LINER LTC3221EDC Micropower, regulated charge pump in 2 ã 2 dfn Datasheet

LTC3221/
LTC3221-3.3/LTC3221-5
Micropower,
Regulated Charge Pump
in 2 × 2 DFN
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FEATURES
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DESCRIPTIO
Ultralow Power: 8µA Quiescent Current
Regulated Output Voltages: 3.3V ±4%, 5V ±4%, ADJ
VIN Range:
1.8V to 4.4V (LTC3221-3.3)
2.7V to 5.5V (LTC3221-5)
Output Current: Up to 60mA
No Inductors Needed
Very Low Shutdown Current: <1µA
Shutdown Disconnects Load from VIN
Burst Mode Control
Short-Circuit Protected
Solution Profile < 1mm
Tiny 2mm × 2mm 6-Pin DFN Package
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APPLICATIO S
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Low Power 2 AA Cell to 3.3V Supply
Memory Backup Supplies
Tire Pressure Sensors
General Purpose Low Power Li-Ion to 5V Supply
RF Transmitters
Glucose Meters
The LTC3221 family includes fixed 5V and 3.3V output
versions plus an adjustable version. All parts operate
as Burst Mode® switched capacitor voltage doublers
to achieve ultralow quiescent current. The chips use a
controlled current to supply the output and will survive
a continuous short-circuit from VOUT to GND. The FB pin
of the adjustable LTC3221 can be used to program the
desired output voltage.
The LTC3221 family is available in a low profile (0.75mm)
2mm × 2mm 6-pin DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst
Mode is a registered trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
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The LTC®3221 family are micropower charge pump DC/DC
converters that produce a regulated output at up to 60mA.
The input voltage range is 1.8V to 5.5V. Extremely low
operating current (8µA typical at no load) and low external
parts count (one flying capacitor and two small bypass
capacitors at VIN and VOUT) make them ideally suited for
small, battery-powered applications.
TYPICAL APPLICATIO
No-Load Input Current
vs Supply Voltage
1µF
16
VIN
5
2.2µF
4,7
OFF ON
3
C–
VIN
1
C+
6
VOUT
VOUT
4.7µF
LTC3221-X
GND
SHDN
3221 TA01
REGULATED 3.3V OUTPUT FROM 1.8V TO 4.4V INPUT
VOUT = 3.3V ±4%
IOUT = OmA TO 25mA; VIN >1.8V
IOUT = OmA TO 60mA; VIN >2V
REGULATED 5V OUTPUT FROM 2.7V TO 5.5V INPUT
VOUT = 5V ±4%
IOUT = OmA TO 25mA; VIN >2.7V
IOUT = OmA TO 60mA; VIN >3V
NO-LOAD INPUT CURRENT (µA)
2
14
12
10
8
6
TA = 90°C
TA = 25°C
TA = –45°C
4
2
0
1.5
2.0
2.5
3.0
3.5
SUPPLY VOLTAGE (V)
4.0
4.5
3221 TA01b
3221f
1
LTC3221/
LTC3221-3.3/LTC3221-5
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
VIN, ⎯S⎯H⎯D⎯N, FB ............................................. – 0.3V to 6V
VOUT to GND............................................. – 0.3V to 5.5V
VOUT Short-Circuit Duration ............................ Indefinite
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range.................. – 65°C to 125°C
Maximum Junction Temperature .......................... 125°C
C+ 1
C– 2
6 VOUT
7
SHDN/FB* 3
5 VIN
4 GND
TJMAX = 125°C, θJA = 80°C/W
EXPOSED PAD IS GND (PIN 7) MUST BE SOLDERED TO PCB
*⎯S⎯H⎯D⎯N ON LTC3221-3.3;LTC3221-5 FB ON LTC3221
ORDER PART NUMBER
DC PART MARKING
LTC3221EDC
LTC3221EDC-3.3
LTC3221EDC-5
LCCP
LBQP
LCCN
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
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 2.5V (LTC3221-3.3/LTC3221) or 3V (LTC3221-5), ⎯S⎯H⎯D⎯N = VIN,
CFLY = 1µF, CIN = 2.2µF, COUT = 2.2µF, unless otherwise specified.
