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LTC3230 5-LED Main/Sub Display Driver with Dual LDO FEATURES

DESCRIPTION
The LTC(R)3230 is a low noise charge pump DC/DC converter designed to drive 4 Main LEDs and 1 Sub LED, plus two 200mA linear regulators to provide additional system power. The LTC3230 charge pump requires only four small ceramic capacitors and one current set resistor to form a complete LED power supply and current controller. Built-in soft-start circuitry prevents excessive inrush current during start-up and mode changes. High switching frequency enables the use of small external capacitors. Main and Sub full-scale current settings are programmed by a single external resistor. Charge pump efficiency is optimized based on the voltage across the LED current sources. The part powers up in 1x mode and automatically switches to the next higher mode, 1.5x and subsequently 2x, whenever any LED current source approaches dropout. Two 200mA linear regulators have independent enable and output voltage select pins. Each regulator can be set to one of three pre-selected output voltages with tri-level input pins. The regulators may be enabled independently of the charge pump. The LTC3230 is available in a low profile (0.75mm) 3mm x 3mm 20-lead QFN package.
Low Noise Charge Pump Provides High Efficiency with Automatic Mode Switching Multimode Operation: 1x, 1.5x, 2x Full-Scale Current Set Resistor Up to 125mA Total LED Current Single Wire Enable/Brightness Control for Main and Sub Display LEDs 32:1 Linear LED Brightness Control Dual 200mA Linear Regulators Four 25mA Low Dropout Main LED Current Sources One 25mA Low Dropout Sub LED Current Source Low Noise Constant Frequency Operation Low Shutdown Current: 3A Internal Soft-Start Limits Inrush Current During Start-Up and Mode Switching Open/Short LED Protection No Inductors 20-Lead 3mm x 3mm QFN Package
APPLICATIONS
Multi-LED Driver and Dual LDO Supplies for Cell Phone, PDA, Digital Camera and PND Applications
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6411531.
TYPICAL APPLICATION
C1 1mF C2 1mF
Efficiency vs VIN Voltage
100 90
MAIN C6 1mF D1 D2 D3 D4 SUB
C3 2.2mF ENM ENS
EFFICIENCY (PLED/PIN) (%)
VIN = 2.7V TO 5.5V
C1P C1M C2P C2M 125mA CPO VIN LTC3230 ENM ENS ENLDO1 ENLDO2 V1 V2 RSET MLED1 MLED2 MLED3 MLED4 SLED LDO1 LDO2
80 70 60 50 40 30 20 10 0 3 3.2 3.4 3.6 3.8 VIN (V) 4 4.2 4.4 4 LEDs AT 9mA/LED VF = 3V TA = 25C
D5
C4 1mF C5 1mF
1.5V 200mA 2.8V 200mA
3230 TA01a
RSET 17.4k 1% ENM OR ENS
GND
SET BRIGHTNESS LEVEL
ON
OFF
3230 TA01b
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LTC3230 ABSOLUTE MAXIMUM RATINGS
(Notes 1-5)
PIN CONFIGURATION
TOP VIEW C1M MLED3 C2M 15 LDO1 14 LDO2 21 13 V1 12 V2 11 ENM 6 SLED 7 MLED1 8 MLED2 9 10 MLED4 C1P CPO 1 ENLDO1 2 ENLDO2 3 RSET 4 ENS 5 C2P VIN 20 19 18 17 16
VIN, CPO....................................................... -0.3V to 6V ENM, ENS, ENLDO1, ENLDO2, V1, V2, LDO1, LDO2 ......................-0.3V to (VIN + 0.3V) ICPO (Note 2) ........................................................200mA LD01, LD02 (Note 3)............................................200mA MLED1-4, SLED, RSET.................................. -0.3V to 6V Operating Ambient Temperature Range (Note 4).................................................... -40C to 85C Junction Temperature ........................................... 125C Storage Temperature Range................... -65C to 150C
UD PACKAGE 20-LEAD (3mm x 3mm) PLASTIC QFN TJMAX = 125C, JA = 68C/W EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3230EUD#PBF TAPE AND REEL LTC3230EUD#TRPBF PART MARKING LCYB PACKAGE DESCRIPTION 20-Lead (3mm x 3mm) Plastic QFN TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER VIN Operating Voltage IVIN Operating Current CONDITIONS
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V, C1 = C2 = C4 = C5 = C6 = 1F, RSET = 17.4k, ENM = ENS = high, ENLDO1 = ENLDO2 = low, unless otherwise noted.
