LINEAR TECHNOLOGY LTC3827-1 Technical data

查询LTC3827-1供应商

FEATURES

■

Wide Output Voltage Range: 0.8V ≤ V

■

Low Operating IQ: 80µA (One Channel On)

■

Out-of-Phase Controllers Reduce Required Input

OUT

≤ 10V

Capacitance and Power Supply Induced Noise

■

OPTI-LOOP® Compensation Minimizes C

■

±1% Output Voltage Accuracy

■

Wide VIN Range: 4V to 36V Operation

■

Phase-Lockable Fixed Frequency 140kHz to 650kHz

■

Selectable Continuous, Pulse Skipping or Low Ripple
Burst Mode

■

Dual N-Channel MOSFET Synchronous Drive

■

Very Low Dropout Operation: 99% Duty Cycle

■

Adjustable Output Voltage Soft-Start or Tracking

■

Output Current Foldback Limiting

■

Power Good Output Voltage Monitor

■

Output Overvoltage Protection

■

Low Shutdown IQ: 8µA

■

Internal LDO Powers Gate Drive from VIN or V

■

Small 28-Lead SSOP Package

®

Operation at Light Loads

OUT

OUT

U

APPLICATIO S

■

Automotive Systems

■

Battery-Operated Digital Devices

■

Distributed DC Power Systems

LTC3827-1

Low IQ, Dual, 2-Phase

Synchronous Controller

U

DESCRIPTIO

The LTC
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant fre­quency current mode architecture allows a phase-lock­able frequency of up to 650kHz. Power loss and noise due
to the ESR of the input capacitor ESR are minimized by
operating the two controller output stages out of phase.

The 80µA no-load quiescent current extends operating life
in battery powered systems. OPTI-LOOP compensation
allows the transient response to be optimized over a wide
range of output capacitance and ESR values. The
LTC3827-1 features a precision 0.8V reference and a
power good output indicator. A wide 4V to 36V input
supply range encompasses all battery chemistries.

Independent TRACK/SS pins for each controller ramp the
output voltage during startup. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.

The PLLIN/MODE pin selects among Burst Mode opera­tion, pulse skipping mode, or continuous inductor current
mode at light loads. For a leadless package version
(5mm x 5mm QFN) with additional features, see the
LTC3827 datasheet.

and OPTI-LOOP are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents, including
5481178, 5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6304066, 5705919.

®

3827-1 is a high performance dual step-down

, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode

TYPICAL APPLICATIO

High Efficiency Dual 8.5V/3.3V Step-Down Converter

+

4.7µF

TG1 TG2

3.3µH

0.015Ω

V

OUT1

3.3V
5A

62.5k

150µF

20k

0.1µF

15k

BOOST1 BOOST2

SW1 SW2

BG1 BG2

SENSE1

SENSE1

V

FB1

I

TH1

220pF

TRACK/SS1 TRACK/SS2

0.1µF

V

IN

+

–

U

LTC3827-1

SGND

INTV

CC

PGND

SENSE2

SENSE2

Efficiency and Power Loss

V

IN

4V TO 36V

20k

22µF
50V

7.2µH

0.015Ω

192.5k

150µF

38271 TA01

V

8.5V

3.5A

OUT2

1µF

0.1µF

+

–

V

FB2

I

TH2

0.1µF

220pF

15k

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0.001

vs Load Current

EFFICIENCY

= 12V; V

V

IN

0

0.01 0.1 1 10 100 1000 10000
LOAD CURRENT (mA)

FIGURE 13 CIRCUIT

= 3.3V

OUT

POWER LOSS

38271 TA01b

100000

10000

POWER LOSS (mW)

1000

100

10

1

0.1

38271f

1

LTC3827-1

PACKAGE/ORDER I FOR ATIO

UU

W

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Input Supply Voltage (VIN).........................36V to –0.3V