SYMBOL
LTC3221-3.3
PARAMETER
CONDITIONS
VIN
Input Supply Voltage
VOUT
Output Voltage
ICC
Operating Supply Current
VR
Output Ripple
VIN = 2V, IOUT = 60mA, COUT = 4.7µF (Note 3)
35
mVP-P
η
Efficiency
VIN = 2V, IOUT = 60mA (Note 3)
82
%
ISC
Output Short-Circuit Current
VOUT = 0V
1.8V ≤ VIN ≤ 4.4V, IOUT ≤ 25mA
2V ≤ VIN < 4.4V, IOUT ≤ 60mA
IOUT = 0mA
MIN
●
1.8
●
3.168
●
●
TYP
3.3
8
120
MAX
UNITS
4.4
V
3.432
15
V
µA
240
mA
5.5
V
5.2
15
V
µA
LTC3221-5
VIN
Input Supply Voltage
VOUT
Output Voltage
ICC
Operating Supply Current
2.7V ≤ VIN ≤ 5.5V, IOUT < 25mA
3V ≤ VIN ≤ 5.5V, IOUT < 60mA
IOUT = 0mA
VR
Output Ripple
VIN = 3V, IOUT = 60mA, COUT = 4.7µF (Note 3)
η
Efficiency
VIN = 3V, IOUT = 60mA (Note 3)
ISC
Output Short-Circuit Current
VOUT = 0V
●
2.7
●
4.8
●
5
8
45
mVP-P
82
●
120
%
240
mA
5.5
V
LTC3221
●
1.8
●
1.181
VIN
Input Supply Voltage
VFB
Feedback Voltage
ROL
Open-Loop Impedance
VIN = 1.8V, VOUT = 3V (Note 4)
●
ICC
Operating Supply Current
IOUT = 0mA
●
IFB
FB Input Current
FB = 1.33V, VIN = 2V
●
1.23
1.279
V
10
20
Ω
12
µA
100
nA
5
–100
3221f
2
LTC3221/
LTC3221-3.3/LTC3221-5
ELECTRICAL
CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C. V = 2.5V (LTC3221-3.3/LTC3221) or 3V (LTC3221-5), ⎯S⎯H⎯D⎯N = V ,
A
IN
IN
CFLY = 1µF, CIN = 2.2µF, COUT = 2.2µF, unless otherwise specified.
SYMBOL
PARAMETER
LTC3221-3.3/LTC3221-5
Shutdown Supply Current
I⎯S⎯H⎯D⎯N
⎯S⎯H⎯D⎯N Input Threshold (High)
VIH
⎯S⎯H⎯D⎯N Input Threshold (Low)
VIL
⎯S⎯H⎯D⎯N Input Current (High)
IIH
⎯S⎯H⎯D⎯N Input Current (Low)
IIL
LTC3221/LTC3221-3.3/LTC3221-5
Switching Frequency
fOSC
UVLO Threshold
VUVLO
CONDITIONS
MIN
VOUT = 0V, ⎯S⎯H⎯D⎯N = 0V
TYP
●
µA
V
V
µA
µA
1.3
●
⎯S⎯H⎯D⎯N = VIN
⎯SH
⎯ D
⎯ N
⎯ = 0V
UNITS
1
●
●
0.4
1
1
–1
–1
●
VOUT = 2.5V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3221EDC-X is guaranteed to meet performance
specifications from 0°C to 70°C. Specificaiton over the –40°C to 85°C
MAX
600
1
kHz
V
operating temperature range are assured by design, characterization and
correlation with statisitical process controls.
Note 3: Guaranteed by design, not subject to test.
Note 4: ROL = (2VIN – VOUT)/IOUT.
