LTC3203-1/LTC3203B/LTC3203B-1 - 500mA Output Current Low Noise Dual Mode Step-Up Charge Pumps

LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
500mA Output Current
Low Noise Dual Mode
Step-Up Charge Pumps
DESCRIPTIO
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FEATURES
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The LTC®3203/LTC3203-1/LTC3203B/LTC3203B-1 are low
noise, high efficiency charge pump DC/DC converters
capable of driving loads up to 500mA from a 2.7V to 5.5V
input. Low external parts count (two flying capacitors and
bypass capacitors at VIN and VOUT) make the LTC3203
family ideally suited for small, battery-powered applications.
Selectable Dual Mode Operation: 1:1.5 or 1:2
High Output Current: Up to 500mA
Low Noise Constant Frequency (1MHz/0.9MHz)
Operation*
VIN Range: 2.7V to 5.5V
Adjustable Output Voltage (LTC3203/LTC3203B)
User Selectable Fixed Output Voltages: 4.5V or 5V
(LTC3203-1 and LTC3203B-1)
Burst Mode® Operation with
IQ ~ 120µA (LTC3203/LTC3203-1)
Constant Freqency Operation at All Loads
(LTC3203B/LTC3203B-1)
Soft-Start Limits Inrush Current at Turn-On
Short-Circuit/Thermal Protection
Shutdown Disconnects Load from Input
Shutdown Current: < 1µA
Available in a 10-pin (3mm × 3mm) DFN Package
Built-in soft-start circuitry prevents excessive inrush
current during start-up. High switching frequency enables
the use of small external capacitors. The LTC3203/
LTC3203-1 feature Burst Mode operation at light load to
achieve high efficiency whereas the LTC3203B/
LTC3203B-1 operate at constant frequency to achieve
lowest noise operation.
The LTC3203-1/LTC3203B-1 have a user selectable fixed
output voltage of 4.5V or 5V to power LEDs or logic
circuits. The FB pin of the LTC3203/LTC3203B can be used
to program the desired output voltage. The parts are shortcircuit and overtemperature protected and are available in
a low profile (3mm × 3mm) DFN package.
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APPLICATIO S
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High Current LED Backlight Supply for
Cellphones/PDAs
Cellphone Camera Light Supply
General Purpose 3.3V or Li-Ion to 5V Supply
USB ON THE GO(OTG) Devices
, 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.
*Protected by U.S. Patents including 6411531.
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TYPICAL APPLICATIO
Efficiency vs VIN at 300mA Load Current
100
OUTPUT PROGRAMMING
80
SHDN VSEL
LTC3203-1
VIN
2.2µF
2.2µF
R1*
VIN
VOUT
C1+
C2+
C1–
MODE
100k
C2–
VOUT
500mA
10µF
2.2µF
300mA
300mA
500mA
500mA
LOW 4.5V
HIGH 5V
LOW 4.5V
HIGH 5V
VOUT = 5V
70
VOUT = 4.5V
60
50
40
30
GND
3203 F02
IOUT(MAX) VSEL VOUT
90
EFFICIENCY (%)
ON/OFF
20
*R1
10
316k
357k
357k
402k
0
2.5
3
3.5
4
VIN (V)
4.5
5
5.5
3203 G05
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
VIN, VOUT to GND ......................................... –0.3V to 6V
MODE, VSEL/FB, SHDN ..................... –0.3V to VIN +0.3V
VOUT Short Circuit Duration ............................. Indefinite
IOUT (Note 2)....................................................... 500mA
Operating Temperature Range (Note 3) ... –40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
C2+
1
10 C1–
VOUT
2
C1+
3
SHDN
4
7 VIN
VSEL/FB*
5
6 MODE
9 GND
8 C2–
11
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C,θJA = 44°C/W,θJC = 3°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
