LINEAR TECHNOLOGY LTC3252 Technical data

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FEATURES

LTC3252

Dual, Low Noise,

Inductorless Step-Down

DC/DC Converter

U

DESCRIPTIO

■

2.7V to 5.5V Input Voltage Range

■

No Inductors

■

Typical Efficiency 50% Higher than LDOs

■

Spread Spectrum Operation

■

Low Input and Output Noise

■

Shutdown Disconnects Load from V

■

Dual Adjustable Independent Outputs

IN

(Range: 0.9V to 1.6V)

■

Output Current: 250mA Each Output

■

Low Operating Current: IIN = 60µA Typ
(35µA with One Output Enabled)

■

Low Shutdown Current: IIN = 0.01µA Typ

■

Soft-Start Limits Inrush Current at Turn On

■

Short Circuit and Over Temperature Protected

■

Available in 4mm × 3mm 12-Pin DFN Package

U

APPLICATIO S

■

Handheld Electronic Devices

■

Cellular Phones

■

Low Voltage Logic Supplies

■

DSP Power Supplies

■

3.3V to 1.5V Conversion

The LTC®3252 is a switched capacitor step-down DC/DC
converter that produces two adjustable regulated outputs
from a single 2.7V to 5.5V input. The part uses switched
capacitor fractional conversion to achieve a typical effi­ciency increase of 50% over that of a linear regulator. No
inductors are required.

A unique constant frequency, spread spectrum architec­ture provides a very low noise regulated output as well as
low noise at the input. The part also has Burst Mode

®

operation to provide high efficiency at low output currents,
as well as ultralow current shutdown.

Low operating currents (60µA with both outputs enabled,
35µA with one output enabled) and low external parts
count make the LTC3252 ideally suited for space-con­strained battery-powered applications. The part is short­circuit and overtemperature protected and is available in a
tiny 4mm × 3mm 12-pin DFN package.

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

Burst Mode is a registered trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

1.5V and 1.2V Output Voltages with Shutdown

2

1µF

1µF

EN1

11

EN2

3

V

IN

4

+

C1

6

–

C1

10

+

C2

8

–

C2

7

GND

1-CELL

Li-ION

OR 3-CELL

NiMH

OFF ON
OFF ON

4.7µF

U

LTC3252

OUT1

FB1

OUT2

FB2

1.5V/1.2V Efficiency vs Input Voltage

5

470k

1

510k

9

261k

12

510k

V
I

OUT

4.7µF

V
I

OUT

4.7µF

= 1.5V

OUT

≤ 250mA

= 1.2V

OUT

≤ 250mA

3252 TA01

100

90
80
70
60

LTC3252-1.2V
50
40

EFFICIENCY (%)

30
20
10

0

3.1 3.5 3.9 4.3 4.7 5.1 5.5

2.7

I

(1.5V) = 100mA

OUT

(1.2V) = 100mA

I

OUT

LTC3252-1.5V

LDO-1.5V

LDO-1.2V

VIN (V)

3252 TA01a

3252f

1

LTC3252

FB2
EN2
C2

+

OUT2
C2

–

GND

FB1

EN1

V

IN

C1

+

OUT1

C1

–

TOP VIEW

DE PACKAGE

12-LEAD (4mm × 3mm) PLASTIC DFN

12
11
10

9
8
7

1
2
3
4
5
6

WW

W

ABSOLUTE AXI U RATI GS

U

PACKAGE/ORDER I FOR ATIO

(Notes 1, 6)

VIN to GND................................................–0.3V to 6.0V

EN1, EN2, FB1, FB2 to GND .......... –0.3V to (VIN + 0.3V)

I

, I

OUT1

(Note 3)........................................... 400mA

OUT2

Operating Ambient Temperature Range

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

Storage Temperature Range ................. –65°C to 125°C

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

T

JMAX

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

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, V

4.7µF (all capacitors ceramic) unless otherwise noted.