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TYPICAL PERFOR A CE CHARACTERISTICS
800
750
750
700
700
650
600
550
600
VIN = 2.5V
450
450
4.0
400
–50
4.5
VIN = 1.8V
550
500
2.5
3.0
3.5
SUPPLY VOLTAGE (V)
VIN = 4.5V
650
500
2.0
0.9
THRESHOLD VOLTAGE (V)
800
400
1.5
⎯S⎯H⎯D⎯N Threshold Voltage vs
Supply Voltage
Oscillator Frequency vs
Temperature
FREQUENCY (kHz)
FREQUENCY (kHz)
Oscillator Frequency vs
Supply Voltage
–25
0
25
50
75
TEMPERATURE (°C)
100
⎯S⎯H⎯D⎯N LO-to-HI Threshold vs
Temperature
VIN = 1.8V
0.5
0
25
50
75
TEMPERATURE (°C)
0.5
100
125
3221 G04
2.0
2.5
3.0
3.5
SUPPLY VOLTAGE (V)
4.5
Short-Circuit Current vs
Supply Voltage
150
VIN = 3.2V
0.8
0.7
4.0
3221 G03
SHORT-CIRCUIT CURRENT (mA)
0.6
SHDN HI-TO-LO THRESHOLD (V)
SHDN LO-TO-HI THRESHOLD (V)
VIN = 3.2V
–25
0.6
0.4
1.5
125
0.9
VIN = 2.5V
0.4
–50
HIGH-TO-LOW THRESHOLD
⎯S⎯H⎯D⎯N HI-to-LO Threshold vs
Temperature
0.9
0.7
0.7
3221 G02
3221 G01
0.8
LOW-TO-HIGH THRESHOLD
0.8
VIN = 2.5V
0.6
VIN = 1.8V
0.5
0.4
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3221 G05
TA = –45°C
130
TA = 90°C
110
TA = 25°C
90
70
50
1.5
2.0
2.5
3.0
3.5
SUPPLY VOLTAGE (V)
4.0
4.5
3221 G06
3221f
3
LTC3221/
LTC3221-3.3/LTC3221-5
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TYPICAL PERFOR A CE CHARACTERISTICS
3.36
120
3.34
110
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
VOUT = 3.168V
TA = –45°C
VIN = 3.2V
3.32
3.30
VIN = 2.5V
3.26
3.24
VIN = 1.8V
3.22
Effective Open-Loop Output
Resistance vs Temperature
100
90
TA = 90°C
80
TA = 25°C
70
60
3.20
50
3.18
3.16
0
20
40
60
80
LOAD CURRENT (mA)
100
40
1.5
120
2.0
2.5
3.0
SUPPLY VOLTAGE (V)
3.5
EFFECTIVE OPEN-LOOP OUTPUT RESISTANCE (Ω)
Output Load Capability at 4%
Below Regulation
Load Regulation
3.28
(LTC3221-3.3 only)
15
VIN = 1.8V
14 VOUT = 3V
13
12
11
10
9
8
7
6
5
–50
–25
0
25
50
TEMPERATURE (°C)
75
3221 G08
100
3221 G09
3221 G07
No-Load Input Current vs
Supply Voltage
Extra Input Current vs Load
Current (IIN-2 ILOAD)
10
16
Efficiency vs Supply Voltage
100
VIN = 2.5V
90
12
TA = 90°C
10
8
TA = 25°C
TA = –45°C
6
4
1
0.1
70
60
IOUT = 30mA
IOUT = 1mA
50
40
30
0.01
20
2
0
1.5
THEORETICAL MAX
80
EFFICIENCY (%)
EXCESS INPUT CURRENT (mA)
NO-LOAD INPUT CURRENT (µA)
14
10
2.0
2.5
3.0
3.5
SUPPLY VOLTAGE (V)
4.0
4.5
0.001
0.01
0
0.1
1
10
LOAD CURRENT (mA)
100
1.8
2.0
2.2 2.4 2.6
2.8
SUPPLY VOLTAGE (V)
3221 G10
3.2
3221 G12
3221 G11
Output Ripple vs Load Current
3.0
Output Ripple
Load Transient Response
70
VOUT
20mV/DIV
(AC-COUPLED)
OUTPUT RIPPLE (mVP-P)
60
COUT = 2.2µF
VOUT
20mV/DIV
(AC-COUPLED)
50
40
60mA
IOUT
0mA
COUT = 4.7µF
30
20
10
0
0
20
40
60
80
LOAD CURRENT (mA)
100
1µs/DIV
VIN = 2V
ILOAD = 60mA
COUT = 4.7µF, 6.3V, SIZE 0603
3221 G14
5µs/DIV
VIN = 2V
ILOAD = 0mA TO 60mA STEP
COUT = 4.7µF, 6.3V, SIZE 0603