Top Side Driver Voltages

(BOOST1, BOOST2)...............................42V to – 0.3V

Switch Voltage (SW1, SW2) .........................36V to – 5V

(BOOST1-SW1), (BOOST2-SW2) ............... 8.5V to – 0.3V

RUN1, RUN2 .............................................. 7V to –0.3V

SENSE1

PLLIN/MODE, PLLLPF, TRACK/SS1, TRACK/SS2

EXTV
I

TH1, ITH2

PGOOD1 Voltage ...................................... 8.5V to –0.3V

Peak Output Current <10µs (TG1, TG2, BG1, BG2) ... 3A

INTVCC Peak Output Current ................................ 50mA

Operating Temperature Range (Note 2) .. – 40°C to 85°C

Junction Temperature (Note 3)............................. 125°C

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

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

+

, SENSE2+, SENSE1–,

–

SENSE2

Voltages ................................11V to –0.3V

Voltages .......................................... INTV

......................................................10V to –0.3V

CC

, V

, V

FB1

Voltages ..................2.7V to –0.3V

FB2

to –0.3V

CC

TOP VIEW

1

I

TH1

2

V

FB1

+

SENSE1

SENSE1

PLLIN/MODE

SENSE2

SENSE2

TRACK/SS2

3

–

4

5

PLLLPF

6

7

SGND

8

RUN1

9

RUN2

–

10

+

11

12

V

FB2

13

I

TH2

14

28-LEAD PLASTIC SSOP

T

JMAX

G PACKAGE

= 125°C, θJA = 95°C/W

ORDER PART NUMBER

LTC3827EG-1

TRACK/SS1

28

PGOOD1

27

TG1

26

SW1

25

BOOST1

24

BG1

23

V

22

IN

PGND

21

EXTV

20

CC

INTV

19

CC

BG2

18

BOOST2

17

SW2

16

TG2

15

G PART MARKING

LTC3827EG-1

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/

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

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 12V, V

A

RUN/SS1, 2

= 5V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Main Control Loops

V

FB1, 2

I

VFB1, 2

V

REFLNREG

V

LOADREG

g

m1, 2

I

Q

UVLO Undervoltage Lockout VIN Ramping Down

V

OVL

I

SENSE

DF

MAX

Regulated Feedback Voltage (Note 4); I

Voltage = 1.2V

TH1, 2

●

0.792 0.800 0.808 V
Feedback Current (Note 4) –5 –50 nA

Reference Voltage Line Regulation VIN = 4V to 30V (Note 4) 0.002 0.02 %/V
Output Voltage Load Regulation (Note 4)

Transconductance Amplifier g

Measured in Servo Loop; ∆I
Measured in Servo Loop; ∆I

I

m

= 1.2V; Sink/Source 5µA (Note 4) 1.55 mmho

TH1, 2

Voltage = 1.2V to 0.7V

TH

Voltage = 1.2V to 2V

TH

●

●

0.1 0.5 %

–0.1 –0.5 %

Input DC Supply Current (Note 5)
Sleep Mode (Channel 1 On) RUN1 = 5V, RUN2 = 0V, V
Sleep Mode (Channel 2 On) RUN1 = OV, RUN2 = 5V, V
Shutdown V
Sleep Mode (Both Channels) RUN1,2 = 5V, V

Feedback Overvoltage Lockout Measured at V

Sense Pins Total Source Current (Each Channel) V

= 0V 8 20 µA

RUN1, 2

= V

FB1

, Relative to Regulated V

FB1, 2

SENSE1–, 2–

= 0.83V (No Load) 80 125 µA

FB1

= 0.83V (No Load) 80 125 µA

FB2

= 0.83V 115 160 µA

FB2

= V

SENSE1+, 2+

●

FB1, 2

81012 %

= 0V –660 µA

3.5 4 V

Maximum Duty Factor In Dropout 98 99.4 %

38271f

2

LTC3827-1

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 12V, V

A

RUN/SS1, 2

= 5V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

TRACK/SS1, 2

V

RUN1, 2

V

SENSE(MAX)