*VSEL ON LTC3203-1/LTC3203B-1. FB ON LTC3203/LTC3203B
ORDER PART NUMBER
DD PART MARKING
LTC3203EDD
LTC3203EDD-1
LTC3203BEDD-1
LTC3203BEDD
LBQK
LCFH
LCGY
LCGX
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 specifications which apply over the full specified temperature
range, otherwise specifications are at 25°C. VIN = 3.6V, C1 = C2 = 2.2µF unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LTC3203/LTC3203-1/LTC3203B/LTC3203B-1
●
VIN
Input Voltage Range
ISHDN
Shutdown Current
SHDN = 0V, VOUT = 0V
2.7
ROL
Open Loop Output
Impedance
2x Mode (Note 4), VIN = 2.7V, VOUT = 4.5V
1.5x Mode (Note 4), VIN = 3.6V, VOUT = 4.5V
2.0
1.5
fOSC
CLK Frequency
Oscillator Free Running, 2x Mode
Oscillator Free Running, 1.5x Mode
1.0
0.9
VMODEH
MODE Input High Voltage
●
0.874
0.91
0.946
V
VMODEL
MODE Input Low Voltage
●
0.788
0.82
0.852
V
VSHDNH
SHDN Input High Voltage
●
1.3
VSHDNL
SHDN Input Low Voltage
●
0.4
V
IMODEH
MODE Input High Current
●
–1
1
µA
IMODEL
MODE Input Low Current
●
–1
1
µA
ISHDNH
SHDN Input High Current
●
–1
1
µA
ISHDNL
SHDN Input Low Current
●
–1
1
µA
●
5.5
V
1
µA
3.0
2.6
Ω
Ω
MHz
MHz
V
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full specified temperature
range, otherwise specifications are at 25°C. VIN = 3.6V, C1 = C2 = 2.2µF unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LTC3203-1/LTC3203B-1
VOUT
4.5V Output Voltage Range
(VSEL = 0V) (Note 5)
VIN > 3.1V, IOUT < 500mA
VIN > 2.9V, IOUT < 350mA
VIN > 2.7V, IOUT < 250mA
●
●
4.32
4.32
4.32
4.5
4.5
4.5
4.68
4.68
4.68
V
V
V
5V Output Voltage Range
(VSEL = VIN) (Note 5)
VIN > 3.1V, IOUT < 500mA
VIN > 3.1V, IOUT < 400mA
VIN > 2.7V, IOUT < 150mA
●
●
4.8
4.8
4.8
5
5
5
5.2
5.2
5.2
V
V
V
∆VOUT/∆IOUT
VOUT Load Regulation
VIN = 3.6V, IOUT = 100mA to 500mA, 2x Mode,
VIN = 4V, IOUT = 100mA to 500mA, 1.5x Mode
0.37
0.27
ICC
No Load Operating Current
(LTC3203-1)
IOUT = 0mA, 2x Mode
IOUT = 0mA, 1.5x Mode
120
100
No Load Operating Current
(LTC3203B-1)
IOUT = 0mA, 2x Mode
IOUT = 0mA, 1.5x Mode
9
7
VVSELH
VSEL Input High Voltage
●
VVSELL
VSEL Input Low Voltage
●
IVSELH
VSEL Input High Current
●
IVSELL
VSEL Input Low Current
●
mV/mA
mV/mA
µA
µA
300
300
mA
mA
1.3
V
0.4
V
–1
1
µA
–1
1
µA
LTC3203/LTC3203B
VFB
Feedback Servo Voltage
IOUT = 0mA, 2.7V ≤ VIN ≤ 5.5V
●
0.88
IFB
FB Input Current
VFB = 0.95V
●
–50
∆VFB/∆IOUT
Load Regulation
(Refer to FB Pin)
IOUT = 100mA to 500mA, 2x Mode, VIN = 3.6V
IOUT = 100mA to 500mA, 1.5x Mode, VIN = 4V
0.08
0.06
ICC
No Load Operating Current
(LTC3203)
IOUT = 0mA, 2x Mode, 5V VOUT Setting
IOUT = 0mA, 1.5x Mode, 5V VOUT Setting
120
100
No Load Operating Current
(LTC3203B)
IOUT = 0mA, 2x Mode, 5V VOUT Setting
IOUT = 0mA, 1.5x Mode, 5V VOUT Setting
9
7
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Based on long-term current density limitations.
Note 3: The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 are guaranteed
to meet performance specifications from 0°C to 85°C. Specifications over
the –40°C to 85°C operating temperature range are assured by design,
characterization and correlation with statistical process controls.
0.91
0.94
V
50
nA
mV/mA
mV/mA
µA
µA
300
300
mA
mA
Note 4: Output not in regulation (based on wafer sort):
ROL ≡ (2 • VIN – VOUT)/IOUT, 2x Mode
ROL ≡ (1.5 • VIN – VOUT)/IOUT, 1.5x Mode
Note 5: Proper conversion mode, 1.5x or 2x, has to be chosen based on
ROL to ensure output regulation.
