

T

minimum slope compensation required to avoid subhar­monic oscillations

is established by the inductor size,
input voltage, and output voltage. Since the synchroniza­tion frequency

will not change the slopes of the inductor
current waveform, if the inductor is large enough to avoid
subharmonic oscillations at the frequency set by R

, then

T

the slope compensation will be sufficient for all synchro­nization frequencies.

some applications it is desirable for the LT8610 to

For
operate in pulse-skipping mode, offering two major differ

­ences from Burst Mode operation. First is the clock stays
awake at all times and all switching cycles are aligned to
the clock. Second is that full switching frequency is reached
at lower output load than in Burst Mode operation. These

two differences come at the expense of increased quiescent

current. To enable pulse

-skipping mode,

the SYNC pin is

tied high either to a logic output or to the INTVCC pin.

The LT8610 does not operate in forced continuous mode

regardless of SYNC signal. Never leave the SYNC pin
floating.

Shorted and Reversed Input Protection

The LT8610 will tolerate a shorted output. Several features
are used for protection during output short-circuit and
brownout conditions. The first is the switching frequency

will be folded back while the output is lower than the set
point to maintain inductor current control. Second, the
bottom switch current is monitored such that if inductor
current is beyond safe levels switching of the top switch
will be delayed until such time as the inductor current
falls to safe levels.

Frequency foldback behavior depends on the state of the
SYNC pin: If the SYNC pin is low the switching frequency
will slow while the output voltage is lower than the pro

­grammed level. If the SYNC pin is connected to a clock
source or tied high, the LT8610 will stay at the programmed
frequency without foldback and only slow switching if the
inductor current exceeds safe levels.

There is another situation to consider in systems where
the output
is

absent. This may occur in battery charging applications

will be held high when the input to the LT8610

or in battery-backup systems where a battery or some
other supply is diode ORed with the LT8610’s output. If
the V

(either by a logic signal or because it is tied to V

pin is allowed to float and the EN pin is held high

IN

), then

IN

the LT8610’s internal circuitry will pull its quiescent current
through its SW pin. This is acceptable if the system can

tolerate several μA in this state. If the EN pin is grounded
the SW pin current will drop to near 1µA. However, if the

pin is grounded while the output is held high, regard-

V

IN

less of EN, parasitic body diodes inside the LT8610 can

current from the output through the SW pin and

pull
the V

pin. Figure 3 shows a connection of the VIN and

IN

EN/UV pins that will allow the LT8610 to run only when

input voltage is present and that protects against a

the
shorted or reversed input.

8610fa

16

For more information www.linear.com/LT8610

APPLICATIONS INFORMATION

V

D1

8610 F03

8610 F04

GROUND PLANE

V

IN

IN

LT8610

EN/UV

GND

SYNC

LT8610

GND

V

1

16

FB

OUT

Figure 3. Reverse VIN Protection

PCB Layout

For proper operation and minimum EMI, care must be taken
during printed circuit board layout. Figure 4 shows the
recommended component placement with trace, ground
plane and via locations. Note that large, switched currents
flow in the LT8610’s V
pacitor (C1). The loop

pins, PGND pins, and the input ca-

IN

formed by the input capacitor should
be as small as possible by placing the capacitor adjacent
to the V

and PGND pins. When using a physically large

IN

input capacitor the resulting loop may become too large
in which case using a small case/value capacitor placed
close to the V

and PGND pins plus a larger capacitor

IN

further away is preferred. These components, along with
the inductor and output capacitor, should be placed on the
same side of the circuit board, and their connections should
be made on that layer. Place a local, unbroken ground
plane under the application circuit on the layer closest to
the surface layer. The SW and BOOST nodes should be
as small as possible. Finally, keep the FB and RT nodes
small so that the ground traces will shield them from the
SW and BOOST nodes. The exposed pad on the bottom

of
the package must be soldered to ground so that the pad
is connected to ground electrically and also acts as a heat
sink thermally. To keep thermal resistance low, extend the
ground plane as much as possible, and add thermal vias
under and near the LT8610 to additional ground planes
within the circuit board and on the bottom side.

High Temperature Considerations

For higher ambient temperatures, care should be taken in
the layout of the PCB to ensure good heat sinking of the
LT8610. The exposed pad on the bottom of the package

TR/SS

2

RT

3

EN/UV

V

IN

GND

V

LINE TO BIAS VIAS TO GROUND PLANE

OUT

4

5

6

7

8

15 PG

BIAS

14

INTV

13

CC

BST

12

11

10

9

V

OUT

OUTLINE OF LOCAL

SW

Figure 4. Recommended PCB Layout for the LT8610

must be soldered to a ground plane. This ground should
be tied to large copper layers below with thermal vias;
these layers will spread heat dissipated by the LT8610.
Placing additional vias can reduce thermal resistance
further. The maximum load current should be derated
as the ambient temperature approaches the maximum
junction rating. Power dissipation within the LT8610 can
be estimated by calculating the total power loss from an
efficiency measurement and subtracting the inductor loss.
The die temperature is calculated by multiplying the LT8610
power dissipation by the thermal resistance from junction
to ambient. The LT8610 will stop switching and indicate

fault condition

a

if safe junction temperature is exceeded.