Soft-Start Charge Current V

ON RUN Pin ON Threshold V

Maximum Current Sense Threshold V

TRACK1, 2

RUN1, VRUN2

= 0.7V,V

FB1, 2

= 0.7V,V

V

FB1, 2

= 0V 0.75 1.0 1.35 µA

Rising 0.5 0.7 0.9 V

–

SENSE1–, 2
SENSE1–, 2

= 3.3V 90 100 110 mV

–

= 3.3V

●

80 100 115 mV

TG Transition Time: (Note 6)
TG1, 2 t
TG1, 2 t

Rise Time C

r

Fall Time C

f

= 3300pF 50 90 ns

LOAD

= 3300pF 50 90 ns

LOAD

BG Transition Time: (Note 6)
BG1, 2 t
BG1, 2 t

TG/BG t

Rise Time C

r

Fall Time C

f

Top Gate Off to Bottom Gate On Delay C

1D

= 3300pF 40 90 ns

LOAD

= 3300pF 40 80 ns

LOAD

= 3300pF Each Driver 70 ns

LOAD

Synchronous Switch-On Delay Time

BG/TG t

Bottom Gate Off to Top Gate On Delay C

2D

= 3300pF Each Driver 70 ns

LOAD

Top Switch-On Delay Time

t

ON(MIN)

Minimum On-Time (Note 7) 180 ns

INTVCC Linear Regulator

V

INTVCCVIN

V

LDOVIN

V

INTVCCEXT

V

LDOEXT

V

EXTVCC

V

LDOHYS

Internal VCC Voltage 8.5V < VIN < 30V, V

INTVCC Load Regulation ICC = 0mA to 20mA, V

Internal VCC Voltage V

= 8.5V 7.2 7.5 7.8 V

EXTVCC

INTVCC Load Regulation ICC = 0mA to 20mA, V

EXTVCC Switchover Voltage ICC = 20mA, EXTV

= 0V 5.0 5.25 5.5 V

EXTVCC

= 0V 0.2 1.0 %

EXTVCC

= 8.5V 0.2 1.0 %

EXTVCC

Ramping Positive 4.5 4.7 V

CC

EXTVCC Hysteresis 0.2 V

Oscillator and Phase-Locked Loop

f

NOM

f

LOW

f

HIGH

f

SYNCMIN

f

SYNCMAX

I

PLLLPF

Nominal Frequency V

Lowest Frequency V

Highest Frequency V

= Floating; PLLIN/MODE = DC Voltage 360 400 440 kHz

PLLLPF

= 0V; PLLIN/MODE = DC Voltage 220 250 280 kHz

PLLLPF

= INTVCC; PLLIN/MODE = DC Voltage 475 530 580 kHz

PLLLPF

Minimum Synchronizable Frequency PLLIN/MODE = External Clock; V

Maximum Synchronizable Frequency PLLIN/MODE = External Clock; V

Phase Detector Output Current

Sinking Capability f
Sourcing Capability f

PLLIN/MODE
PLLIN/MODE

< f
> f

OSC
OSC

= 0V 115 140 kHz

PLLLPF

= 2V 650 800 kHz

PLLLPF

–5 µA
5 µA

PGOOD Output

V

PGL

I

PGOOD

V

PG

PGOOD Voltage Low I

PGOOD Leakage Current V

= 2mA 0.1 0.3 V

PGOOD

= 5V ±1 µA

PGOOD

PGOOD Trip Level VFB with Respect to Set Regulated Voltage

Ramping Negative –12 –10 –8 %

V

FB

V

Ramping Positive 8 10 12 %

FB

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

Note 2: The LTC3827E-1 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: T
dissipation P

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

= TA + (PD • 95 °C/W)

T

J

Note 4: The LTC3827-1 is tested in a feedback loop that servos V
a specified voltage and measures the resultant V

FB1, 2.

ITH1, 2

to

Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.

Note 6: Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.

Note 7: The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥40% of I

(see minimum on-time

MAX

considerations in the Applications Information section).

38271f

3

LTC3827-1

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Efficiency and Power Loss
vs Output Current Efficiency vs Load Current

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.001

Burst Mode OPERATION
FORCED CONTINUOUS MODE
PULSE SKIPPING MODE

VIN = 12V

= 3.3V

V

OUT

0.01 0.1 1 10 100 1000 10000
LOAD CURRENT (mA)

FIGURE 13 CIRCUIT

10000

1000

100

10

1

0.1

38271 G01

100

90

POWER LOSS (mW)

80

70

EFFICIENCY (%)

60

50

40

0.001

FIGURE 13 CIRCUIT

VIN = 12V

= 5V

V

IN

= 3.3V

V

OUT

0.01 0.1 1 10 100 1000 10000
LOAD CURRENT (mA)

38271 G02

Efficiency vs Input Voltage

98

96

94

92

90

88

EFFICIENCY (%)