3221 G15
3221 G13
3221f
4
LTC3221/
LTC3221-3.3/LTC3221-5
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TYPICAL PERFOR A CE CHARACTERISTICS
120
5.10
TA = –45°C
110
5.05
VIN = 4.2V
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
VOUT = 4.8V
Effective Open-Loop Output
Resistance vs Temperature
5.00
VIN = 3.6V
4.95
VIN = 2.7V
4.90
4.85
100
TA = 90°C
90
TA = 25°C
80
70
60
50
0
20
40
60
80
LOAD CURRENT (mA)
40
2.7
120
100
3.0
3.3
3.6
3.9
SUPPLY VOLTAGE (V)
4.2
EFFECTIVE OPEN-LOOP OUTPUT RESISTANCE (Ω)
Output Load Capability at 4%
Below Regulation
Load Regulation
4.80
(LTC3221-5 only)
15
VIN = 2.7V
14 VOUT = 4.5V
13
12
11
10
9
8
7
6
5
–50
–25
0
25
50
TEMPERATURE (°C)
75
3221 G17
100
3221 G18
3221 G16
No-Load Input Current vs
Supply Voltage
Extra Input Current vs Load
Current (IIN-2 ILOAD)
10
16
Efficiency vs Supply Voltage
100
VIN = 3V
90
12
10
TA = 90°C
8
TA = –45°C
6
TA = 25°C
4
80
1
EFFICIENCY (%)
EXCESS INPUT CURRENT (mA)
NO-LOAD INPUT CURRENT (µA)
14
0.1
THEORETICAL MAX
70
IOUT = 1mA
60
IOUT = 30mA
50
40
30
0.01
20
2
10
0
2.7
3.0
3.3
3.6
3.9
SUPPLY VOLTAGE (V)
4.2
4.5
0.001
0.01
0
0.1
1
10
LOAD CURRENT (mA)
100
2.7
3.0
3.3
3.6
3.9
SUPPLY VOLTAGE (V)
3221 G19
Output Ripple vs Load Current
Output Ripple
Load Transient Response
VIN = 3V
VOUT
50mV/DIV
(AC-COUPLED)
OUTPUT RIPPLE (mVP-P)
80
COUT = 2.2µF
70
4.5
3221 G21
3221 G20
90
4.2
VOUT
50mV/DIV
(AC-COUPLED)
60
50
60mA
IOUT
0mA
40
COUT = 4.7µF
30
20
10
0
0
20
60
80
40
LOAD CURRENT (mA)
100
1µs/DIV
VIN = 3V
ILOAD = 60mA
COUT = 4.7µF, 6.3V, SIZE 0603
3221 G23
5µs/DIV
VIN = 3V
ILOAD = 0mA TO 60mA STEP
COUT = 4.7µF, 6.3V, SIZE 0603
3221 G24
3221 G13
3221f
5
LTC3221/
LTC3221-3.3/LTC3221-5
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PI FU CTIO S
C+ (Pin 1): Flying Capacitor Positive Terminal.
GND (Pin 4): Ground. Should be tied to a ground plane
for best performance.
C– (Pin 2): Flying Capacitor Negative Terminal.
⎯ SH
⎯ D
⎯ N
⎯ (Pin 3) (LTC3221-3.3/LTC3221-5): Active Low
⎯ D
⎯ N
⎯ disables the LTC3221-3.3/
Shutdown Input. A low on S⎯ H
⎯ D
⎯ N
⎯ must not be allowed to float.
LTC3221-5. S⎯ H
FB (Pin 3) (LTC3221): Feedback. The voltage on this pin
is compared to the internal reference voltage (1.23V) by
the error comparator to keep the output in regulation. An
external resistor divider is required between VOUT and FB
to program the output voltage.
VIN (Pin 5): Input Supply Voltage. VIN should be bypassed
with a 2.2µF low ESR capacitor.
VOUT (Pin 6): Regulated Output Voltage. For best performance, VOUT should be bypassed with a 2.2µF or higher
low ESR capacitor as close as possible to the pin.
Exposed Pad (Pin 7) Ground. The exposed pad must be
soldered to PCB ground to provide electrical contact and
optimum thermal performance.
