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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1 500mA Output Current Low Noise Dual Mode Step-Up Charge Pumps DESCRIPTIO
The LTC(R)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. 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 x 3mm) 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. *Protected by U.S. Patents including 6411531.
FEATURES

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(R) Operation with IQ ~ 120A (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: < 1A Available in a 10-pin (3mm x 3mm) DFN Package
APPLICATIO S

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
TYPICAL APPLICATIO
ON/OFF
Efficiency vs VIN at 300mA Load Current
100 OUTPUT PROGRAMMING 90 80 VOUT 500mA 10F 2.2F EFFICIENCY (%) 70 60 50 40 30
3203 F02
SHDN VSEL LTC3203-1 VIN 2.2F 2.2F R1* VIN C1+ C1- MODE 100k IOUT(MAX) VSEL VOUT 300mA 300mA 500mA 500mA LOW 4.5V HIGH 5V LOW 4.5V HIGH 5V VOUT C2+ C2- GND *R1 316k 357k 357k 402k
20 10 0 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
3203 G05
U
U
U
VOUT = 5V VOUT = 4.5V
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW C2+ VOUT C1+ SHDN VSEL/FB* 1 2 3 4 5
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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) ... -40C to 85C Storage Temperature Range .................. -65C to 125C
10 C1- 9 GND 8 C2- 7 VIN 6 MODE
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 125C,JA = 44C/W,JC = 3C/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 LTC3203EDD LTC3203EDD-1 LTC3203BEDD-1 LTC3203BEDD
DD PART MARKING 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.
The denotes specifications which apply over the full specified temperature range, otherwise specifications are at 25C. VIN = 3.6V, C1 = C2 = 2.2F unless otherwise specified.
SYMBOL VIN ISHDN ROL fOSC VMODEH VMODEL VSHDNH VSHDNL IMODEH IMODEL ISHDNH ISHDNL PARAMETER Input Voltage Range Shutdown Current Open Loop Output Impedance CLK Frequency MODE Input High Voltage MODE Input Low Voltage SHDN Input High Voltage SHDN Input Low Voltage MODE Input High Current MODE Input Low Current SHDN Input High Current SHDN Input Low Current SHDN = 0V, VOUT = 0V 2x Mode (Note 4), VIN = 2.7V, VOUT = 4.5V 1.5x Mode (Note 4), VIN = 3.6V, VOUT = 4.5V Oscillator Free Running, 2x Mode Oscillator Free Running, 1.5x Mode

ELECTRICAL CHARACTERISTICS
LTC3203/LTC3203-1/LTC3203B/LTC3203B-1
CONDITIONS

MIN 2.7
TYP
MAX 5.5 1
UNITS V A MHz MHz
2.0 1.5 1.0 0.9 0.874 0.788 1.3 0.91 0.82
3.0 2.6
0.946 0.852 0.4
-1 -1 -1 -1
1 1 1 1
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V V V V A A A A
W
U
U
WW
W
LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
The denotes specifications which apply over the full specified temperature range, otherwise specifications are at 25C. VIN = 3.6V, C1 = C2 = 2.2F unless otherwise specified.
SYMBOL VOUT PARAMETER 4.5V Output Voltage Range (VSEL = 0V) (Note 5) 5V Output Voltage Range (VSEL = VIN) (Note 5) VOUT/IOUT ICC VOUT Load Regulation No Load Operating Current (LTC3203-1) No Load Operating Current (LTC3203B-1) VVSELH VVSELL IVSELH IVSELL LTC3203/LTC3203B VFB IFB VFB/IOUT ICC Feedback Servo Voltage FB Input Current Load Regulation (Refer to FB Pin) No Load Operating Current (LTC3203) No Load Operating Current (LTC3203B) IOUT = 0mA, 2.7V VIN 5.5V VFB = 0.95V IOUT = 100mA to 500mA, 2x Mode, VIN = 3.6V IOUT = 100mA to 500mA, 1.5x Mode, VIN = 4V IOUT = 0mA, 2x Mode, 5V VOUT Setting IOUT = 0mA, 1.5x Mode, 5V VOUT Setting IOUT = 0mA, 2x Mode, 5V VOUT Setting IOUT = 0mA, 1.5x Mode, 5V VOUT Setting

ELECTRICAL CHARACTERISTICS
CONDITIONS VIN > 3.1V, IOUT < 500mA VIN > 2.9V, IOUT < 350mA VIN > 2.7V, IOUT < 250mA VIN > 3.1V, IOUT < 500mA VIN > 3.1V, IOUT < 400mA VIN > 2.7V, IOUT < 150mA VIN = 3.6V, IOUT = 100mA to 500mA, 2x Mode, VIN = 4V, IOUT = 100mA to 500mA, 1.5x Mode IOUT = 0mA, 2x Mode IOUT = 0mA, 1.5x Mode IOUT = 0mA, 2x Mode IOUT = 0mA, 1.5x Mode

