LINEAR TECHNOLOGY LTC1879 Technical data

FEATURES

■

High Efficiency: Up to 95%

■

Low Quiescent Current: Only 15µA with No Load

■

550kHz Constant Frequency Operation

■

2.65V to 10V Input Voltage Range

■

V

from 0.8V to VIN, I

OUT

■

True PLL Frequency Locking from 350kHz to 750kHz

■

Power Good Output Voltage Monitor

■

Low Dropout Operation: 100% Duty Cycle

■

Burst Mode® or Pulse Skipping Operation

■

Current Mode Operation for Excellent Line and Load

OUT

to 1.2A

Transient Response

■

Shutdown Mode Draws <1µA Supply Current

■

±2% Output Voltage Accuracy

■

Overcurrent and Overtemperature Protected

■

Available in 16-Lead SSOP Package

U

APPLICATIO S

■

Cellular Telephones

■

Portable Computers

■

Wireless Modems

LTC1879

1.2A Synchronous

Step-Down Regulator with

15µA Quiescent Current

U

DESCRIPTIO

The LTC®1879 is a high efficiency monolithic synchro­nous buck regulator using a constant frequency, current
mode architecture. Operating supply current is only 15µA
with no load and drops to <1µA in shutdown. The input
supply voltage range of 2.65V to 10V makes the LTC1879
ideally suited for both single and dual Li-Ion battery-pow­ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.

The switching frequency is internally set to 550kHz, allow­ing the use of small surface mount inductors and capaci­tors. For noise sensitive applications, the LTC1879 can be
externally synchronized from 350kHz to 750kHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low.

The internal synchronous rectifier switch increases effi­ciency and eliminates the need for an external Schottky
diode. Low output voltages are easily supported with a

0.8V feedback reference voltage. The LTC1879 is available
in a 16-lead SSOP package.

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

Burst Mode is a registered trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

High Efficiency Step-Down Converter

V

IN

2.65V TO 10V

C
C
L1: TOKO A921CY6R2M
*V

C

IN

10µF

150k

47pF

: TAIYO YUDEN CERAMIC LMK325BJ106MN

IN

: TDK CERAMIC C4532X5ROJ476M

OUT

OUT

220pF

CONNECTED TO VIN (MINUS SWITCH AND L1 VOLTAGE DROP) FOR 2.65V < VIN < 3.1V

2

15

14

4

RUN/SS

SYNC/MODE

PGOOD

I

TH

U

13

SV

IN

LTC1879

SGND

1

PV

SWP

SWN

PGND

V

Efficiency vs Output Load Current

100

90

8, 9

IN

5, 12

6, 11

7, 10

3

FB

28.0k

1879 TA01a

L1

6.2µH

80.6k

V

3.1V

C

OUT

47µF

OUT

*

80

70

60

EFFICIENCY (%)

50

40

30

0.1 10 100

VIN = 3.6V

VIN = 7.2V

VIN = 10V

Burst Mode OPERATION

= 3.1V

V

OUT

L = 6.2µH

1 1000

OUPUT CURRENT (mA)

1879 TA01b

1879f

1

LTC1879

WW

W

ABSOLUTE MAXIMUM RATINGS

U

U

W

PACKAGE/ORDER INFORMATION

U

(Note 1)

Input Supply Voltage ................................ –0.3V to 11V

ITH, PLL_LPF Voltages............................. –0.3V to 2.7V

RUN/SS, VFB Voltages ............................... – 0.3V to V

SYNC/MODE Voltage ................................. –0.3V to V

(V

– V

PVIN

V

Voltage............................................ –0.3V to 11V

SWN

) Voltage............................. –0.3V to 11V

SWP

IN
IN

P-Channel Switch Source Current (DC) .................... 2A

N-Channel Switch Sink Current (DC) ........................ 2A

Peak Switching Sink and Source Current ................. 3A

Operating Ambient Temperature Range

(Note 2) ............................................. –40°C to 85°C

Junction Temperature (Notes 3, 6) ...................... 125°C

TOP VIEW

1

SGND

2

RUN/SS

3

V

FB

4

I

TH

5

SWP1

6

SWN1

7

PGND1

8

PV

IN1

GN PACKAGE

16-LEAD PLASTIC SSOP

T

= 125°C, θJA = 140°C/ W, θJC = 40°C/W

JMAX

16

PLL_LPF

15

SYNC/MODE

14

PGOOD

13

SV

12

SWP2

11

SWN2

10

PGND2

9

PV

IN

IN2

ORDER PART

NUMBER

LTC1879EGN

GN PART

MARKING

1879

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

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

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

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 5V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