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BLOCK DIAGRA
LTC3221-3.3/LTC3221-5
VOUT
LTC3221
VOUT
6
2
1
CMP
+
CONTROL
–
1
C+
5
VIN
2
C–
6
2
1
ISW
CMP
FB
3
CONTROL
5
VIN
2
C–
4
GND
2
–
1
C+
ISW
+
2
1
1
VREF
4
SHDN
GND
VREF
3
3221 BD
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OPERATIO
(Refer to Block Diagrams)
The LTC3221 family uses a switched capacitor charge pump
to boost VIN to a regulated output voltage. Regulation is
achieved by monitoring the output voltage, VOUT using a
comparator (CMP in the Block Diagram) and keeping it
within a hysteresis window. If VOUT drops below the lower
trip point of CMP, VOUT is charged by the controlled current, ISW in series with the flying capacitor CFLY. Once VOUT
goes above the upper trip point of CMP, or if the upper
trip point is not reached after 0.8µs, CFLY is disconnected
from VOUT. The bottom plate of CFLY is then connected
to GND to allow ISW to replenish the charge on CFLY for
0.8µs. After which, ISW is turned off to keep the operating
supply current low. CMP continues to monitor VOUT and
turns on ISW if the lower threshold is reached again.
6
Shutdown Mode
The ⎯S⎯H⎯D⎯N pin is a CMOS input with a threshold voltage
of approximately 0.8V. The LTC3221-3.3/ LTC3221-5 are
in shutdown when a logic low is applied to the ⎯S⎯H⎯D⎯N
pin. In shutdown mode, all circuitry is turned off and the
LTC3221-3.3/ LTC3221-5 draw only leakage current from
the VIN supply. Furthermore, VOUT is disconnected from
VIN. Since the ⎯S⎯H⎯D⎯N pin is a very high impedance CMOS
input, it should never be allowed to float.
When ⎯S⎯H⎯D⎯N is asserted low, the charge pump is first disabled, but the LTC3221-3.3/LTC3221-5 continue to draw
5µA of supply current. This current will drop to zero when
the output voltage (VOUT) is fully discharged to 0V.
3221f
LTC3221/
LTC3221-3.3/LTC3221-5
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OPERATIO
(Refer to Block Diagrams)
The LTC3221 has a FB pin in place of the ⎯S⎯H⎯D⎯N pin. This
allows the output voltage to be programmed using an
external resistive divider.
VOUT stays above this lower threshold for a long period of
time, this result in a very low average input current.
Soft-Start and Short-Circuit Protection
Burst Mode Operation
The LTC3221 family regulates the output voltage throughout
the full 60mA load range using Burst Mode control. This
keeps the quiescent current low at light load and improves
the efficiency at full load by reducing the switching losses.
All the internal circuitry except the comparator is kept off
if the output voltage is high and the flying capacitor has
been fully charged. These circuits are turned on only if VOUT
drops below the comparator lower threshold. At light load,
The LTC3221 family uses a controlled current, ISW to
deliver current to the output. This helps to limit the input
and output current during start-up and output short-circuit
condition. During start up ISW is used to charge up the flying
capacitor and output capacitor, this limits the input current
to approximately 240mA. During short-circuit condition,
the output current is delivered through ISW and this limits
the output current to approximately 120mA. This prevents
excessive self-heating that causes damage to the part.
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APPLICATIO S I FOR ATIO
Power Efficiency
The input current of a doubling charge pump like the LTC3221
family is always twice that of the output current. This is
true regardless of whether the output voltage is unregulated
or regulated or of the regulation method used. In an ideal
unregulated doubling charge pump, conservation of energy
implies that the input current has to be twice that of the
output current in order to obtain an output voltage twice
that of the input voltage. In a regulated charge pump like
the LTC3221, the regulation of VOUT is similar to that of a
linear regulator, with the voltage difference between 2 • VIN
(Input voltage plus the voltage across a fully charged flying
capacitor) and VOUT being absorbed in an internal pass
transistor. In the LTC3221, the controlled current ISW acts as
a pass transistor. So the input current of an ideal regulated
doubling charge pump is the same as an unregulated one,
which is equal to twice the output current. The efficiency
(n) of an ideal regulated doubler is therefore given by:
η=
the theoretical 83.3% calculation. The LTC3221 product
family continues to maintain good efficiency even at fairly
light loads because of its inherently low power design.
Maximum Available Output Current
For the adjustable LTC3221, the maximum available output
current and voltage can be calculated from the effective
open-loop output resistance, ROL, and effective output
voltage, 2VIN(MIN).