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C, VIN = 3.6V, C1 = C2 = 2.2µF unless otherwise specified
VOUT vs Load Current
(4.5V Output Setting)
4.65
5.5
4.8
4.60
5.3
4.6
5.1
4.55
VIN = 3V
VIN = 2.7V
4.40
VIN = 3.3V
4.35
4.7
VIN = 3.3V
4.5
VIN = 3.6V
VIN = 2.7V
4.3
4.25
0
3.5
1.5x MODE
2x MODE
0
3.2
1.5x MODE
2x MODE
3.0
50 100 150 200 250 300 350 400 450 500
ILOAD (mA)
2.5
3.5
3
4
VIN (V)
3203 G02
3203 G01
VOUT vs Supply Voltage
(5V Output Setting)
4.5
5
5.5
3203 G03
Open-Loop Output Resistance
vs Temperature
2.5
5.4
2x MODE
VIN = 2.7V
VOUT = 4.5V
ILOAD = 0mA
5.2
2.0
5.0
ILOAD = 500mA
4.8
ROL (Ω)
VOUT (V)
3.8
3.4
3.7
50 100 150 200 250 300 350 400 450 500
ILOAD (mA)
ILOAD = 250mA
4.0
3.6
4.1
1.5x MODE
2x MODE
ILOAD = 500mA
4.2
3.9
4.30
ILOAD = 0mA
4.4
VOUT (V)
VOUT (V)
4.50
4.45
VIN = 3V
4.9
VIN = 3.6V
VOUT (V)
VOUT vs Supply Voltage
(4.5V Output Setting)
VOUT vs Load Current
(5V Output Setting)
ILOAD = 250mA
4.6
1.5
1.5x MODE
VIN = 3.6V
VOUT = 4.5V
1.0
4.4
0.5
4.2
4.0
2.5
1.5x MODE
2x MODE
3
3.5
4
VIN (V)
4.5
5
0
–40
5.5
–15
35
10
TEMPERATURE (°C)
60
3203 G06
3203 G04
Oscillator Frequency
vs Supply Voltage
Short-Circuit Current
vs Supply Voltage
1.4
1400
1.2
1200
2x MODE
1.0
1000
1.5x MODE
1.5x MODE
0.8
ISC (mA)
FREQUENCY (MHz)
85
0.6
800
600
2x MODE
0.4
400
0.2
200
0
2.5
3
3.5
4
VIN (V)
4.5
5
5.5
3203 G07
0
2.5
3
3.5
4
VIN (V)
4.5
5
5.5
3203 G08
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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TYPICAL PERFOR A CE CHARACTERISTICS
Burst Mode Current Threshold
vs Supply Voltage
(LTC3203/LTC3203-1)
No-Load Input Current vs Supply
Voltage (LTC3203/LTC3203-1)
160
500
140
450
2x MODE
1.5x MODE
10
350
80
60
300
250
200
1.5x MODE
150
40
1
1.5x MODE
IIN – 1.5 • ILOAD
0.1
100
20
2x MODE
50
0
3
3.5
4
VIN (V)
4.5
5
5.5
3
2.5
3.5
4
VIN (V)
4.5
3203 G13
IOUT
VIN = 3.6V
CIN = 2.2µF
COUT = 10µF
IOUT = 300mA
2x MODE
500mA
100mA
3203 G14
500ns/DIV
VIN = 4V
CIN = 2.2µF
COUT = 10µF
1.5x MODE
VFB Set Point vs Supply Voltage
(LTC3203/LTC3203B)
Load Transient (2x Mode)
VOUT
100mV/DIV
AC-COUPLED
0.94
0.96
0.93
0.94
TA = –40°C
TA = 25°C
0.91
0.88
TA = 85°C
VIN = 3.6V
2x MODE
0.86
0.89
0.88
VIN = 4V
1.5x MODE
0.90
0.90
3203 G16
3203 G15
0.92
VFB (V)
VFB (V)
100mA
20µs/DIV
VFB vs Load Current
(LTC3203/LTC3202B)
0.92
500mA
1000
VOUT
100mV/DIV
AC-COUPLED
VOUT
20mV/DIV
AC-COUPLED
VOUT
20mV/DIV
AC-COUPLED
20µs/DIV
100
Load Transient (1.5x Mode)
VIN
20mV/DIV
AC-COUPLED
VIN = 3.6V
CIN = 2.2µF
COUT = 10µF
2x MODE
1
10
ILOAD (mA)
3209 G12
Input and Output Ripple
(2x Mode)
VIN
20mV/DIV
AC-COUPLED
500ns/DIV
0.1
3203 G11
Input and Output Ripple
(1.5x Mode)
VIN = 4V
CIN = 2.2µF
COUT = 10µF
IOUT = 300mA
1.5x MODE
0.01
0.01
5.5
5
3203 G10
IOUT
2x MODE
IIN – 2 • ILOAD
EXTRA IIN (mA)
ILOAD (mA)
100
IIN (µA)
100
400
120
0
2.5
Extra Input Current vs Load
Current (LTC3203/LTC3203-1)
0.84
0.82
2.5
3
3.5
4
VIN (V)
4.5
5
5.5
3203 G17
0 50 100 150 200 250 300 350 400 450 500
ILOAD (mA)
3203 G18
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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PI FU CTIO S
C2+ (Pin 1): Flying Capacitor 2 Positive Terminal (C2).
