LTC3252
Dual, Low Noise,
Inductorless Step-Down
DC/DC Converter
FEATURES
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DESCRIPTIO
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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
IN
Dual Adjustable Independent Outputs
(Range: 0.9V to 1.6V)
Output Current: 250mA Each Output
Low Operating Current: I
IN
= 60µA Typ
(35µA with One Output Enabled)
Low Shutdown Current: I
IN
= 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
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 effi-
ciency increase of 50% over that of a linear regulator. No
inductors are required.
A unique constant frequency, spread spectrum architec-
ture 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-con-
strained battery-powered applications. The part is short-
circuit 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.
APPLICATIO S
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Handheld Electronic Devices
Cellular Phones
Low Voltage Logic Supplies
DSP Power Supplies
3.3V to 1.5V Conversion
TYPICAL APPLICATIO
2
11
3
4.7µF
4
1µF 6
10
1µF 8
7
1.5V and 1.2V Output Voltages with Shutdown
OFF ON
OFF ON
1-CELL
Li-ION
OR 3-CELL
NiMH
EN1
EN2
V
IN
C1
+
C1
–
C2
+
C2
–
GND
FB2
12
510k
3252 TA01
1.5V/1.2V Efficiency vs Input Voltage
100
V
OUT
= 1.5V
I
OUT
≤
250mA
OUT1
5
470k
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
2.7
3.1
3.5
LTC3252-1.2V
FB1
LTC3252
OUT2
1
510k
9
261k
4.7µF
V
OUT
= 1.2V
I
OUT
≤
250mA
4.7µF
U
I
OUT
(1.5V) = 100mA
I
OUT
(1.2V) = 100mA
LTC3252-1.5V
LDO-1.5V
LDO-1.2V
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
3252 TA01a
U
U
3252f
1
LTC3252
ABSOLUTE
(Notes 1, 6)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
FB1
EN1
V
IN
C1
+
OUT1
C1
–
1
2
3
4
5
6
12 FB2
11 EN2
10 C2
+
9
8
7
OUT2
C2
–
GND
V
IN
to GND ................................................– 0.3V to 6.0V
EN1, EN2, FB1, FB2 to GND .......... – 0.3V to (V
IN
+ 0.3V)
I
OUT1
, I
OUT2
(Note 3) ........................................... 400mA
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
ORDER PART
NUMBER
LTC3252EDE
DE PACKAGE
12-LEAD (4mm
×
3mm) PLASTIC DFN
EXPOSED PAD IS GROUND
(MUST BE SOLDERED TO PCB)
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 4.3°C/W
DE PART
MARKING
3252
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, V
OUT1
= V
OUT2
= 1.5V, C1 = C2 = 1µF, Cin = C
OUT1
= C
OUT2
=
4.7µF (all capacitors ceramic) unless otherwise noted.
SYMBOL
V
IN
I
VIN
PARAMETER
Min Operating Voltage
Max Operating Voltage
Operating Current,
Both Outputs Enabled
Operating Current,
One Output Enabled
Shutdown Current
V
FB1
, V
FB2
I
OUT1
I
OUT2
I
FB
V
RIPPLE
Feedback Voltage
Output Current
Output Current
FB1, FB2 Input Current
Output Ripple (OUT1 or OUT2)
Spread Spectrum Frequency Range
V
IH
V
IL
I
IH
I
IL
t
ON
EN1, EN2 Input High Voltage
EN1, EN2 Input Low Voltage
EN1, EN2 Input High Current
EN1, EN2 Input Low Current
Turn On Time
Line Regulation
R
OL
Open Loop Output Impedance,
(OUT1 or OUT2)
I
OUT
= 0mA, V
EN1
= V
IN
, V
EN2
= V
IN
,
2.7V
≤
V
IN
≤
5.5V
I
OUT
= 0mA, V
EN1
= 0, V
EN2
= V
IN
or V
EN1
= V
IN
,
V
EN2
= 0, 2.7V
≤
V
IN
≤
5.5V
V
M0
= 0V, V
M1
= 0V, 2.7V
≤
V
IN
≤
5.5V
I
OUT
= 0mA, 2.7V
≤
V
IN
≤
5.5V
V
EN1
= V
IN
V
EN2
= V
IN
V
FB1
= V
FB2
= 0.85V
I
OUT
= 250mA
f
MIN
Switching Frequency
f
MAX
Switching Frequency
2.7V
≤
V
IN
≤
5.5V
2.7V
≤
V
IN
≤
5.5V
EN1 = V
IN
, EN2 = V
IN
EN1 = 0V, EN2 = 0V
R
OUT
= 3Ω
0
≤
I
OUT1
≤
250mA or 0
≤
I
OUT2
≤
250mA
V
IN
= 3.0V, I
OUT
= 200mA, V
FB
= 0.74V (Note 5)
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
(Note 4)
q
q
q
q
q
q
q
q
q
MIN
2.7
TYP
MAX
5.5
UNITS
V
V
µA
µA
µA
V
mA
mA
60
35
0.01
0.78
250
250
– 50
10
0.8
1.2
–1
–1
0.8
0.08
0.2
1
1.0
1.6
0.8
0.8
0.8
100
60
1
0.82
50
mV
P-P
2.0
0.4
1
1
MHz
MHz
V
V
µA
µA
ms
mV/mA
%/V
1.4
Ω
OUT1, OUT2 Load Regulation (Referred to FB pin)
2
U
nA
3252f
W
U
U
W W
W
LTC3252
ELECTRICAL CHARACTERISTICS
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:
V
IN
> 2 • (V
OUT(MIN)
+ R
OL
• I
OUT
)
Note 5:
Output not in regulation; R
OL
= (V
IN
/2 – V
OUT
)/I
OUT
.