86

84

V

= 3.3V

OUT

82

51015203040

0

INPUT VOLTAGE (V)

FIGURE 13 CIRCUIT

25 35

38271 G03

V

100mV/DIV

COUPLED

2A/DIV

FORCED

CONTINUOUS

MODE

2A/DIV

BURST MODE

PULSE

SKIPPING

MODE

Load Step
(Burst Mode Operation)

OUT

AC

I

L

20µs/DIV

FIGURE 13 CIRCUIT
V

= 3.3V

OUT

Inductor Current at Light Load

FIGURE 13 CIRCUIT

= 3.3V

V

OUT

I

= 300µA

LOAD

4µs/DIV

38271 G04

38271 G07

V

OUT

100mV/DIV

AC

COUPLED

2A/DIV

Load Step
(Forced Continuous Mode)

I

L

20µs/DIV

FIGURE 13 CIRCUIT

= 3.3V

V

OUT

Soft Start-Up

FIGURE 13 CIRCUIT

20ms/DIV

38271 G05

V

OUT2

2V/DIV

V

OUT1

2V/DIV

38271 G08

V

OUT

100mV/DIV

AC

COUPLED

2A/DIV

Load Step
(Pulse Skip Mode)

I

L

20µs/DIV

FIGURE 13 CIRCUIT
V

= 3.3V

OUT

Tracking Start-Up

FIGURE 13 CIRCUIT

20ms/DIV

38271 G06

V

OUT2

2V/DIV

V

OUT1

2V/DIV

38271 G09

4

38271f

UW

DUTY CYCLE (%)

0

CURRENT SENSE THRESHOLD (mV)

40

80

120

20

60

100

20 40 60 80

38271 G15

10010030507090

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3827-1

Total Input Supply Current
vs Input Voltage

350

300

250

200

150

100

SUPPLY CURRENT (µA)

50

300µA LOAD

NO LOAD

0

5

10 15

20 30

INPUT VOLTAGE (V)

FIGURE 13 CIRCUIT

Maximum Current Sense Voltage

Voltage

vs I

TH

100

–20

CURRENT SENSE THRESHOLD (mV)

–40

PULSE SKIPPING
FORCED CONTINUOUS

80

BURST MODE (RISING)
BURST MODE (FALLING)

60

40

20

0

0

0.2 0.4

10% Duty Cycle

0.8 1.2 1.4

0.6 1.0

ITH PIN VOLTAGE (V)

25 35

38271 G10

38271 G13

EXTVCC Switchover and INTV
Voltages vs Temperature

6.0

5.8

5.6

5.4

5.2

VOLTAGES (V)

CC

5.0

4.8

4.6

AND INTV

CC

4.4

EXTV

4.2

4.0
–45

–25

15

–5

TEMPERATURE (°C)

Sense Pins Total Input
Bias Current

200

100

0

–100

–200

–300

–400

INPUT CURRENT (µA)

–500

–600

–700

12345 10

0

V

COMMON MODE VOLTAGE (V)

SENSE

INTVCC

EXTVCC RISING

EXTVCC FALLING

35

55

6789

CC

75 95

38271 G11

38271 G14

Line Regulation

INTV

CC

5.50

5.45

5.40

5.35

5.30

5.25

VOLTAGE (V)

5.20

CC

5.15

INTV

5.10

5.05

5.00
0

515

10

INPUT VOLTAGE (V)

Maximum Current Sense
Threshold vs Duty Cycle

35

20

30

25

40

38271 G12

Foldback Current Limit Quiescent Current vs Temperature

120

TRACK/SS = 1V

100

80

60

40

20

MAXIMUM CURRENT SENSE VOLTAGE (V)

0

0.1 0.3

0.2

0

FEEDBACK VOLTAGE (V)

0.7

0.5 0.9

0.6

0.4

0.8

38271 G16

100

PLLIN/MODE = 0V

95

90

85

80

75

70

QUIESCENT CURRENT (µA)

65

60

–30 90

–45

–15

15

0

TEMPERATURE (°C)

SENSE Pins Total Input
Bias Current vs I

12

V

= 3.3V

SENSE

10

8

6

4

INPUT CURRENT (µA)