VFB

V

FB

∆V

OVL

∆V

UVL

∆VFB/V
V

LOADREG

V

IN

I

Q

f

SYNC

f

OSC

I

PLLLPF

R

PFET

R

NFET

I

PK

I

LSW

V

SYNC/MODE

I

SYNC/MODE

Feedback Current (Note 4) ● 860 nA
Regulated Output Voltage (Note 4) 0°C ≤ TA ≤ 85°C 0.784 0.80 0.816 V

(Note 4) –40°C ≤ T

Overvoltage Trip Limit with Respect to VFB∆V
Undervoltage Trip Limit with Respect to VFB∆V
Reference Voltage Line Regulation VIN = 2.65V to 10V (Note 4) 0.05 0.25 %/V

FB

Output Voltage Load Regulation Measured in Servo Loop, V

Input Voltage Range ● 2.65 10 V
Input DC Bias Current (Note 5)

Pulse Skipping Mode 2.65V < V
Burst Mode Operation V
Shutdown V

SYNC Capture Range 350 750 kHz
Oscillator Frequency VFB ≥ 0.7V 495 550 605 kHz

Phase Detector Output Current
Sinking Capability f
Sourcing Capability f

R

of P-Channel FET ISW = 100mA, VIN = 5V 0.35 0.45 Ω

DS(ON)

R

of N-Channel FET ISW = –100mA, VIN = 5V 0.37 0.5 Ω

DS(ON)

Peak Inductor Current VFB = 0.7V, Duty Cycle < 35%, V
SW Leakage V
SYNC/MODE Threshold ● 0.2 1.0 1.5 V
SYNC/MODE Leakage Current ±0.01 ±1 µA

= V

OVL

OVL

= VFB – V

UVL

Measured in Servo Loop, V

IN

SYNC/MODE

= 0V, VIN = 10V 0 1 µA

RUN

VFB = 0V 80 kHz

< f

PLLIN

OSC

> f

PPLIN

SOC

= 0V, V

RUN

≤ 85°C ● 0.740 0.80 0.840 V

A

– V

FB

UVL

< 10V, V
= VIN, I

OUT

= 0V or 10V, V

SW

= 0.9V to 1.2V ● 0.1 0.6 %

ITH

= 1.6V to 1.2V ● –0.1 –0.6 %

ITH

SYNC/MODE

= 0V, I

= 0A 15 22 µA

OUT

= 5V 1.8 2.2 2.7 A

IN

= 10V ±0.01 ±2.5 µA

IN

● 20 60 110 mV

● 20 60 110 mV

= 0A 270 365 µA

● 3 10 20 µA

● –3 –10 –20 µA

2

1879f

LTC1879

INPUT VOLTAGE (V)

2

0

R

DS(ON)

(Ω)

0.1

0.2

0.3

0.4

46

8

10

1879 G06

0.5

0.6

35

7

9

SYNCHRONOUS
SWITCH

MAIN

SWITCH

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 5V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

RUN

I

RUN

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

Note 2: The LTC1879E is guaranteed to meet specified performance from
0°C to 70°C. Specifications over the –40°C to 85°C operating ambient
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: T
dissipation P

LTC1879: TJ = TA + (PD × 140°C/W)

RUN Threshold V
RUN Input Current V

is calculated from the ambient temperature T

J

according to the following formula:

D

Ramping Up ● 0.2 0.7 1.5 V

RUN

= 0V ±0.01 ±1 µA

RUN

Note 4: The LTC1879 is tested in a feedback loop which servos V
balance point for the error amplifier (V

= 1.2V)

ITH

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

Note 6: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction

and power

A

temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.