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.
TYPICAL PERFOR A CE CHARACTERISTICS
No Load Supply Current vs Supply
Voltage (One Output Enabled)
60
50
25°C
40
I
IN
(µA)
30
20
10
0
85°C
I
CC
(µA)
100
90
80
70
60
50
40
30
20
10
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3252 G01
V
FB
(V)
–45°C
EN1/EN2 Input Threshold Voltage
vs Supply Voltage
1.2
1.1
1.0
V
SHDN
(V)
0.9
0.8
0.7
0.6
1.44
0.5
0.4
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3252 G04
25°C
–40°C
V
OUT
(V)
1.52
1.50
1.48
1.46
I
OUT
= 0mA
EFFICIENCY (%)
85°C
U W
No Load Supply Current vs Supply
Voltage (Both Outputs Enabled)
0.82
FB Voltage vs Load Current
V
IN
= 3.6V
0.81
25°C
85°C
0.80
25°C
0.79
0.78
85°C
0.77
0.76
–40°C
–40°C
0
2.7
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3252 G02
0
50
100
150
I
OUT
(mA)
200
250
3252 G03
1.5V Output Voltage vs Supply
Voltage
1.60
1.58
1.56
1.54
I
OUT
= 50mA
T
A
= 25°C
80
100
1.5V Output Efficiency vs Output
Current
T
A
= 25°C
60
V
IN
= 3.1V
V
IN
= 3.3V
V
IN
= 3.6V
20
V
IN
= 4V
V
IN
= 5V
40
I
OUT
= 250mA
1.42
1.40
3
3.5
4
V
IN
(V)
3252 G05
4.5
5
5.5
0
0.1
1
10
I
OUT
(mA)
100
1000
3252 G06
3252f
3
LTC3252
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Max/Min Frequency vs
Supply Voltage
2.0
1.9
1.8
1.7
FREQUENCY (MHz)
1.6
1.4
1.3
1.2
1.1
1.0
0.9
0.8
2.7
3.2
3.7
85°C MIN
4.2
V
IN
(V)
4.7
5.2
3252 G07
–40°C MAX
25°C MAX
V
OUT
(V)
1.5
85°C MAX
1.22
1.20
1.18
1.16
1.14
1.12
1.10
2.7
I
OUT
= 0mA
I
OUT
= 50mA
I
OUT
= 250mA
EFFICIENCY (%)
25°C MIN
–40°C MIN
Output Current Transient
Response
250mA
20mA
V
IN
4.5V
3.5V
I
OUT
V
OUT
20mV/DIV
AC
V
IN
= 3.6V
V
OUT
= 1.5V
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.
V
IN
(Pin 3):
Input Supply Voltage. Operating V
IN
may be
between 2.7V and 5.5V. Bypass V
IN
with a
≥
4.7µF (1µF
min) low ESR ceramic capacitor to GND (C
IN
).
C1
+
(Pin 4):
Flying Capacitor 1 Positive Terminal (C1).
OUT1 (Pin 5):
Regulated Output Voltage 1. OUT1 is
disconnected from V
IN
when in shutdown. Bypass OUT1
with a low ESR ceramic capacitor to GND (C
O1
). 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.
4
U W
1.2V Output Voltage vs Supply
Voltage
1.30
1.28
1.26
1.24
T
A
= 25°C
80
100
1.2V Efficiency vs Load Current
T
A
= 25°C
60
40
V
IN
= 2.8V
20
V
IN
= 3.1V
V
IN
= 3.5V
V
IN
= 4.5V
3.2
3.7
4.2
V
IN
(V)
4.7
5.2
3252 G08
0
0.1
1
10
I
OUT
(mA)
100
1000
3252 G09
Line Transient Response
V
OUT
10mV/DIV
AC
3252 G11
V
OUT
= 1.5V
I
OUT
= 150mA
3252 G12
U
U
U
3252f
LTC3252
PI FU CTIO S
C2
–
(Pin 8):
Flying Capacitor 2 Negative Terminal (C2).
OUT2 (Pin 9):
Regulated Output Voltage 2. OUT2 is
disconnected from V
IN
when in shutdown. Bypass OUT2
with a low ESR ceramic capacitor to GND (C
O2
). See
Output Capacitor Selection section for size requirements.
C2
+
(Pin 10):
Flying Capacitor 2 Positive Terminal (C2).
EN2 (Pin 11):
Input Enable Pin 2. When EN2 is high, OUT2
is enabled. When EN2 is low OUT2 is shut down.
FB2 (Pin 12):
Feedback Input Pin 2. An output divider
should be connected from OUT2 to FB2 to program the
output voltage.
SI PLIFIED BLOCK DIGRAM
OVERTEMPERATURE
V
IN
3
BURST
DETECT
CIRCUIT
W
U
U
W
U
EN1
2
EN2
11
SWITCH
CONTROL
SPREAD SPECTRUM
OSCILLATOR
CHARGE
PUMP 1
4 C1
+
5 OUT1
6 C1
–
–
+
CHARGE
PUMP 2
1 FB1
10 C2
+
9 OUT2
8 C2
–
–
+
12 FB2
7
GND
3252 SBD
3252f
5
51单片机
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