For more information www.linear.com/LT8610

8610fa

17

LT8610

8610 TA02

OUT

V

5.5V TO 42V

8610 TA03

OUT

V

5.5V TO 42V

8610 TA04

OUT

V

(42V TRANSIENT)

8610 TA05

OUT

V

3.8V TO 42V

TYPICAL APPLICATIONS

5V Step-Down Converter

IN

4.7µF

10nF

f

SW

1µF

18.2k

= 2MHz

IN

EN/UV

SYNC

TR/SS

INTV

RT

CC

LT8610

PGND

GND

BSTV

SW

BIAS

0.1µF

2.5µH

100k

PG

FB

1M

10pF

243k

47µF

POWER GOOD

V
5V

2.5A

3.8V TO 27V

IN

3.3V Step-Down Converter

LT8610

PGND

BSTV

SW

BIAS

FB

GND

4.7µF

10nF

f

SW

1µF

= 2MHz

18.2k

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

CC

0.1µF

1.8µH

4.7pF

412k

1M

47µF

V

3.3V

2.5A

3.3V Step-Down Converter5V Step-Down Converter

IN

4.7µF

10nF

f

SW

1µF

110k

= 400kHz

IN

EN/UV

SYNC

TR/SS

INTV

RT

CC

LT8610

PGND

GND

BSTV

SW

BIAS

0.1µF
10µH

100k

PG

FB

1M

10pF

243k

68µF

POWER GOOD

V
5V

2.5A

IN

4.7µF

10nF

f

SW

1µF

110k

= 400kHz

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

CC

LT8610

PGND

GND

BSTV

SW

BIAS

0.1µF

8.2µH

FB

1M

4.7pF

412k

68µF

V

3.3V

2.5A

18

For more information www.linear.com/LT8610

8610fa

TYPICAL APPLICATIONS

8610 TA06

OUT

V

(42V TRANSIENT)

8610 TA07

OUT

V

3.4V TO 42V

LT8610

V

12.5V TO 42V

12V Step-Down Converter

IN

4.7µF

10nF

f

SW

1µF

= 1MHz

41.2k

IN

EN/UV

SYNC

TR/SS

INTV

RT

CC

LT8610

PGND

GND

BSTV

SW

BIAS

0.1µF
10µH

100k

PG

FB

1M

10pF

88.7k

8610 TA09

V
12V

2.5A

47µF

POWER GOOD

OUT

IN

1.8V Step-Down Converter

LT8610

PGND

BSTV

SW

BIAS

GND

10nF

f

SW

4.7µF

1µF

= 400kHz

110k

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

CC

0.1µF

4.7µH

866k

FB

4.7pF

1M

120µF

V

1.8V

2.5A

1.8V 2MHz Step-Down Converter

IN

3.4V TO 15V

4.7µF

10nF

f

SW

1µF

= 2MHz

18.2k

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

CC

LT8610

PGND

GND

BSTV

SW

BIAS

0.1µF
1µH

FB

866k

4.7pF

1M

68µF

V

1.8V

2.5A

5.5V TO 42V

V

IN

FB1: TDK MPZ2012S221A

Ultralow EMI 5V 2.5A Step-Down Converter

FB1

4.7µH

4.7µF4.7µF

4.7µF

10nF

1µF

f

52.3k

= 800kHz

SW

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

CC

LT8610

PGND

BSTV

SW

BIAS

FB

GND

BEAD

243k

8610 TA11

0.1µF

4.7µH

1M

10pF

47µF

V
5V

2.5A

OUT

8610fa

For more information www.linear.com/LT8610

19

LT8610

(.0120

NO MEASUREMENT PURPOSE

MSE Package

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

16-Lead Plastic MSOP, Exposed Die Pad

(Reference LTC DWG # 05-08-1667 Rev E)

BOTTOM VIEW OF

EXPOSED PAD OPTION

2.845 ± 0.102
(.112 ± .004)

0.889 ± 0.127
(.035 ± .005)

2.845 ± 0.102
(.112 ± .004)

1

8

0.35
REF

5.23

(.206)

MIN

0.305 ± 0.038
± .0015)

TYP

RECOMMENDED SOLDER PAD LAYOUT

GAUGE PLANE

0.18

(.007)

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.

0.254

(.010)

1.651 ± 0.102
(.065 ± .004)

(.0197)

DETAIL “A”

DETAIL “A”

0.50

BSC

0° – 6° TYP

0.53 ± 0.152

(.021 ± .006)

3.20 – 3.45

(.126 – .136)

SEATING

PLANE

4.90 ± 0.152

(.193 ± .006)

(.043)

0.17 –0.27

(.007 – .011)

TYP

16

4.039 ± 0.102
(.159 ± .004)

(NOTE 3)

1615 1413 1211 10

1 2 3 4 5 6 7 8

1.10

MAX

0.50

(.0197)

BSC

1.651 ± 0.102
(.065 ± .004)

DETAIL “B”

9

9

3.00 ± 0.102

(.118 ± .004)

(NOTE 4)

0.12 REF

DETAIL “B”

CORNER TAIL IS PART OF

THE LEADFRAME FEATURE.