2

0

30

75

45

60

38271 G17

0

0.2

TH

0.4 0.6 0.8 1 1.2 1.4
ITH VOLTAGE (V)

38271 G18

38271f

5

LTC3827-1

UW

TYPICAL PERFOR A CE CHARACTERISTICS

TRACK/SS Pull-Up Current
vs Temperature

1.20

1.15

1.10

1.05

1.00

0.95

TRACK/SS CURRENT (µA)

0.90

0.85

0.80
–30 90

–45

–15

15

30

0

TEMPERATURE (°C)

Sense Pins Total Input Current
vs Temperature

INPUT CURRENT (µA)

200

100

–100

–200

–300

–400

–500

–600

–700

–800

0

–45

–30 0

V

= 10V

OUT

V

= 3.3V

OUT

V

= OV

OUT

–15

15

TEMPERATURE (°C)

30 90

Shutdown (RUN) Threshold
vs Temperature

1.00

0.95

0.90

0.85

0.80

0.75

0.70

0.65

RUN PIN VOLTAGE (V)

0.60

0.55

75

45

60

38271 G19

0.50
–30 90

–45

–15

15

30

0

TEMPERATURE (°C)

75

45

60

38271 G20

Shutdown Current
vs Input Voltage

25

20

15

10

INPUT CURRENT (µA)

5

60

75

45

38271 G22

0

510

25

20

15

INPUT VOLTAGE (V)

30

35

38271 G23

Regulated Feedback Voltage
vs Temperature

808

806

804

802

800

798

796

794

REGULATED FEEDBACK VOLTAGE (mV)

792

–30 90

–45

–15

15

30

0

TEMPERATURE (°C)

Oscillator Frequency
vs Temperature

800

700

600

500

400

300

FREQUENCY (kHz)

200

100

0

–45

–25

–5

V

= INTVCC

PLLLPF

V

= FLOAT

PLLLPF

V

= GND

PLLLPF

35

15

TEMPERATURE (°C)

75

45

60

38271 G21

75 95

38271 G24

55

Undervoltage Lockout Threshold
vs Temperature

4.2

4.1

4.0

3.9

3.8

3.7

VOLTAGE (V)

3.6

CC

3.5

INTV

3.4

3.3

3.2
–45

–30

RISING

FALLING

15

0

–15

TEMPERATURE (°C)

6

Oscillator Frequency
vs Input Voltage

404

402

400

398

396

FREQUENCY (kHz)

394

30

604575 90

38271 G25

392

510

15

INPUT VOLTAGE (V)

25

20

30

35

38271 G26

Shutdown Current
vs Temperature

12

10

8

6

4

SHUTDOWN CURRENT (µA)

2

0

–30 90

–45

–15

15

0

TEMPERATURE (°C)

30

75

45

60

38271 G27

38271f

LTC3827-1

U

UU

PI FU CTIO S

I

TH1, ITH2

Switching Regulator Compensation Points. Each associa­ted channel’s current comparator trip point increases
with this control voltage.

V

FB1

feedback voltage for each controller from an external
resistive divider across the output.

SENSE1

Differential Current Comparators. The I
controlled offsets between the SENSE
in conjunction with R

SENSE1

Differential Current Comparators.

PLLLPF (Pin 5): The phase-locked loop’s lowpass filter
is tied to this pin when synchronizing to an external
clock. Alternatively, tie this pin to GND, INTV
floating to select 250kHz, 530kHz or 400kHz switching
frequency.

PLLIN/MODE (Pin 6): External Synchronization Input to
Phase Detector and Forced Continuous Control Input. When
an external clock is applied to this pin, the phase-locked
loop will force the rising TG1 signal to be synchronized
with the rising edge of the external clock. In this case, an
R-C filter must be connected to the PLLLPF pin. When not
synchronizing to an external clock, this input, which acts
on both controllers, determines how the LTC3827-1 oper­ates at light loads. Pulling this pin below 0.7V selects Burst
Mode operation. Tying this pin to INTV
ous inductor current operation. Tying this pin to a voltage
greater than 0.9V and less than INTV
skipping operation.