FB

to the

UW

TYPICAL PERFOR A CE CHARACTERISTICS

R

vs Temperature

DS(ON)

0.7

0.6

0.5

0.4

(Ω)

0.3

DS(ON)

R

0.2

0.1

0

SYNCHRONOUS SWITCH
MAIN SWITCH

VIN = 5V

VIN = 10V

VIN = 10V

–50 –25 0 25 50 75 100 125

TEMPERATURE (°C)

VIN = 5V

DC Supply Current
vs Temperature

300

VIN = 5V

250

200

150

PULSE SKIPPING MODE

1879 G01

Oscillator Frequency
vs Temperature

595

VIN = 5V

575

555

535

FREQUENCY (kHz)

515

495

–50 –25 0 25 50 75 100 125

TEMPERATURE (°C)

DC Supply Current
vs Input Voltage

300

250

200

150

PULSE SKIPPING MODE

1879 G02

Oscillator Frequency
vs Supply Voltage

600
590
580
570
560
550
540
530
520

OSCILLATOR FREQUENCY (kHz)

510
500

2 4 6810

R

SUPPLY VOLTAGE (V)

vs Input Voltage

DS(ON)

1879 G03

SUPPLY CURRENT (µA)

100

50

0

–50

0 50 100 125

TEMPERATURE (°C)

Burst Mode OPERATON

1879 G04

100

DC SUPPLY CURRENT (µA)

50

0

0

Burst Mode OPERATION

2468

INPUT VOLTAGE (V)

1879 G05

10

1879f

3

LTC1879

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Leakage vs Temperature

20

VIN = 10V

18
16
14
12
10

8
6

SWITCH LEAKAGE (µA)

4
2
0

–50

0

–25

TEMPERATURE (°C)

MAIN SWITCH

SYNCHRONOUS

SWITCH

50

25

75

Reference Voltage
vs Temperature

804

VIN = 6V

803
802
801
800
799
798
797

REFERENCE VOLTAGE (mV)

796
795
794

–50 –25 0 25 50 75 100 125

TEMPERATURE (°C)

100

1879 G07

1879 G10

125

Switch Leakage vs Input Voltage Output Voltage vs Load Current

50

RUN = 0V

45

= 25°C

T

A

40
35
30
25
20
15

SWITCH LEAKAGE (nA)

10

5
0

2

0

MAIN SWITCH

SYNCHRONOUS SWITCH

4

INPUT VOLTAGE (V)

Efficiency vs Output Current

100

90

VIN = 3.6V

80

70

60

EFFICIENCY (%)

50

40

30

0.1 10 100

VIN = 5V

VIN = 7.2V

VIN = 10V

V

OUT

L = 6.2µH
Burst Mode OPERATION

1 1000

OUTPUT CURRENT (mA)

6

= 1.8V

8

10

1879 G08

1879 G11

2.51

2.50

2.49

2.48

2.47

2.46

2.45

2.44

OUTPUT VOLTAGE (V)

2.43

PULSE SKIPPING MODE
V

= 5V

2.42

IN

L = 6.2µH

2.41
0

200 600

400

800

LOAD CURRENT (mA)

Efficiency vs Output Current

100

VIN = 3.6V

90

80

70

60

EFFICIENCY (%)

50

40

30

0.1 10 100

VIN = 5V

VIN = 7.2V

VIN = 10V

V

OUT

L = 6.2µH
Burst Mode OPERATION

1 1000

OUTPUT CURRENT (mA)

1000

= 2.5V

1200

1400

1600

1879 G09

1879 G12

4

Efficiency vs Output Current

100

VIN = 7.2V

90
80
70
60
50
40

EFFICIENCY (%)

30
20
10

0

0.1 10 100

VIN = 4.2V

VIN = 4.2V

VIN = 7.2V

V

OUT

L = 6.2µH
Burst Mode OPERATION
PULSE SKIPPING MODE

1 1000

OUTPUT CURRENT (mA)

= 3.1V

1879 G13

Efficiency vs Input Voltage

100

90

80

70

60

EFFICIENCY (%)