VOUT (Pin 2): Regulated Output Voltage. VOUT should be
bypassed with a low ESR ceramic capacitor as close to the
pin as possible for best performance. The capacitor should
have greater than 4.7µF capacitance under all conditions.
C1+ (Pin 3): Flying Capacitor 1 Positive Terminal (C1).
SHDN (Pin 4): Active Low Shutdown Input. A low on SHDN
puts the LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 in
low current shutdown mode. Do not float the SHDN pin.
VSEL (Pin 5) (LTC3203-1/LTC3203B-1): Output Voltage
Selection Input. A logic 0 at VSEL sets the regulated VOUT
to 4.5V; and a logic 1 sets the regulated VOUT to 5V. Do not
float the VSEL pin.
FB (Pin 5) (LTC3203/LTC3203B): Feedback. The voltage
on this pin is compared to the internal reference voltage
(0.91V) by the error amplifier to keep the output in
regulation. An external resistor divider is required
between VOUT and FB to program the output voltage.
MODE (Pin 6): Mode Selection Input. The LTC3203/
LTC3203-1/LTC3203B/LTC3203B-1 operates in 1.5x
mode if the MODE pin is greater than VMODEH, which
gives higher charge pump efficiency. If the MODE pin is
less than VMODEL, the LTC3203/LTC3203-1/LTC3203B/
LTC3203B-1 operates in 2x mode, which gives a higher
charge pump boost voltage.
VIN (Pin 7): Input Supply Voltage. VIN should be bypassed
with a more than 2.2µF low ESR ceramic capacitor to GND.
C2– (Pin 8): Flying Capacitor 2 Negative Terminal (C2).
GND (Pin 9): Ground. This pin should be connected
directly to a low impedance ground plane.
C1– (Pin 10): Flying Capacitor 1 Negative Terminal (C1).
Exposed Pad (Pin 11): Ground. This pin must be soldered to the PCB for electrical contact and rated thermal
performance.
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
SW
BLOCK DIAGRA
LTC3203/LTC3203B
LTC3203-1/LTC3203B-1
0.91V
+
0.91V
+
2x/1.5x
2x/1.5x
MODE 6
VSEL
–
MODE 6
–
5
SHDN 4
SOFT-START AND
SHUTDOWN
CONTROL
SHDN 4
0.91V
SOFT-START AND
SHUTDOWN
CONTROL
5 FB
0.82V
2 VOUT
2 VOUT
+
+
OSCILLATOR
+
SWITCH CONTROL
–
0.91V
OSCILLATOR
+
SWITCH CONTROL
–
3 C1+
3 C1+
S
VIN 7
S
VIN 7
10 C1–
10 C1–
1 C2+
1 C2+
S
S
8 C2–
8 C2–
9, 11
GND
3203 F01
9, 11
GND
3203 F02
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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OPERATIO
The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 use
a switched capacitor charge pump to boost VIN to a
regulated output voltage. Regulation is achieved by sensing the output voltage through a resistor divider and
modulating the charge pump output current based on the
error signal. A two-phase non-overlapping clock activates
the charge pump switches. The typical frequency of charging and discharging the flying capacitors is 1MHz
(2x mode) or 0.9MHz (1.5x mode). A unique architecture
maintains relatively constant input current for the lowest
possible input noise.