SGND (Pin 7): Small Signal Ground common to both
controllers, must be routed separately from high current
grounds to the common (–) terminals of the C

RUN1, RUN2 (Pins 8, 9): Digital Run Control Inputs for
Each Controller. Forcing either of these pins below 0.7V
shuts down that controller. Forcing both of these pins
below 0.7V shuts down the entire LTC3827-1, reducing
quiescent current to approximately 8µA.

INTV

Regulator. The driver and control circuits are powered from

(Pins 1, 13): Error Amplifier Outputs and

, V

(Pins 2, 12): Receives the remotely sensed

FB2

+

, SENSE2+ (Pins 3, 11): The (+) Input to the

pin voltage and

TH

–

and SENSE+ pins

set the current trip threshold.

SENSE

–

, SENSE2– (Pins 4, 10): The (–) Input to the

or leave

CC

forces continu-

CC

–0.5V selects pulse

CC

capacitors.

IN

(Pin 19): Output of the Internal Linear Low Dropout

CC

this voltage source. Must be decoupled to power ground with
a minimum of 4.7µF tantalum or other low ESR capacitor.

EXTV

Connected to INTV
bypassing the internal
EXTV

(Pin 20): External Power Input to an Internal LDO

CC

. This LDO supplies INTVCC power,

CC

LDO powered from VIN whenever

is higher than 4.7V. See EXTVCC Connection in the

CC

Applications Information section. Do not exceed 10V on
this pin.

PGND (Pin 21): Driver Power Ground. Connects to the
sources of bottom (synchronous) N-channel MOSFETs, an­odes of the Schottky rectifiers and the (–) terminal(s) of C

IN

.

VIN (Pin 22): Main Supply Pin. A bypass capacitor should
be tied between this pin and the signal ground pin.

BG1, BG2 (Pins 23, 18): High Current Gate Drives for
Bottom (Synchronous) N-Channel MOSFETs. Voltage
swing at these pins is from ground to INTV

CC

.

BOOST1, BOOST2 (Pins 24, 17): Bootstrapped Supplies
to the Top Side Floating Drivers. Capacitors are connected
between the BOOST and SW pins and Schottky diodes are
tied between the BOOST and INTV
at the BOOST pins is from INTV

pins. Voltage swing

CC

to (VIN + INTVCC).

CC

SW1, SW2 (Pins 25, 16): Switch Node Connections to
Inductors. Voltage swing at these pins is from a Schottky
diode (external) voltage drop below ground to VIN.

TG1, TG2 (Pins 26, 15): High Current Gate Drives for Top
N-Channel MOSFETs. These are the outputs of floating
drivers with a voltage swing equal to INTV

CC

– 0.5V

superimposed on the switch node voltage SW.

PGOOD1 (Pin 27): Open-Drain Logic Output. PGOOD1 is
pulled to ground when the voltage on the V

pin is not

FB1

within ±10% of its set point.

TRACK/SS1, TRACK/SS2 (Pins 28, 14): External Tracking
and Soft-Start Input. The LTC3827-1 regulates the V

FB1,2

voltage to the smaller of 0.8V or the voltage on the TRACK/
SS1,2 pin. A internal 1µA pull-up current source is con-
nected to this pin. A capacitor to ground at this pin sets the
ramp time to final regulated output voltage. Alternatively,
a resistor divider on another voltage supply connected to
this pin allows the LTC3827-1 output to track the other
supply during startup.

38271f

7

LTC3827-1

U

U

W

FU CTIO AL DIAGRA

PLLIN/MODE

F

6

IN

PLLLPF

5

R

LP

C

LP

PGOOD1

27

V

IN

22

V

IN

EXTV

20

INTV

19

+

SGND

7

PLLIN/MODE

CC

CC

PHASE DET

100k

OSCILLATOR

INTVCC-0.5V

4.7V

0.8V

CLK1

CLK2

–

0.88V

+

V

FB1

–

+

0.72V

–

FC

+

–

BURSTEN

+

+

–

5V/

7.5V
LDO

INTERNAL

SUPPLY

DUPLICATE FOR SECOND
CONTROLLER CHANNEL

ICMP IR

0.45V

2(VFB)

SLOPE

COMP

0.5µA

6V

RUN
8, 9

SRQ

+

–

Q

0.4V

DROP

OUT

DET

+

–

+– –+

SHDN

RST

2(VFB)