MIN 4.32 4.32 4.32 4.8 4.8 4.8
TYP 4.5 4.5 4.5 5 5 5 0.37 0.27 120 100 9 7
MAX 4.68 4.68 4.68 5.2 5.2 5.2
UNITS V V V V V V mV/mA mV/mA
LTC3203-1/LTC3203B-1

300 300
A A mA mA V
VSEL Input High Voltage VSEL Input Low Voltage VSEL Input High Current VSEL Input Low Current
1.3 0.4 -1 -1 0.88 -50 0.08 0.06 120 100 9 7 300 300 0.91 1 1 0.94 50
V A A V nA mV/mA mV/mA A A mA mA
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 0C to 85C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
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 TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25C, VIN = 3.6V, C1 = C2 = 2.2F unless otherwise specified VOUT vs Load Current (4.5V Output Setting)
4.65 4.60 4.55 VIN = 3.6V VOUT (V) VOUT (V) 4.50 4.45 4.40 4.35 4.30 4.25 0 1.5x MODE 2x MODE 50 100 150 200 250 300 350 400 450 500 ILOAD (mA)
3203 G01
VIN = 3V VIN = 2.7V VIN = 3.3V
4.5 4.3 4.1 3.9 3.7 3.5 0
VIN = 3.3V VIN = 3.6V VIN = 2.7V
VOUT (V)
VOUT vs Supply Voltage (5V Output Setting)
5.4 5.2 5.0 ILOAD = 500mA ILOAD = 0mA
2.0 2.5
VOUT (V)
ILOAD = 250mA 4.6 4.4
ROL ()
4.8
4.2 4.0 2.5
3
Oscillator Frequency vs Supply Voltage
1.4 1.2 2x MODE
FREQUENCY (MHz)
1.0 1.5x MODE 0.8 0.6 0.4 0.2 0 2.5
ISC (mA)
3
4
UW
3.5
VOUT vs Load Current (5V Output Setting)
5.5 5.3 5.1 4.9 4.7 VIN = 3V
4.8 4.6 4.4 4.2
VOUT vs Supply Voltage (4.5V Output Setting)
ILOAD = 0mA
ILOAD = 500mA ILOAD = 250mA
4.0 3.8 3.6 3.4
1.5x MODE 2x MODE 50 100 150 200 250 300 350 400 450 500 ILOAD (mA)
3203 G02
3.2 3.0 2.5 3 3.5 4 VIN (V) 4.5
1.5x MODE 2x MODE 5 5.5
3203 G03
Open-Loop Output Resistance vs Temperature
2x MODE VIN = 2.7V VOUT = 4.5V
1.5 1.5x MODE VIN = 3.6V VOUT = 4.5V
1.0
0.5
1.5x MODE 2x MODE 4 VIN (V) 4.5 5 5.5
3203 G04
0 -40
-15
35 10 TEMPERATURE (C)
60
85
3203 G06
Short-Circuit Current vs Supply Voltage
1400 1200 1000 1.5x MODE 800 600 2x MODE 400 200 0 2.5
3.5
4 VIN (V)
4.5
5
5.5
3203 G07
3
3.5
4 VIN (V)
4.5
5
5.5
3203 G08
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1 TYPICAL PERFOR A CE CHARACTERISTICS
No-Load Input Current vs Supply Voltage (LTC3203/LTC3203-1)
160 140 120 100 2x MODE 1.5x MODE
ILOAD (mA)
IIN (A)
300 250 200 150 1.5x MODE
80 60 40 20 0 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
3203 G10
EXTRA IIN (mA)
Input and Output Ripple (1.5x Mode)
VIN 20mV/DIV AC-COUPLED
VIN 20mV/DIV AC-COUPLED
VOUT 20mV/DIV AC-COUPLED
VIN = 4V CIN = 2.2F COUT = 10F IOUT = 300mA 1.5x MODE
500ns/DIV
Load Transient (2x Mode)
0.94
VOUT 100mV/DIV AC-COUPLED
VFB (V)
IOUT
500mA 100mA
0.91 TA = 85C 0.90
VFB (V)
VIN = 3.6V CIN = 2.2F COUT = 10F 2x MODE
20s/DIV
UW
Burst Mode Current Threshold vs Supply Voltage (LTC3203/LTC3203-1)
500 450 400 350
10 100
Extra Input Current vs Load Current (LTC3203/LTC3203-1)
2x MODE IIN - 2 * ILOAD 1 1.5x MODE IIN - 1.5 * ILOAD 0.1
100 50 0 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
3203 G11
2x MODE
0.01 0.01 0.1 1 10 ILOAD (mA) 100 1000
3209 G12
Input and Output Ripple (2x Mode)
VOUT 100mV/DIV AC-COUPLED
Load Transient (1.5x Mode)
VOUT 20mV/DIV AC-COUPLED
IOUT
500mA 100mA
3203 G13
VIN = 3.6V CIN = 2.2F COUT = 10F IOUT = 300mA 2x MODE
500ns/DIV
3203 G14
VIN = 4V CIN = 2.2F COUT = 10F 1.5x MODE
20s/DIV
3203 G15
VFB Set Point vs Supply Voltage (LTC3203/LTC3203B)
0.96 0.94 0.92 TA = -40C TA = 25C 0.90 0.88
VFB vs Load Current (LTC3203/LTC3202B)
0.93 0.92
VIN = 4V 1.5x MODE VIN = 3.6V 2x MODE
0.86 0.84 0.82 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
3203 G17
3203 G16
0.89 0.88
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
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 4.7F 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 2.2F 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.
6
U
U
U
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
BLOCK DIAGRA
LTC3203-1/LTC3203B-1
0.91V
+
2x/1.5x
MODE 6 VSEL 5
-
SHDN 4
SOFT-START AND SHUTDOWN CONTROL
+ -
VIN 7
SW
LTC3203/LTC3203B
0.91V
+
2x/1.5x
MODE 6
-
0.91V 0.82V 2 VOUT OSCILLATOR + SWITCH CONTROL
SHDN 4
SOFT-START AND SHUTDOWN CONTROL
5 FB 2 VOUT
+ -
0.91V
OSCILLATOR + SWITCH CONTROL
3 C1+
S
3 C1+ VIN 7
S
10 C1-
10 C1-
1 C2+
S
1 C2+
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 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
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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 5A of supply current. This current will drop to less than 1A 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 120A from the input.
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1 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
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thermal shutdown circuitry will shut down the charge pump once the junction temperature exceeds approximately 150C. It will enable the charge pump once the junction temperature drops back to approximately 135C. 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 250s.