Mode of Operation
The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 charge
pump can operate in two modes of voltage conversion:
1.5x or 2x.
In the 1.5x mode the flying capacitors are charged in series
during the first clock phase, and stacked in parallel on top
of VIN on the second clock phase. Alternatively, in the 2x
mode the flying capacitors are charged on alternate clock
phases from VIN. While one capacitor is being charged
from VIN, the other is stacked on top of VIN and connected
to the output. The two flying capacitors operate out of
phase to minimize both input and output ripple. At light
load the LTC3203/LTC3203-1 go into Burst Mode operation to reduce quiescent current.
The conversion mode should be chosen based on considerations of efficiency, available output current and VOUT
ripple. With a given VIN, the 1.5x mode gives a higher
efficiency but lower available output current. The 2x mode
gives a higher available output current but lower efficiency. Moreover, the output voltage ripple in the 2x mode
is lower due to the out-of-phase operation of the two
flying capacitors.
Generally, at low VIN, the 2x mode should be selected, and
at higher VIN, the 1.5x mode should be selected. By
connecting a resistive divider from VIN to the MODE input
pin the MODE input allows the user to accurately program
the VIN threshold at which the charge pump will switch
from 1.5x mode to 2x mode when VIN starts to fall and
vice versa. Hysteresis on the MODE pin prevents the
LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 from
switching continuously between the two modes.
Output Voltage Programming
The LTC3203-1/LTC3203B-1 has a VSEL input pin that
allows the user to program the regulated output voltage to
either 4.5V or 5V. 4.5V VOUT is useful for driving white
LEDs while a regulated VOUT of 5V is useful for powering
logic circuits.
The LTC3203/LTC3203B has a FB pin in place of the VSEL
pin that allows the output voltage to be programmed using
an external resistive divider.
Shutdown Mode
When SHDN is asserted low, the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1 enter shutdown mode. The charge
pump is first disabled, but the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1 continue to draw 5µA of supply
current. This current will drop to less than 1µA when VOUT
is fully discharged to 0V. Furthermore, VOUT is disconnected from VIN. Since the SHDN pin is a high impedance
CMOS input, it should never be allowed to float.
Burst Mode Operation
The LTC3203/LTC3203-1 provide automatic Burst Mode
operation to reduce quiescent current of the power converter at light loads. Burst Mode operation is initiated if the
output load current falls below an internally programmed
threshold. Once Burst Mode operation is initiated, the part
shuts down the internal oscillator to reduce the switching
losses and goes into a low current state. This state is
referred to as the Sleep state in which the chip consumes
only about 120µA from the input.
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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OPERATIO
When the output voltage drops enough to overcome the
burst comparator hysteresis, the part wakes up and commences normal fixed frequency operation. The output
capacitor recharges and causes the part to re-enter the
Sleep state if the output load still remains less than the
Burst Mode threshold. This Burst Mode threshold varies
with VIN, VOUT and the choice of output storage capacitor.
Short-Circuit/Thermal Protection
The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 have
built-in short-circuit current limit as well as over-temperature protection. During a short-circuit condition, the chip
will automatically limit the output current to approximately
1A. At higher temperatures, or if the input voltage is high
enough to cause excessive self-heating of the part, the
thermal shutdown circuitry will shut down the charge
pump once the junction temperature exceeds approximately 150°C. It will enable the charge pump once the
junction temperature drops back to approximately 135°C.
The LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 will
cycle in and out of thermal shutdown indefinitely without
latch-up or damage until the short circuit condition on
VOUT is removed.
Soft-Start
To prevent excessive current flow at VIN during start-up,
the LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 have
built-in soft-start circuitry. Soft-start is achieved by increasing the amount of current available to the output
charge storage capacitor linearly over a period of approximately 250µs.
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LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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APPLICATIO S I FOR ATIO
Power Efficiency
The power efficiency (η) of the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1 in 1.5x mode is similar to that of
a linear regulator with an effective input voltage of 1.5
times the actual input voltage. This occurs because the
input current for a 1.5x fractional charge pump is approximately 1.5 times the load current. In an ideal regulating
1.5x charge pump the power efficiency would be given by:
η1.5 XIdeal =
POUT
V
•I
V
= OUT OUT = OUT
PIN
VIN • 1.5IOUT 1.5 VIN
Similarly, in 2x mode, the efficiency is similar to that of a
linear regulator with an effective input voltage of twice the
actual input voltage. In an ideal regulating voltage doubler
the power efficiency would be given by:
η2 XIdeal =
POUT VOUT • IOUT VOUT
=
=
PIN
VIN • 2IOUT
2 VIN
At moderate to high output power the switching losses
and quiescent current of the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1 are negligible and the expression
above is valid.