50

V

40

L = 6.2µH
Burst Mode OPERATION

30

2

100mA 10mA

1mA

= 2.5V

OUT

46 10

INPUT VOLTAGE (V)

0.1mA

8

1879 G14

1879f

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Load Step

Load Step (Burst Mode Operation)

I

L

1A/DIV

(Pulse Skipping Mode)

I

L

1A/DIV

I

VIN

500mA/DIV

LTC1879

Soft-Start with Shorted Output

V

OUT

100mV/DIV

VIN = 5V CIN = 20µF

= 2.5V C

V

OUT

L = 4.7µHI

200mA/DIV

V

OUT

50mV/DIV

SW

5V/DIV

50µs/DIV

= 47µF

OUT

= 50mA to 1200mA

LOAD

I

L

VIN = 5V CIN = 20µF

= 2.5V C

V

OUT

L = 4.7µHI

OUT

LOAD

25µs/DIV

= 47µF

= 15mA

1879 G15

V

OUT

100mV/DIV

1879 G18

VIN = 5V CIN = 20µF

= 2.5V C

V

OUT

L = 4.7µHI

50µs/DIV

= 47µF

OUT

= 50mA to 1200mA

LOAD

200mA/DIV

V

OUT

20mV/DIV

SW

5V/DIV

RUN/SS

1V/DIV

1879 G16

Pulse Skipping Mode OperationBurst Mode Operation

I

L

VIN = 5V CIN = 20µF
V

= 2.5V C

OUT

L = 4.7µHI

VIN = 5V CIN = 20µF

= 0V C

V

OUT

L = 4.7µHI

2.5µs/DIV

= 47µF

OUT

= 15mA

LOAD

OUT

LOAD

5ms/DIV

= 47µF

= 0A

1879 G17

1879 G19

1879f

5

LTC1879

U

UU

PI FU CTIO S

SGND (Pin 1): Signal Ground Pin.
RUN/SS (Pin 2): Combination of Soft-Start and Run

Control Inputs. Forcing this pin below 0.7V shuts down the
device. In shutdown all functions are disabled and device
draws zero supply current. For the proper operation of the
part, force this pin above 2.5V. Do not leave this pin
floating. Soft-start can be accomplished by raising the
voltage on this pin gradually with an RC circuit.

VFB (Pin 3): Feedback Pin. Receives the feedback voltage
from an external resistor divider across the output.

ITH (Pin 4): Error Amplifier Compensation Point. The
current output increases with this control voltage. Nomi­nal voltage range for this pin is 0.5V to 1.8V.

SWP1, SWP2 (Pins 5, 12): Upper Switch Nodes. These
pins connect to the drains of the internal main PMOS
switches and should always be connected together
externally.

SWN1, SWN2 (Pins 6, 11): Lower Switch Nodes. These
pins connect to the drains of the internal synchronous
NMOS switches and should always be connected together
externally.

PV

, PV

IN1

Internal Drivers and Switches. These pins should always
be tied together.

SVIN (Pin 13): Signal Power Supply Pin.
PGOOD (Pin 14): Power Good Indicator Pin. Power good

is an open-drain logic output. The PGOOD pin is pulled to
ground when the voltage on the VFB pin is not within
±7.5% of its nominally regulated potential. This pin re­quires a pull-up resistor for power good indication. Power
good indication works in all modes of operation.

SYNC/MODE (Pin 15): External Clock Synchronization
and Mode Select Input. To synchronize, apply an external
clock with a frequency between 350kHz and 750kHz. To
select Burst Mode operation, tie pin to SVIN. Grounding
this pin selects pulse skipping mode. Do not leave this pin
floating.

PLL_LPF (Pin 16): Output of the Phase Detector and
Control Input of Oscillator. Connect a series RC lowpass
network from this pin to ground if externally synchronized.
If unused, this pin may be left open.

(Pins 8, 9): Power Supply Pins for the

IN2

PGND1, PGND2 (Pins 7, 10): Power Ground Pins. Ground

pins for the internal drivers and switches. These pins
should always be tied together.

6

1879f