MIN
TYP 0.48 1.2 1.6
MAX 5.5
UNITS V mA mA mA
2.7
ICPO = 0, 1x Mode ICPO = 0, 1.5x Mode ICPO = 0, 2x Mode ENM = ENS = ENLD02 = ENLD01 = Low
VIN Shutdown Current LED Current Ratio (ILED/IRSET) LED Dropout Voltage LED Current Matching MLED/SLED Current, 5-Bit Linear DAC Unused LED Detection Threshold Voltage Test Current
3 555
9
A A/A mV % mA mA
MLED1, MLED2, MLED3, MLED4 and SLED Currents Mode Switch Threshold, IMLED = 15mA Any Two MLED Outputs, IMLED = Full Scale 1 ENM/ENS Strobe (FS) 31 ENM/ENS Strobes (FS/31) VCPO - MLED LED Tied to CPO

100 0.5 25.5 0.860 200 39 780 178
mV A
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LTC3230 ELECTRICAL CHARACTERISTICS
PARAMETER CPO Short Circuit Detection Threshold Voltage Charge Pump (CPO) 1x Mode Output Voltage 1.5x Mode Output Voltage 2x Mode Output Voltage 1x Mode Output Impedance 1.5x Mode Output Impedance 2x Mode Output Impedance Clock Frequency Mode Switching Delay tEN LDO1, LDO2 Bias per 1 LDO Additional DC Bias per LDO Output Voltage Accuracy Current Limit Line Regulation Load Regulation Dropout Voltage V1, V2 VIL VIH Shutdown Input Current Active Input Current ENM, ENS, ENLDO1, ENLDO2 VIL VIH IIH IIL ENM, ENS Timing tPWH tPWL tSD RSET VRSET IRSET

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V, C1 = C2 = C4 = C5 = C6 = 1F, RSET = 17.4k, ENM = ENS = high, ENLDO1 = ENLDO2 = low, unless otherwise noted.
CONDITIONS MIN 0.4 VIN 4.5 5.0 1.6 VIN = 3.4V, VCPO = 4.6V (Note 6) VIN = 3.4V, VCPO = 5.1V (Note 6) 7.9 9.2 0.9 0.5 Current Source Enable Time (ENM, ENS = High) (Note 7) ENM = ENS = Low IOUT = 100A VLDO = 1.8V, IOUT = 50mA VIN = 3.6V, 100A < ILDO < 200mA LDO2, VLDO = 3.3V, VIN - VLDO at VLDO 3% Down from VLDO Measureed at VIN = 4.3V

TYP
MAX 1.3
UNITS V V V V MHz ms
ICPO = 0mA ICPO = 0mA ICPO = 0mA
250
s
125 60 -3 280 475 0.1 0.65 250 3 750
A A % mA %/V % mV
0.2 VIN - 0.2 -1 -3 1 3 0.4 1.4 3 -1 0.2 0.2 20 250 768 800 832 70 1
V V A A V V A A s s s mV A
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ENLDO1 = ENLDO2 = Low ENLDO1 = ENLDO2 = High
VIH = 3.6V VIL = 0V High Pulse Width Low Pulse Width Low Time to Shutdown (ENM, ENS = Low)

3
LTC3230 ELECTRICAL CHARACTERISTICS
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. Assumes an operating duty cycle of 10% under absolute maximum conditions for durations less than 10 seconds. Maximum current for continuous operation is 125mA. Note 3: Based on long-term current density limitations. LD01 and LD02 have short circuit protection which limits current to no more than 750mA. Assumes an operating short circuit duty cycle less than 3% for durations less than 10 seconds. Note 4: The LTC3230 is guaranteed to meet performance specifications from 0C to 85C. Specifications over the -40C to 85C ambient operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 6: 1.5x mode output impedance is defined as (1.5VIN - VCPO)/IOUT. 2x mode output impedance is defined as (2VIN - VCPO)/IOUT. Note 7: If the part has been shut down then the initial enable time is about 100s longer due to the bandgap start-up and charge pump soft-start times.
TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Time from Enable
1.5x CPO 2V/DIV 1x 2x CPO 2V/DIV 1x
TA = 25C unless otherwise noted. 1.5x CPO Ripple
Dropout Time when Enabled
1.5x 2x
MODE RESET ENM 2V/DIV ENM 2V/DIV
VCPO 20mV/DIV AC COUPLED
ENS = LOW
400s/DIV
3230 G01
ENS = HIGH
400s/DIV
3230 G02
VIN = 3V 400ns/DIV ICPO = 80mA C1 = C2 = C6 = 1F
3230 G03
2x CPO Ripple
2.0
1x Mode Switch Resistance vs Temperature
11 10 RESISTANCE () 9 8 7 6 ICPO = 100mA 1.9 VIN = 3.6V 1.8 RESISTANCE ()
1.5x Mode Charge Pump OpenLoop Output Resistance vs Temperature (1.5VIN - VCPO)/ICPO
VIN = 3V VCPO = 4.2V C1 = C2 = C6 = 1F
VCPO 20mV/DIV AC COUPLED
1.7 1.6 1.5 1.4 1.3
VIN = 3.6V 400ns/DIV ICPO = 80mA C1 = C2 = C6 = 1F
3230 G04
1.2 1.1 1.0 -40 -15 35 10 TEMPERATURE (C) 60 85
3230 G05
5 -40
-15
10 35 TEMPERATURE (C)
60
85
3230 G06
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LTC3230 TYPICAL PERFORMANCE CHARACTERISTICS
1.5x Mode CPO Voltage vs Load Current
4.8 4.6 CPO VOLTAGE (V) 4.4 4.2 4.0 3.8 3.6 0 50 100 150 LOAD CURRENT (mA) 200
3230 G07
2x Mode Charge Pump Open-Loop Output Resistance vs Temperature (2VIN - VCPO)/ICPO
12 11 RESISTANCE () 10 9 8 7 4.3 6 -40 -15 10 35 TEMPERATURE (C) 60 85
3230 G08
2x Mode CPO Voltage vs Load Current
5.1 5.0 4.9 CPO VOLTAGE (V) 4.8 4.7 4.6 4.5 4.4 VIN = 3.5V VIN = 3.4V VIN = 3.3V VIN = 3.2V VIN = 3.1V VIN = 3V VIN = 3.6V C1 = C2 = C6 = 1F
C1 = C2 = C6 = 1F VIN = 3.3V VIN = 3.4V VIN = 3.5V VIN = 3.6V
VIN = 3V VCPO = 4.8V C1 = C2 = C6 = 1F
VIN = 3.2V VIN = 3.1V VIN = 3V
4.2
0
100 50 150 LOAD CURRENT (mA)
200
3230 G09
MLED/SLED Pin Dropout Voltage vs MLED/SLED Pin Current
160 MLED/SLED DROPOUT VOLTAGE (mV) 140 120 FREQUENCY (kHz) 100 80 60 40 20 0 0 20 15 MLED/SLED PIN CURRENT (mA) 5 10 25
3230 G10
Oscillator Frequency vs VIN Voltage
1000 980 960 VIN CURRENT (A) 940 920 900 880 860 840 820 800 2.7 3.2 3.7 4.2 VIN (V) 4.7 5.2
3230 G11
VIN Shutdown Current vs VIN Voltage
5.0 4.5 4.0 TA = 25C TA = -40C TA = 85C
VIN = 3.6V
TA = 85C
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 2.7 3.7
TA = 25C TA = -40C
4.7 VIN (V)
3230 G12
1x Mode No-Load VIN Current vs VIN Voltage
580 560 SUPPLY CURRENT (mA) 540 VIN CURRENT (A) 520 500 480 460 440 420 400 2.8 3.2 3.6 4 VIN (V)
3230 G13
1.5x Mode Supply Current vs ICPO (IVIN - 1.5ICPO)
7 6 4 5 4 3 2 1 0 0 SUPPLY CURRENT (mA) VIN = 3.6V 5
2x Mode Supply Current vs ICPO (IVIN - 2ICPO)
VIN = 3.6V
RSET = 17.4k
3
2
1
4.4
4.8
5.2
0
100 50 LOAD CURRENT (mA)
150
3230 G14
0
100 50 LOAD CURRENT (mA)
150
3230 G15
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LTC3230 TYPICAL PERFORMANCE CHARACTERISTICS
MLED/SLED Pin Current vs MLED/SLED Pin Voltage
30 MLED/SLED PIN CURRENT (mA) 25 MLED/SLED CURRENT (mA) 20 15 10 5 0 0 0.04 0.08 0.12 0.16 MLED/SLED PIN VOLTAGE (V) 0.20
3230 G16
MLED/SLED Current vs ENM/ENS Strobe Pulses
25 VIN = 3.6V RSET = 17.7k EFFICIENCY (PLED/PIN) (%) 90 80 70 60 50 40 30 20 10 0 0 16 8 24 NUMBER OF STROBE PULSES 32
3230 G17
Efficiency vs VIN Voltage
VIN = 3.6V
20
15
10
5
C1 = C2 = C6 = 1F 5 LEDs AT 25mA/LED VF = 3.45V TA = 25C 2.7 3.1 3.5 3.9 VIN (V) 4.3 4.7
3230 G18
0
LDO2 Dropout Voltage vs Load Current
0.35 % CHANGE FROM NO LOAD (%) 0.30 DROPOUT VOLTAGE (V) 0.25 0.20 0.15 0.10 0.05 0 0 25 50 75 100 125 150 175 200 225 LOAD CURRENT (mA)
3230 G19
Output Voltage Accuracy vs Load Current
0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 0 25 50 75 100 125 150 175 200 LOAD CURRENT (mA)
3230 G20