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
APPLICATIO S I FOR ATIO
Power Efficiency The power efficiency () 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:
1.5 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:
2 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.
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2 VOUT LTC3203/ LTC3203B 5 FB GND 9, 11 CFB R1 COUT R2
3203 F01
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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 ks up to 1M. 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.
ILED = VFB RX
2 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
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
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. Effective Open Loop Output Resistance (ROL) 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. Maximum Available Output Current 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 = 1.5VIN - VOUT In 1.5x mod e ROL 2VIN - VOUT In 2x mod e ROL
IOUT =
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.
ROL 1.5VIN OR 2VIN
+
VOUT
+ -
-
3203 F03
Figure 3. Charge Pump Open-Loop Thevenin-Equivalent Circuit
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Programming the MODE Pin By connecting a resistor divider to the MODE pin, the VIN voltage at which the chip switches modes can be accurately programmed. 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: 1.5 * VIN(1.5x) - VOUT > IOUT * ROL(1.5X) The minimum VIN operating in 1.5x mode occurs at the switch point where: 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
7 VIN LTC3203/ LTC3203B 6 MODE GND 9, 11
3203 F04
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RMODE1 CIN RMODE2
Figure 4
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
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,
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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 4.7F 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 0.27 (at 1.5x mode). For a 100mA load current change, the output voltage will change by about 27mV. If the output capacitor has 0.27 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
W
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
APPLICATIO S I FOR ATIO
VIN
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 2.2F 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 -40C to 85C 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%
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10nH
W
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7
VIN
0.1F
2.2F LTC3203*
9, 11
GND
3203 F05
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 4.7F, 10V, Y5V ceramic capacitor in a 0805 case may not provide any more capacitance than a 1F, 10V, X5R or X7R capacitor available in the same 0805 case. In fact, over bias and temperature range the 1F, 10V, X5R or X7R will provide more capacitance than the 4.7F, 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 Kemet Murata Taiyo Yuden Vishay TDK www.avxcorp.com www.kemet.com www.murata.com www.t-yuden.com www.vishay.com www.component.tdk.com
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
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 150C, 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. 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
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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
W
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U
COUT
C2
1
2
3
4
5
11
10
9
8
7
6
CIN
3206 F07
LTC3203/LTC3203B COMPONENTS NOT USED IN LTC3203-1 OR LTC3203B-1
Figure 6. Recommended Layouts
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
PACKAGE DESCRIPTIO U
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10 3.00 0.10 (4 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) 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 PIN 1 TOP MARK (SEE NOTE 6) 5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES) BOTTOM VIEW--EXPOSED PAD 1 1.65 0.10 (2 SIDES)
(DD) DFN 1103
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES)
0.25 0.05 0.50 BSC
0.00 - 0.05
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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.
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LTC3203/LTC3203-1 LTC3203B/LTC3203B-1
TYPICAL APPLICATIO
2.2F 332k
100k ON OFF
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ThinSOT is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
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7 3 10 1 8 6 4 VIN VOUT 2 10F 5 C1+ LTC3203/ LTC3203B C1- C2+ C2- MODE SHDN GND 9, 11 47 47 47 47 47 47 FB
32031fa LT/LWI 1006 REV A * PRINTED IN USA
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(c) LINEAR TECHNOLOGY CORPORATION 2006

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