From Figure 1 the available current is given by:
IOUT =
2VIN – VOUT
ROL
Effective Open-Loop Output Resistance (ROL)
The effective open-loop output resistance(ROL) of a charge
pump is a very important parameter which determines the
strength of the charge pump. The value of this parameter
POUT VOUT • IOUT VOUT
=
=
2VIN
PIN
VIN • 2IOUT
At moderate to high output power, the switching losses and
quiescent current of the LTC3221 family are negligible and
the expression is valid. For example, an LTC3221-5 with VIN
= 3V, IOUT = 60mA and VOUT regulating to 5V, has a measured efficiency of 82% which is in close agreement with
ROL
+
–
+
2VIN
IOUT
VOUT
–
3221 F01
Figure 1. Equivalent Open-Loop Circuit
3221f
7
LTC3221/
LTC3221-3.3/LTC3221-5
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APPLICATIO S I FOR ATIO
depends on many factors such as the oscillator frequency
(fOSC), value of the flying capacitor (CFLY), the nonoverlap
time, the internal switch resistances (RS) and the ESR of
the external capacitors. A first order approximation for
ROL is given below:
ROL ≅ 2
∑
S = 1 TO 4
RS +
1
fOSC • C FLY
EFFECTIVE OPEN-LOOP OUTPUT RESISTANCE (Ω)
Typical ROL values as a function of temperature are shown
in Figure 2.
15
VIN = 1.8V
14 VOUT = 3V
13
12
11
ESR of the output capacitor. It is proportional to the input
voltage, the value of the flying capacitor and the ESR of
the output capacitor.
A smaller output capacitor and/ or larger output current
load will result in higher ripple due to higher output voltage slew rates.
There are several ways to reduce output voltage ripple.
For applications requiring lower peak-to-peak ripple, a
larger COUT capacitor (4.7µF or greater) is recommended.
A larger capacitor will reduce both the low and high frequency ripple due to the lower charging and discharging
slew rates, as well as the lower ESR typically found with
higher value (larger case size) capacitors. A low ESR ceramic output capacitor will minimize the high frequency
ripple, but will not reduce the low frequency ripple unless
a high capacitance value is used.
10
VIN, VOUT Capacitor Selection
9
8
7
6
5
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3221 F02
Figure 2. Effective Open-Loop Output Resistance vs Temperature
Output Ripple
Low frequency regulation mode ripple exists due to the
hysteresis in the comparator CMP and propagation delay
in the charge pump control circuit. The amplitude and
frequency of this ripple are heavily dependent on the load
current, the input voltage and the output capacitor size.
The LTC3221 family uses a controlled current, ISW to deliver
current to the output. This helps to keep the output ripple
fairly constant over the full input voltage range. Typical
combined output ripple for the LTC3221-3.3 with VIN =
2V under maximum load is 35mVP-P using a 4.7µF 6.3V
X5R case size 0603 output capacitor.
A high frequency ripple component may also be present
on the output capacitor due to the charge transfer action
of the charge pump. In this case the output can display
a voltage pulse during the charging phase. This pulse
results from the product of the charging current and the
The style and value of capacitors used with the LTC3221
family determine several important parameters such as
output ripple, charge pump strength and minimum startup time.
To reduce noise and ripple, it is recommended that low
ESR (< 0.1Ω) capacitors be used for both CIN and COUT.
These capacitors should be either ceramic or tantalum
and should be 2.2µF or greater. Aluminum capacitors are
not recommended because of their high ESR.
Flying Capacitor Selection
Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitor since
its voltage can reverse upon start-up of the LTC3221.
Low ESR ceramic capacitors should always be used for
the flying capacitor.
The flying capacitor controls the strength of the charge
pump. In order to achieve the rated output current, it is
necessary to have at least 0.6µF of capacitance for the
flying capacitor. For very light load applications, the flying
capacitor may be reduced to save space or cost.From the
first order approximation of ROL in the section “Effective
Open-Loop Output Resistance,” the theoretical minimum
output resistance of a voltage doubling charge pump can
3221f
8
LTC3221/
LTC3221-3.3/LTC3221-5
U
W
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APPLICATIO S I FOR ATIO
be expressed by the following equation:
ROL(MIN) ≡
2VIN – VOUT
1
≅
IOUT
fOSC • C FLY
where fOSC is the switching frequency (600kHz) and CFLY
is the value of the flying capacitor. The charge pump will
typically be weaker than the theoretical limit due to additional switch resistance. However, for very light load applications, the above expression can be used as a guideline
in determining a starting capacitor value.