LDO1 and LDO2 Load Transient Response
LDO2 50mV/DIV AC COUPLED LDO1 50mV/DIV AC COUPLED 60mA ILDO 50mA/DIV 10mA
CLDO = 1F
40s/DIV
3230 G21
Output Voltage Accuracy vs Temperature
0.05 0 % CHANGE FROM 25C (%) LDO CURRENT LIMIT (mA) -20 0 40 20 TEMPERATURE (C) 60 80
3230 G22
LDO1 and LDO2 Current Limit vs Temperature
500 475 450 425 400 375 350 -40 -20
-0.05 -0.10 -0.15 -0.20 -0.25 -0.30 -0.35 -0.40 -0.45 -40
0
20 40 60 80 TEMPERATURE (C)
100 120
3230 G23
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LTC3230 PIN FUNCTIONS
CPO (Pin 1): Output of the Charge Pump Used to Power All LEDs. This pin is enabled or disabled using the ENM and ENS inputs. A 1F X5R or X7R ceramic capacitor should be connected to ground. ENLDO1, ENLDO2 (Pins 2, 3): LDO1 and LDO2 Enables. Logic-level high enables LDO1 or LDO2. Logic-level low disables LDO1 or LDO2. RSET (Pin 4): LED Current Programming Resistor Pin. The RSET pin will servo to 0.8V. A resistor connected between RSET and GND is used to set the MLED and SLED full-scale current level. Connecting a resistor 10k or less will cause the LTC3230 to enter overcurrent shutdown. ENS, ENM (Pins 5, 11): SLED and MLED Enable and Output Control. The ENS and ENM pins are used to program the LED output currents. Pulse the ENS pin up to 31 times to decrement the internal 5-bit DAC which controls the Sub LED current from full scale to one LSB. Pulse the ENM pin up to 31 times to decrement the internal 5-bit DAC which controls the MLED1-4 LED currents from full scale to one LSB. The counters will stop at 1LSB when the number of strobes exceeds 31. The pin must be held high after the desired positive strobe edge and the data is transferred after a 150s (typical) delay. Holding the ENS or ENM pin low will clear the counter for the selected display and reset the LED current to zero. If both inputs are held low for longer than 150s (typical), the charge pump and LED current sources will go into shutdown. The charge pump mode is reset to 1x whenever ENS or ENM is held low or when the part is shut down. SLED (Pin 6): SLED Current Driver. SLED is the Sub current source output. The LED is connected between CPO (anode) and SLED (cathode). The current to the LED output is set via the ENS input. MLED1, MLED2, MLED3, MLED4 (Pins 7, 8, 9, 10): MLED1-4 Current Drivers. MLED1 to MLED4 are the Main current source outputs. The LEDs are connected between CPO (anodes) and MLED1-4 (cathodes). The current to the LED outputs are set via the ENM input. Any of the four LED outputs can be disabled by connecting the output directly to CPO. A 100A current will flow through each directly connected LED output. V2, V1 (Pins 12, 13): LDO Output Voltage Select. V1 is used to set LDO1's output voltage. V2 is used to set LDO2's output voltage. Tie to VIN, GND or float. LDO Output voltages set by V1 and V2 are shown below.
V1 LDO1 (V) V2 LDO2 (V) GND 1.2 GND 1.8 FLOAT 1.5 FLOAT 2.8 VIN 1.8 VIN 3.3
LDO2, LDO1 (Pins 14, 15): LDO Outputs. Bypass LDO1 and LDO2 with 1F X5R or X7R ceramic capacitors to GND. C2M, C1M, C2P, C1P (Pins 16, 17, 19, 20): Charge Pump Flying Capacitor Pins. 1F X5R or X7R ceramic capacitors should be connected from C1P to C1M and from C2P and C2M. VIN (Pin 18): Supply Voltage. This pin should be bypassed with a 2.2F or greater low ESR ceramic capacitor. Exposed Pad (Pin 21): Ground. This pad must be connected directly to a low impedance ground plane for proper thermal and electrical performance.