BOT

B

6mV

TOP ON

BURSTEN

SLEEP

SHDN

FOLDBACK

INTV

BOOST

24, 17

INTV

CC

PGND

SENSE

SENSE

V

TRACK/SS

TG

SW

BG

I

26, 15

25, 16

23, 18

21

+

3, 11

–

4, 10

FB

2, 12

TH

1,13

28,14

TOP

FC

SWITCH

LOGIC

BOT

–

+

V

FB

–

TRACK/SS

EA

+

0.80V

OV

+

–

0.88V

1µA

SHDN

V

CC

IN

D

B

C

B

L

R

B

R

A

C

C

R

C

C

C2

C

SS

D

R

SENSE

C

IN

C

OUT

V

OUT

8

38271 FD

38271f

OPERATIO

LTC3827-1

U

(Refer to Functional Diagram)

Main Control Loop

The LTC3827-1 uses a constant frequency, current mode
step-down architecture with the two controller channels
operating 180 degrees out of phase. During normal opera­tion, each external top MOSFET is turned on when the
clock for that channel sets the RS latch, and is turned off
when the main current comparator, I
latch. The peak inductor current at which I
resets the latch is controlled by the voltage on the I

, resets the RS

CMP

trips and

CMP

TH

pin,
which is the output of the error amplifier EA. The error
amplifier compares the output voltage feedback signal at
the V
divider connected across the output voltage, V

pin, (which is generated with an external resistor

FB

, to

OUT

ground) to the internal 0.800V reference voltage. When
the load current increases, it causes a slight decrease in
V

relative to the reference, which causes the EA to

FB

increase the I

voltage until the average inductor current

TH

matches the new load current.

After the top MOSFET is turned off each cycle, the bottom
MOSFET is turned on until either the inductor current
starts to reverse, as indicated by the current comparator
IR, or the beginning of the next clock cycle.

INTV

/EXTVCC Power

CC

Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTV

CC

pin.
When the EXTVCC pin is left open or tied to a voltage less
than 4.7V, an internal 5V low dropout linear regulator
supplies INTV

power from VIN. If EXTVCC is taken above

CC

4.7V, the 5V regulator is turned off and a 7.5V low dropout
linear regulator is enabled that supplies INTV
from EXTV

. If EXTVCC is less than 7.5V (but greater than

CC

4.7V), the 7.5V regulator is in dropout and INTV
approximately equal to EXTV

. When EXTVCC is greater

CC

power

CC

CC

is

than 7.5V (up to an absolute maximum rating of 10V),
INTV

is regulated to 7.5V. Using the EXTVCC pin allows

CC

the INTVCC power to be derived from a high efficiency
external source such as one of the LTC3827-1 switching
regulator outputs.

Each top MOSFET driver is biased from the floating boot­strap capacitor C

, which normally recharges during each

B

off cycle through an external diode when the top MOSFET
turns off. If the input voltage V

decreases to a voltage

IN

close to V

, the loop may enter dropout and attempt to

OUT

turn on the top MOSFET continuously. The dropout detec­tor detects this and forces the top MOSFET off for about
one twelfth of the clock period every tenth cycle to allow C

B

to recharge.

Shutdown and Start-Up (RUN1, RUN2 and TRACK/
SS1, TRACK/SS2 Pins)

The two channels of the LTC3827-1 can be independently
shut down using the RUN1 and RUN2 pins. Pulling either
of these pins below 0.7V shuts down the main control loop
for that controller. Pulling both pins low disables both
controllers and most internal circuits, including the
INTV

regulator, and the LTC3827-1 draws only 8µA of

CC

quiescent current.

Releasing either RUN pin allows an internal 0.5µA current
to pull up the pin and enable that controller. Alternatively,
the RUN pin may be externally pulled up or driven directly
by logic. Be careful not to exceed the Absolute Maximum
rating of 6V on this pin.

The start-up of each controller’s output voltage V

OUT

is con­trolled by the voltage on the TRACK/SS1 and TRACK/SS2
pin. When the voltage on the TRACK/SS pin is less than the

0.8V internal reference, the LTC3827-1 regulates the V

FB

voltage to the TRACK/SS pin voltage instead of the 0.8V
reference. This allows the TRACK/SS pin to be used to
program a soft start by connecting an external capacitor
from the TRACK/SS pin to SGND. An internal 1µA pull-up
current charges this capacitor creating a voltage ramp on
the TRACK/SS pin. As the TRACK/SS voltage rises linearly
from 0V to 0.8V (and beyond), the output voltage V

OUT

rises smoothly from zero to its final value.