FOR REFERENCE ONLY

0.280 ± 0.076
(.011 ± .003)

REF

0.86

(.034)

REF

0.1016 ± 0.0508
(.004 ± .002)

MSOP (MSE16) 0911 REV E

20

8610fa

For more information www.linear.com/LT8610

LT8610

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

A 10/13 Added H-grade version ABS Max table, Order Information

Clarified Feedback Voltage specification to 150°C
Clarified 3.3V and 5V Efficiency graphs
Clarified RT Programmed Switching Frequency graph

2
2
4
7

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 representa­tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

For more information www.linear.com/LT8610

8610fa

21

LT8610

OUT1

V

3.8V TO 42V

8610 TA08

OUT2

TYPICAL APPLICATION

3.3V and 1.8V with Ratio Tracking Ultralow IQ 2.5V, 3.3V Step-Down with LDO

IN

10nF

f

SW

4.7µF

24.3k

10k

1µF

f

SW

4.7µF

= 500kHz

= 500kHz

IN

EN/UV

PG

LT8610

SYNC

TR/SS

1µF

INTV

CC

RT

PGND

88.7k

IN

EN/UV

PG

LT8610

SYNC

TR/SS

INTV

CC

RT

PGND

88.7k

RELATED PARTS

GND

GND

BSTV

BIAS

BSTV

BIAS

V

0.1µF

5.6µH

SW

232k

FB

4.7pF

97.6k

0.1µF

3.3µH

SW

80.6k

FB

4.7pF

93.1k

47µF

68µF

V

3.3V

2.5A

V

1.8V

2.5A

3.8V TO 27V

IN

10nF

f

4.7µF

SW

1µF

= 2MHz

IN

EN/UV

PG

SYNC

TR/SS

INTV

RT

18.2k

CC

LT8610

PGND

GND

BSTV

SW

BIAS

0.1µF

1.8µH

1M

FB

4.7pF

412k

47µF

IN

LT3008-2.5

SHDN

OUT

SENSE

8610 TA10

V

3.3V

2.5A

OUT1

2.2µF

V

OUT2

2.5V
20mA

PART NUMBER DESCRIPTION COMMENTS

LT8611 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous Micropower Step-Down

DC/DC Converter with I

= 2.5µA and Input/Output Current Limit/Monitor

Q

LT3690 36V with 60V Transient Protection, 4A, 92% Efficiency, 1.5MHz

Synchronous Micropower Step-Down DC/DC Converter with I

= 70µA

Q

LT3971 38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC

Converter with I

= 2.8µA

Q

LT3991 55V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC

Converter with I

LT3970 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC

Converter with I

LT3990 62V, 350mA, 2.2MHz High Efficiency MicroPower Step-Down DC/DC

Converter with I

LT3480 36V with Transient Protection to 60V, 2A (I

= 2.8µA

Q

= 2.5µA

Q

= 2.5µA

Q

), 2.4MHz, High Efficiency

OUT

Step-Down DC/DC Converter with Burst Mode Operation

LT3980 58V with T

ransient Protection to 80V, 2A (I

), 2.4MHz, High Efficiency

OUT

Step-Down DC/DC Converter with Burst Mode Operation

: 3.4V to 42V, V

V

IN

I

< 1µA, 3mm × 5mm QFN-24 Package

SD

: 3.9V to 36V, V

V

IN

I

< 1µA, 4mm × 6mm QFN-26 Package

SD

: 4.2V to 38V, V

V

IN

I

< 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages

SD

: 4.2V to 55V, V

V

IN

I

< 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages

SD

: 4.2V to 40V, V

V

IN

I

< 1µA, 3mm × 2mm DFN-10 and MSOP-10 Packages

SD

: 4.2V to 62V, V

V

IN

I

< 1µA, 3mm × 3mm DFN-10 and MSOP-6E Packages

SD

VIN: 3.6V to 36V, Transient to 60V, V
I

= 70µA, ISD < 1µA, 3mm × 3mm DFN-10 and

Q

= 0.97V, IQ = 2.5µA,

OUT(MIN)

= 0.985V, IQ = 70µA,

OUT(MIN)

= 1.21V, IQ = 2.8µA,

OUT(MIN)

= 1.21V, IQ = 2.8µA,

OUT(MIN)

= 1.21V, IQ = 2.5µA,

OUT(MIN)

= 1.21V, IQ = 2.5µA,

OUT(MIN)

OUT(MIN)

= 0.78V,

MSOP-10E Packages

VIN: 3.6V to 58V, Transient to 80V, V
I

= 85µA, ISD < 1µA, 3mm × 4mm DFN-16 and

Q

OUT(MIN)

= 0.78V,

MSOP-16E Packages

22

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

For more information www.linear.com/LT8610

●

www.linear.com/LT8610

8610fa

LT 1013 REV A • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 2012