As evident from the above two equations, with the same
VIN, the 1.5x mode will give higher efficiency than the
2x mode.
Programming the LTC3203/LTC3203B Output Voltage
(FB Pin)
While the LTC3203-1/LTC3203B-1 have internal resistive
dividers to program the output voltage, the programmable
LTC3203/LTC3203B may be set to an arbitrary voltage via
an external resistive divider. Since it operates as a voltage
doubling charge pump when MODE is less than VMODEL,
it is not possible to achieve output voltages greater than
twice the available input voltage in this case. Similarly,
when MODE is greater than VMODEH, the achievable output
voltage is less than 1.5 times the available input voltage.
Figure 1 shows the required voltage divider connection.
2
VOUT
LTC3203/
LTC3203B
5
FB
CFB
R1
COUT
R2
GND
9, 11
3203 F01
Figure 1. Programming the LTC3203/LTC3203B Output Voltage
The voltage divider ratio is given by the expression:
R1 VOUT
⎛ R1 ⎞
=
− 1 or VOUT = ⎜ + 1⎟ • 0.91V
⎝ R2 ⎠
R2 0.91V
Typical values for total voltage divider resistance can
range from several kΩs up to 1MΩ. The compensation
capacitor (CFB) is necessary to counteract the pole caused
by the large valued resistors R1 and R2, and the input
capacitance of the FB pin. For best results, CFB should be
5pF for all R1 or R2 greater than 10k and can be omitted
if both R1 and R2 are less than 10k.
The LTC3203/LTC3203B can also be configured to control
a current. In white LED applications the LED current is
programmed by the ratio of the feedback set point voltage
and a sense resistor as shown in Figure 2. The current of
the remaining LEDs is controlled by virtue of their similarity to the reference LED and the ballast voltage across the
sense resistor.
2
ILED =
VFB
RX
VOUT
LTC3203/
LTC3203B
FB
GND
9, 11
5
•••
COUT
RX
RX
3203 F02
Figure 2. Programming the LTC3203/LTC3203B Output Current
In this configuration the feedback factor (∆VOUT/∆IOUT)
will be very near unity since the small signal LED impedance will be considerably less than the current setting
32031fa
10
LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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APPLICATIO S I FOR ATIO
resistor RX. Thus, this configuration will have the highest
loop gain giving it the lowest closed-loop output resistance. Likewise it will also require the largest amount of
output capacitance to preserve stability.
Programming the MODE Pin
Effective Open Loop Output Resistance (ROL)
When VIN ramps up, the voltage at the MODE pin crosses
VMODEH and the chip switches from 2x mode to 1.5x mode.
When VIN starts to drop, the voltage at the MODE pin
crosses VMODEL and the chip switches back to 2x mode.
The MODE pin resistor ratio must be selected such that at
the switch point the output is still able to maintain regulation at maximum IOUT:
The effective open loop output resistance (ROL) of a
charge pump is a very important parameter, which determines its strength. The value of this parameter depends on
many factors such as the oscillator frequency (fOSC), the
value of the flying capacitor (CFLY), the non-overlap time,
the internal switch resistances (RS), and the ESR of the
external capacitors.
Figure 3 shows how the LTC3203/LTC3203-1/LTC3203B/
LTC3203B-1 can be modeled as a Thevenin-equivalent
circuit.
Thus the maximum available output current and voltage
can be calculated from the effective open-loop output
resistance, ROL, and the effective output voltage, 1.5VIN
(in 1.5x mode) or 2VIN (in 2x mode). From Figure 3, the
available current is given by:
IOUT =
1.5 • VIN(1.5x) – VOUT > IOUT • ROL(1.5X)
The minimum VIN operating in 1.5x mode occurs at the
switch point where:
Maximum Available Output Current
IOUT =
By connecting a resistor divider to the MODE pin, the VIN
voltage at which the chip switches modes can be accurately programmed.