Programming the LTC3221 Output Voltage (FB Pin)
While the LTC3221-3.3/LTC3221-5 versions have internal
resistive dividers to program the output voltage, the programmable LTC3221 may be set to an arbitrary voltage via
an external resistive divider. Figure 3 shows the required
voltage divider connection.
VOUT 6
R1
LTC3221
FB
C1
COUT
3
Ceramic Capacitors
R2
Capacitors of different materials lose their capacitance
with higher temperature and voltage at different rates.
For example, a ceramic capacitor made of X7R material
will retain most of its capacitance from –40°C to 85°C,
whereas, a Z5U or Y5V style capacitor will lose considerable
capacitance over that range. Z5U and Y5V capacitors may
also have a very strong voltage coefficient causing them
to lose 50% or more of their capacitance when the rated
voltage is applied. Therefore when comparing different
capacitors, it is often more appropriate to compare the
amount of achievable capacitance for a given case size
rather than discussing the specified capacitance value.
For example, over rated voltage and temperature conditions, a 1µF 10V Y5V ceramic capacitor in a 0603 case
may not provide any more capacitance than a 0.22µF 10V
X7R capacitor available in the same 0603 case. In fact,
for most LTC3221-3.3/LTC3221-5/LTC3221 applications,
these capacitors can be considered roughly equivalent. The
capacitor manufacturer’s data sheet should be consulted
to determine what value of capacitor is needed to ensure
0.6µF at all temperatures and voltages.
Table 1 shows a list of ceramic capacitor manufacturers
and how to contact them.
Table 1. Ceramic Capacitor Manufacturers
AVX
Kemet
Murata
Taiyo Yuden
Vishay
VOUT = 1.23V (1 + R1 )
R2
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
GND
4
3221 F03
Figure 3. Programming the Adjustable LTC3221
The voltage divider ratio is given by the expression:
R1 VOUT
=
–1
R2 1.23V
Since the LTC3221 employs a voltage doubling charge
pump, it is not possible to achieve output voltages greater
than twice the available input voltage. The VIN supply
range required for regulation is given by the following
expression:
Maximum VIN < VOUT + 0.6
Minimum VIN =
( VOUT + IOUT • ROL ) or 1.8V;
2
whichever is higher
Where ROL is the effective open-loop output resistance and
IOUT is the maximum load current. VIN cannot be higher
than VOUT by more than 0.6V, or else the line regulation
is poor. Also, VIN has to be higher than the minimum
operating voltage of 1.8V.
The sum of the voltage divider resistors can be made large
to keep the quiescent current to a minimum. Any standing
current in the output divider (given by 1.23/R2) will be
reflected by a factor of 2 in the input current. A reasonable
resistance value should be such that the standing current
is in the range of 10µA to 100µA when VOUT is regulated.
3221f
9
LTC3221/
LTC3221-3.3/LTC3221-5
U
U
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APPLICATIO S I FOR ATIO
If the standing current is too low, the FB pin becomes very
sensitive to the switching noise and will result in errors in
the programmed VOUT.
The compensation capacitor (C1) helps to improve the
response time of the comparator and to keep the output
ripple within an acceptable range. For best results, C1
should be between 22pF to 220pF.
Layout Considerations
Due to high switching frequency and high transient currents produced by the LTC3221 product family, careful
board layout is necessary. A true ground plane and short
2.2µF
1µF
2
3
R1
VOUT
VIN
5
4
To prevent an overtemperature condition in high power
applications, Figure 5 should be used to determine the
maximum combination of ambient temperature and power
dissipation.
The power dissipated in the LTC3221 family should always
fall under the line shown for a given ambient temperature.
The power dissipation is given by the expression:
PD = (2V IN– VOUT )• IOUT
VOUT
6
PIN 7
Derating Power at High Temperatures
2.2µF
GND
R2
3221 F04
Figure 4. Recommended Layout
connections to all capacitors will improve performance
and ensure proper regulation under all conditions. Figure 4
shows the recommended layout configuration.