Alternatively the TRACK/SS pin can be used to cause the
startup of V

to “track” that of another supply. Typically,

OUT

this requires connecting to the TRACK/SS pin an external
resistor divider from the other supply to ground (see
Applications Information section).

When the corresponding RUN pin is pulled low to disable
a controller, or when V

drops below its undervoltage

IN

lockout threshold of 3.7V, the TRACK/SS pin is pulled low
by an internal MOSFET. When in undervoltage lockout,
both controllers are disabled and the external MOSFETs
are held off.

38271f

9

LTC3827-1

OPERATIO

U

(Refer to Functional Diagram)

Light Load Current Operation (Burst Mode Operation,
Pulse Skipping, or Continuous Conduction)
(PLLIN/MODE Pin)

The LTC3827-1 can be enabled to enter high efficiency
Burst Mode operation, constant frequency pulse skipping
mode, or forced continuous conduction mode at low load
currents. To select Burst Mode operation, tie the PLLIN/
MODE pin to a DC voltage below 0.8V (e.g., SGND). To
select forced continuous operation, tie the PLLIN/MODE
pin to INTV
PLLIN/MODE pin to a DC voltage greater than 0.8V and
less than INTV

When a controller is enabled for Burst Mode operation,
the peak current in the inductor is set to approximately
one-tenth of the maximum sense voltage even though
the voltage on the I
average inductor current is lower than the load current,
the error amplifier EA will decrease the voltage on the
ITH pin. When the ITH voltage drops below 0.4V, the
internal sleep signal goes high (enabling “sleep” mode)
and both external MOSFETs are turned off. The I
is then disconnected from the output of the EA and
“parked” at 0.425V.

In sleep mode, much of the internal circuitry is turned
off, reducing the quiescent current that the LTC3827-1
draws. If one channel is shut down and the other
channel is in sleep mode, the LTC3827-1 draws only
80µA of quiescent current. If both channels are in sleep
mode, the LTC3827-1 draws only 115µA of quiescent
current. In sleep mode, the load current is supplied by
the output capacitor. As the output voltage decreases,
the EA’s output begins to rise. When the output voltage
drops enough, the ITH pin is reconnected to the output
of the EA, the sleep signal goes low, and the controller

. To select pulse-skipping mode, tie the

CC

– 0.5V.

CC

pin indicates a lower value. If the

TH

pin

TH

resumes normal operation by turning on the top exter­nal MOSFET on the next cycle of the internal oscillator.

When a controller is enabled for Burst Mode operation, the
inductor current is not allowed to reverse. The reverse
current comparator (IR) turns off the bottom external
MOSFET just before the inductor current reaches zero,
preventing it from reversing and going negative. Thus, the
controller operates in discontinuous operation.

In forced continuous operation, the inductor current is
allowed to reverse at light loads or under large transient
conditions. The peak inductor current is determined by the
voltage on the I
mode, the efficiency at light loads is lower than in Burst
Mode operation. However, continuous has the advantages
of lower output ripple and less interference to audio
circuitry. In forced continuous mode, the output ripple is
independent of load current.

When the PLLIN/MODE pin is connected for pulse-skip­ping mode or clocked by an external clock source to use
the phase-locked loop (see Frequency Selection and Phase­Locked Loop section), the LTC3827-1 operates in PWM
pulse skipping mode at light loads. In this mode, constant
frequency operation is maintained down to approximately
1% of designed maximum output current. At very light
loads, the current comparator I
several cycles and force the external top MOSFET to stay
off for the same number of cycles (i.e., skipping pulses).
The inductor current is not allowed to reverse (discontinu­ous operation). This mode, like forced continuous opera­tion, exhibits low output ripple as well as low audio noise
and reduced RF interference as compared to Burst Mode
operation. It provides higher low current efficiency than
forced continuous mode, but not nearly as high as Burst
Mode operation.

pin, just as in normal operation. In this

TH

may remain tripped for

CMP

10

38271f