The ● denotes the specifications which apply over the full operating

EXPOSED PAD IS GROUND

(MUST BE SOLDERED TO PCB)

= 125°C, θJA = 40°C/W, θJC = 4.3°C/W

OUT1

= V

= 1.5V, C1 = C2 = 1µF, Cin = C

OUT2

UUW

ORDER PART

NUMBER

LTC3252EDE

DE PART

MARKING

3252

OUT1

= C

OUT2

=

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IN

Min Operating Voltage (Note 4) ● 2.7 V
Max Operating Voltage ● 5.5 V

I

VIN

Operating Current, I
Both Outputs Enabled 2.7V ≤ V

Operating Current, I
One Output Enabled V

Shutdown Current VM0 = 0V, VM1 = 0V, 2.7V ≤ VIN ≤ 5.5V ● 0.01 1 µA

V

FB1

I

OUT1

I

OUT2

I

FB

V

RIPPLE

, V

Feedback Voltage I

FB2

Output Current V
Output Current V
FB1, FB2 Input Current V
Output Ripple (OUT1 or OUT2) I
Spread Spectrum Frequency Range f

V

IH

V

IL

I

IH

I

IL

t

ON

OUT1, OUT2 Load Regulation (Referred to FB pin) 0.08 mV/mA

R

OL

2

EN1, EN2 Input High Voltage 2.7V ≤ VIN ≤ 5.5V ● 1.2 0.8 V
EN1, EN2 Input Low Voltage 2.7V ≤ VIN ≤ 5.5V ● 0.8 0.4 V
EN1, EN2 Input High Current EN1 = VIN, EN2 = V
EN1, EN2 Input Low Current EN1 = 0V, EN2 = 0V ● –1 1 µA
Turn On Time R

Line Regulation 0 ≤ I
Open Loop Output Impedance, VIN = 3.0V, I

(OUT1 or OUT2)

= 0mA, V

OUT

= 0mA, V

OUT

= 0, 2.7V ≤ V

EN2

= 0mA, 2.7V ≤ V

OUT

= V

EN1

= V

EN2

= V

FB1

FB2

= 250mA 10 mV

OUT

Switching Frequency ● 0.8 1.0 MHz

MIN

Switching Frequency ● 1.6 2.0 MHz

f

MAX

= 3Ω 0.8 ms

OUT

OUT1

IN

IN

IN

EN1

≤ 5.5V

EN1

= VIN, V

= 0, V

IN

= VIN, ● 60 100 µA

EN2

= VIN or V

EN2

= VIN, ● 35 60 µA

EN1

≤ 5.5V

≤ 5.5V ● 0.78 0.8 0.82 V

IN

● 250 mA

● 250 mA

= 0.85V ● –50 50 nA

IN

≤ 250mA or 0 ≤ I

= 200mA, VFB = 0.74V (Note 5) ● 1 1.4 Ω

OUT

≤ 250mA 0.2 %/V

OUT2

● –1 1 µA

P-P

3252f

ELECTRICAL CHARACTERISTICS

LTC3252

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

Note 2: The LTC3252EDE is guaranteed to meet specified performance
from 0°C to 70°C. Specifications over the –40°C and 85°C operating
temperature range are assured by design characterization and correlation
with statistical process control.

Note 3: Based on long-term current density limitations.

Note 4: Minimum operating voltage required for regulation is:

> 2 • (V

V

IN

Note 5: Output not in regulation; R
Note 6: This IC includes overtemperature protection that is intended to

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

UW

TYPICAL PERFOR A CE CHARACTERISTICS

No Load Supply Current vs Supply
Voltage (One Output Enabled)

60

50

40

30

(µA)

IN

I

20

10

0

2.7

85°C

–45°C

3.7 4.2 4.7

3.2

25°C

VIN (V)

5.2

3252 G01

No Load Supply Current vs Supply
Voltage (Both Outputs Enabled)

100

90
80
70
60

(µA)

50

CC

I

40
30
20
10

0

2.7

85°C

–40°C

3.7 4.2 4.7

3.2

25°C

VIN (V)

OUT(MIN)

5.2

3252 G02

+ ROL • I

0.82

0.81

0.80

(V)

0.79

FB

V

0.78

0.77

0.76

)

OUT

= (VIN/2 – V

OL

OUT

)/I

OUT

.