The flying capacitor pins C+ and C– will have very high
edge rate waveforms. The large dv/dt on these pins can
couple energy capacitively to adjacent printed circuit board
runs. Magnetic fields can also be generated if the flying
capacitors are not close to the LTC3221 (i.e. the loop area
is large). To decouple capacitive energy transfer, a Faraday
shield may be used. This is a grounded PC trace between
the sensitive node and the LTC3221 pins. For a high quality
AC ground it should be returned to a solid ground plane
that extends all the way to the LTC3221.
To reduce the maximum junction temperature due to
power dissipation in the chip, a good thermal connection
This derating curve assumes a maximum thermal resistance, θJA, of 80°C/W for 2mm × 2mm DFN package.
This can be achieved from a printed circuit board layout
with a solid ground plane and a good connection to the
ground pins of the LTC3221 and the Exposed Pad of the
DFN package. Operation out of this curve will cause the
junction temperature to exceed 150°C which is the maximum junction temperature allowed.
3.0
θJA = 80°C/W
TJ = 160°C
2.5
POWER DISSIPATION (W)
(LTC3221)
1
to the PC board is recommended. Connecting the GND pin
(Pin 4 and Pin 7 on the DFN package) to a ground plane,
and maintaining a solid ground plane under the device
can reduce the thermal resistance of the package and PC
board considerably.
2.0
1.5
1.0
0.5
0
–50 –25
25 50 75 100 125
0
AMBIENT TEMPERATURE (°C)
150
3221 F05
Figure 5. Maximum Power Dissipation vs Ambient Temperature
3221f
10
LTC3221/
LTC3221-3.3/LTC3221-5
U
PACKAGE DESCRIPTIO
DC Package
6-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115
TYP
0.56 ± 0.05
(2 SIDES)
0.675 ±0.05
2.50 ±0.05
1.15 ±0.05 0.61 ±0.05
(2 SIDES)
PIN 1 BAR
PACKAGE
TOP MARK
OUTLINE
(SEE NOTE 6)
0.38 ± 0.05
4
2.00 ±0.10
(4 SIDES)
PIN 1
CHAMFER OF
EXPOSED PAD
3
0.25 ± 0.05
0.50 BSC
1.42 ±0.05
(2 SIDES)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
6
1
(DC6) DFN 1103
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
1.37 ±0.05
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3221f
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.
11
LTC3221/
LTC3221-3.3/LTC3221-5
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1262
12V, 30mA Flash Memory Program Supply
Regulated 12V ±5% Output, IQ = 500µA
LTC1514/LTC1515
Buck/Boost Charge Pumps with IQ = 60µA
50mA Output at 3.3V or 5V; 2V to 10V Input
LTC1516
Micropower 5V Charge Pump
IQ = 12µA, Up to 50mA Output, VIN = 2V to 5V
LTC1517-5/LTC1517-3.3
Micropower 5V/3.3V Doubler Charge Pumps
IQ = 6µA, Up to 20mA Output
LTC1522
Micropower 5V Doubler Charge Pump
IQ = 6µA, Up to 20mA Output
LTC1555/LTC1556
SIM Card Interface
Step-Up/Step-Down Charge Pump, VIN = 2.7V to 10V
LTC1682
Low Noise Doubler Charge Pump
Output Noise = 60µVRMS, 2.5V to 5.5V Output
LTC1751-3.3/LTC1751-5
Micropower 5V/3.3V Doubler Charge Pumps
IQ = 20µA, Up to 100mA Output, SOT-23 Package
LTC1754-3.3/LTC1754-5
Micropower 5V/3.3V Doubler Charge Pumps
IQ = 13µA, Up to 50mA Output, SOT-23 Package
LTC1755
Smart Card Interface
Buck/Boost Charge Pump, IQ = 60µA, VIN = 2.7V to 6V
LTC3200
Constant Frequency Doubler Charge Pump
Low Noise, 5V Output or Adjustable
LTC3203/LTC3203B/
LTC3203B-1/LTC3203-1
500mA Low Noise High Efficiency Dual Mode
Step Up Charge Pumps
VIN: 2.7V to 5.5V, 3mm × 3mm DFN-10 Package
LTC3204/LTC3204B-3.3/
LTC3204-5
Low Noise Regulated Charge Pumps
Up to 150mA (LTC3204-5), Up to 50mA (LTC3204-3.3)
LTC3240-3.3/LTC3240-2.5
Step-Up/Step-Down Regulated Charge Pumps
Up to 150mA Output
3221f
12 Linear Technology Corporation
LT 1006 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2006
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