1.5VIN − VOUT
In 1.5x mod e
ROL
⎛R
⎞
VIN = VMODEL • ⎜ MODE1 + 1⎟
⎝ RMODE2 ⎠
therefore:
⎛R
⎞
1.5 • VMODEL • ⎜ MODE1 + 1⎟
⎝ RMODE2 ⎠
> ROL(1.5X )(MAX ) • IOUT(MAX ) + VOUT(MIN)
RMODE1 VOUT(MIN) + ROL(1.5x )(MAX ) • IOUT(MAX )
–1
>
1.5 • VMODEL
RMODE2
2VIN − VOUT
In 2x mod e
ROL
As evident from the above two equations, with the same
VIN and ROL, the 2x mode will give more output current
than the 1.5x mode.
7
VIN
LTC3203/
LTC3203B 6
MODE
RMODE1
CIN
RMODE2
ROL
1.5VIN
OR
2VIN
+
–
+
VOUT
GND
9, 11
3203 F04
Figure 4
–
3203 F03
Figure 3. Charge Pump Open-Loop Thevenin-Equivalent Circuit
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11
LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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APPLICATIO S I FOR ATIO
For the example given, a 5V output setting with ±4% output
tolerance and maximum load current of 500mA, a resistor
ratio of:
RMODE1
>4
RMODE2
at the MODE pin allows the chip to switch modes while
maintaining regulation.
VIN, VOUT Capacitor Selection
The style and value of capacitors used with the
LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 determine
several important parameters such as regulator control
loop stability, output ripple, charge pump strength and
minimum start-up time.
To reduce noise and ripple, it is recommended that low
equivalent series resistance (ESR) multilayer ceramic chip
capacitors (MLCCs) be used for both CIN and COUT. Tantalum and aluminum capacitors are not recommended because of their high ESR.
In 1.5x mode, the value of COUT directly controls the
amount of output ripple for a given load current. Increasing
the size of COUT will reduce the output ripple at the expense
of higher minimum turn-on time and higher start-up current. The peak-to-peak output ripple for 1.5x mode is given
by the expression:
VRIPPLE(P − P) =
IOUT
3 fOSC • COUT
where f OSC is the LTC3203/LTC3203-1/LTC3203B/
LTC3203B-1’s oscillator frequency (typically 0.9MHz) and
COUT is the output charge storage capacitor.
In 2x mode, the output ripple is very low due to the out-ofphase operation of the two flying capacitors. VOUT remains
almost flat when either of the flying capacitors is connected
to VOUT.
Both the type and value of the output capacitor can significantly affect the stability of the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1. As shown in the Block Diagram,
the LTC3203/LTC3203-1/LTC3203B/LTC3203B-1 use a
control loop to adjust the strength of the charge pump to
match the current required at the output. The error signal
of this loop is stored directly on the output charge storage
capacitor. The charge storage capacitor also serves to
form the dominant pole for the control loop. To prevent
ringing or instability, it is important for the output capacitor to maintain at least 4.7µF of capacitance over all
conditions. Note that the actual capacitance of ceramic
capacitors usually drops when biased with DC voltage.
Different capacitor types drop to different extents. Make
sure that the selected ceramic capacitors have enough
capacitance when biased with the required DC voltage.
Likewise, excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1. The closed-loop output resistance of the LTC3203/LTC3203-1/LTC3203B/LTC3203B1 are designed to be 0.27Ω (at 1.5x mode). For a 100mA
load current change, the output voltage will change by
about 27mV. If the output capacitor has 0.27Ω or more of
ESR, the closed-loop frequency response will cease to
roll-off in a simple one-pole fashion and poor load transient response or instability could result. Multilayer ceramic chip capacitors typically have exceptional ESR performance and, combined with a good board layout, should
yield very good stability and load transient performance.
As the value of COUT controls the amount of output ripple,
the value of CIN controls the amount of ripple present at the
input pin (VIN). The input current to the LTC3203/
LTC3203-1/LTC3203B/LTC3203B-1 will be relatively constant while the charge pump is on either the input charging
phase or the output charging phase but will drop to zero
during the clock non-overlap times. Since the non-overlap
time is small (~40ns) these missing “notches” will result
in only a small perturbation on the input power supply line.
Note that a higher ESR capacitor such as tantalum
will have higher input noise by the amount of the input
current change times the ESR. Therefore ceramic
capacitors are again recommended for their exceptional
ESR performance. Further input noise reduction can be
achieved by powering the LTC3203/LTC3203-1/LTC3203B/
LTC3203B-1 through a very small series inductor as
shown in Figure 5.