FB Voltage vs Load Current

VIN = 3.6V

25°C

–40°C

85°C

50 100 150 200 250

0

I

(mA)

OUT

3252 G03

EN1/EN2 Input Threshold Voltage
vs Supply Voltage

1.2

1.1

25°C

VIN (V)

(V)

SHDN

V

1.0

0.9

0.8

0.7

0.6

0.5

0.4

2.7

–40°C

85°C

3.7 4.2 4.7

3.2

5.2

3252 G04

1.5V Output Voltage vs Supply
Voltage

1.60
TA = 25°C

1.58

1.56

1.54

I

(V)

OUT

V

1.52

1.50

1.48

1.46

1.44

1.42

1.40

3

= 0mA

OUT

I

= 250mA

OUT

3.5 4 4.5 5 5.5
VIN (V)

I

OUT

= 50mA

3252 G05

1.5V Output Efficiency vs Output
Current

100

= 25°C

T

A

80

60

I

OUT

VIN = 3.1V
V
V
V
V

(mA)

= 3.3V

IN

= 3.6V

IN

= 4V

IN

= 5V

IN

40

EFFICIENCY (%)

20

0

0.1

1 10 100 1000

3252 G06

3252f

3

LTC3252

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Oscillator Max/Min Frequency vs
Supply Voltage

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

FREQUENCY (MHz)

1.1

1.0

0.9

0.8

2.7

–40°C MAX

3.2

–40°C MIN

25°C MAX

85°C MAX

25°C MIN

85°C MIN

3.7 4.2 4.7
VIN (V)

Output Current Transient
Response

250mA

I

OUT

20mA

V

OUT

20mV/DIV

AC

5.2

3252 G07

1.2V Output Voltage vs Supply
Voltage 1.2V Efficiency vs Load Current

100

TA = 25°C

80

60

40

EFFICIENCY (%)

20

0

0.1

VIN = 2.8V
V
V
V

1 10 100 1000

I

(mA)

OUT

(V)

OUT

V

1.30

1.28

1.26

1.24

1.22

1.20

1.18

1.16

1.14

1.12

1.10

2.7

TA = 25°C

3.2

I

= 0mA

OUT

I

= 50mA

OUT

I

= 250mA

OUT

3.7 4.2 4.7
VIN (V)

5.2

3252 G08

Line Transient Response

4.5V

V

IN

3.5V

V

OUT

10mV/DIV

AC

= 3.1V

IN

= 3.5V

IN

= 4.5V

IN

3252 G09

VIN = 3.6V
V

= 1.5V

OUT

3252 G11

UUU

PI FU CTIO S

FB1 (Pin 1): Feedback Input Pin 1. An output divider
should be connected from OUT1 to FB1 to program the
output voltage.

EN1 (Pin 2): Input Enable Pin 1. When EN1 is high, OUT1
is enabled. When EN1 is low OUT1 is shut down.

VIN (Pin 3): Input Supply Voltage. Operating VIN may be
between 2.7V and 5.5V. Bypass VIN with a ≥ 4.7µF (1µF
min) low ESR ceramic capacitor to GND (CIN).

V
I

OUT

OUT

= 1.5V

= 150mA

3252 G12

C1+ (Pin 4): Flying Capacitor 1 Positive Terminal (C1).
OUT1 (Pin 5): Regulated Output Voltage 1. OUT1 is

disconnected from VIN when in shutdown. Bypass OUT1
with a low ESR ceramic capacitor to GND (CO1). See
Output Capacitor Selection section for size requirements.

C1– (Pin 6): Flying Capacitor 1 Negative Terminal (C1).
GND (Pin 7): Ground. Connect to a ground plane for best

performance.

3252f

4