32031fa
12
LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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APPLICATIO S I FOR ATIO
10nH
VIN
0.1µF
7
VIN
2.2µF LTC3203*
9, 11
GND
3203 F05
Figure 5. 10nH Inductor Used for Input Noise Reduction
A 10nH inductor will reject the fast current notches,
thereby presenting a nearly constant current load to the
input power supply. For economy the 10nH inductor can
be fabricated on the PC board with about 1cm (0.4") of PC
board trace.
Flying Capacitor Selection
Warning: Polarized capacitors such as tantalum or
aluminum should never be used for the flying capacitors
since their voltage can reverse upon start-up of the
LTC3203/LTC3203-1/LTC3203B/LTC3203B-1. Low ESR
ceramic capacitors should always be used for the flying
capacitors.
The flying capacitors control the strength of the charge
pump. In order to achieve the rated output current, it is
necessary to have at least 2.2µF of capacitance for each of
the flying capacitors.
Ceramic capacitors of different materials lose their capacitance with higher temperature and voltage at different
rates. For example, a capacitor made of X7R material will
retain most of its capacitance from –40°C to 85°C whereas
Z5U or Y5V style capacitors will lose considerable capacitance over that range. Z5U and Y5V capacitors may also
have a poor voltage coefficient causing them to lose 60%
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
comparing the specified capacitance value. For example,
over rated voltage and temperature conditions, a 4.7µF,
10V, Y5V ceramic capacitor in a 0805 case may not
provide any more capacitance than a 1µF, 10V, X5R or
X7R capacitor available in the same 0805 case. In fact,
over bias and temperature range the 1µF, 10V, X5R or X7R
will provide more capacitance than the 4.7µF, 10V, Y5V
capacitor. The capacitor manufacturer’s data sheet should
be consulted to determine what value of capacitor is
needed to ensure minimum capacitance values are met
over operating temperature and bias voltage.
Below is a list of ceramic capacitor manufacturers and
how to contact them:
AVX
www.avxcorp.com
Kemet
www.kemet.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay
www.vishay.com
TDK
www.component.tdk.com
32031fa
13
LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
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APPLICATIO S I FOR ATIO
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3203/
LTC3203-1/LTC3203B/LTC3203B-1. If the junction temperature increases above approximately 150°C, the thermal shutdown circuitry will automatically deactivate the
output. To reduce the maximum junction temperature, a
good thermal connection to the PC board is recommended.
Connecting GND (Pin 9) and the exposed pad (Pin 11) of
the DFN package to a ground plane under the device on two
layers of the PC board can reduce the thermal resistance
of the package and PC board considerably.
if the flying capacitors are not close to the part (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 LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1 pins. For a high quality AC ground
it should be returned to a solid ground plane that extends
all the way to the LTC3203/LTC3203-1/LTC3203B/
LTC3203B-1. To prevent degraded performance, the FB
trace should be kept away or be shielded from the flying
capacitor traces.
GROUND PLANE
C1
Layout Considerations
Due to the high switching frequency and high transient
currents produced by the LTC3203/LTC3203-1/
LTC3203B/LTC3203B-1, careful board layout is necessary for optimum performance. A true ground plane and
short connections to all the external capacitors will
improve performance and ensure proper regulation
under all conditions.
The flying capacitor pins C1+, C2+, C1– and C2– 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
COUT
C2
1
10
2
3
9
11
8
4
7
5
6
CIN
3206 F07
LTC3203/LTC3203B COMPONENTS NOT USED
IN LTC3203-1 OR LTC3203B-1
Figure 6. Recommended Layouts
32031fa
14
LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD) DFN 1103
5
0.25 ± 0.05
0.200 REF
0.50
BSC
2.38 ±0.05
(2 SIDES)
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
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
32031fa
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.
15
LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
U
TYPICAL APPLICATIO
7
3
2.2µF
10
332k
100k
1
C2+
C2–
4
2
C1+ LTC3203/
LTC3203B
C1–
8
6
VOUT
VIN
FB
10µF
5
MODE
SHDN
GND
ON OFF
47Ω
47Ω
47Ω
47Ω
47Ω
47Ω
9, 11
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32031fa
16
Linear Technology Corporation
LT/LWI 1006 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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