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LTC3230 BLOCK DIAGRAM
20 C1P 17 C1M 19 C2P 16 C2M GND 900kHz OSCILLATOR 18 VIN CPO 1 21
+ -
4 11 RSET ENM
50ns FILTER
5
ENS
50ns FILTER
3
ENLDO2
2
ENLDO1
13
V1
LDO1 VOUT SELECT LDO2 VOUT SELECT
12
V2
8
- +
0.8V TIMER 5-BIT DOWN COUNTER ENABLE MAIN 5-BIT LINEAR DAC MLED CURRENT SOURCES MLED1 7 MLED2 8 MLED3 9 MLED4 10 TIMER 5-BIT DOWN COUNTER TIMER ENABLE SUB 5-BIT LINEAR DAC SHUTDOWN SLED CURRENT SOURCES VIN SLED 6
+ -
LDO2 14
0.8V
+ -
LDO1 15
GND 21
3230 BD
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LTC3230 OPERATION
Power Management The LTC3230 uses a switched capacitor charge pump to boost CPO to as much as 2 times the input voltage up to 5V. The part starts up in 1x mode. In this mode, VIN is connected directly to CPO. 1x mode provides maximum efficiency and minimum noise. The LTC3230 will remain in 1x mode until any LED current source drops out. Dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. When dropout is detected, the LTC3230 will switch into 1.5x mode. The CPO voltage will then start to increase and will attempt to reach 1.5x VIN up to 4.5V. Any subsequent dropout will cause the part to enter 2x mode. The CPO voltage will attempt to reach 2x VIN up to 5V. The part will be reset to 1x mode whenever the part is shut down or when either ENM or ENS is driven low. A 2-phase non-overlapping clock activates the charge pump switches. In 2x mode the flying capacitors are charged on alternate clock phases from VIN to minimize CPO voltage ripple. In 1.5x mode the flying capacitors are charged in series during the first clock phase and stacked in parallel on VIN during the second phase. This sequence of charging and discharging the flying capacitors continues at a constant frequency of 900kHz. LED Current Control The MLED and SLED currents are delivered by programmable current sources controlled by the ENM and ENS
tPWH 200ns ENM OR ENS 200ns < tPWL < 20s LED CURRENT PROGRAMMED CURRENT
pins and by the value of the resistor on the RSET pin. There are four MLED current sources controlled by the ENM pin and one SLED current source controlled by the ENS pin. Full-scale current in the MLED and SLED pins are set by a resistor from the RSET pin to GND according to the following formula: MLED/SLED Full-Scale Output Current = 0.8 * 555 RSET T
Thirty two linear current settings are available by applying up to 31 pulses when enabling the ENM and ENS pins. Each strobe counts down a 5-bit DAC to set the LED current. When the desired count is reached, leave the enable strobe high and the output current will be set to the programmed value after a typical delay of 150s. If more than 31 strobes are received the counter will stop at one LSB. The output current will be set to zero if the enable is set low only after the 150s delay. If the enable is toggled before the 150s delay, the DAC counter will continue to count down and the current output will not be enabled until the start-up delay is finished. When both ENM and ENS are held low for more than 250s (minimum) the LED drivers and charge pump will go into shutdown. See Figure 1 for timing information. If the charge pump is in either 1.5x or 2x modes, the falling edge of either ENM or ENS will reset the charge pump to 1x mode.
tEN 250s
tSD 250s
SHUTDOWN
ENM = ENS = LOW
3230 F01
Figure 1. Current Programming Timing Diagram
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LTC3230 OPERATION
Charge Pump Soft-Start In shutdown, CPO is disconnected from VIN and is pulled down through a 14.3k resistor. When enabled, a weak switch connects VIN to CPO. This allows VIN to slowly charge the CPO output to prevent large charging currents. The LTC3230 also employs a soft-start feature on its charge pump to prevent excessive inrush current and supply droop when switching into the step-up modes. The current available to the CPO pin is increased linearly over a typical period of 50s. Soft-start occurs at the start of both 1.5x and 2x modes. Charge Pump Strength and Regulation Regulation is achieved by sensing the voltage at the CPO pin and modulating the charge pump strength based on the error signal. The CPO regulation voltages are set internally, and are dependent on the charge pump modes as shown in Table 1.
Table 1. Charge Pump Output Regulation Voltages
CHARGE PUMP MODE 1.5x 2x REGULATED VCPO 4.5V 5V
1.5 * VIN - CPO for 1.5x mode and 2 * VIN - CPO for 2x mode. Consider the example of driving white LEDs from a 3.1V supply. If the LED forward voltage is 3.8V and the current sources require 100mV, the advantage voltage for 1.5x mode is 3.1V * 1.5 - 3.8V - 0.1V or 750mV. Notice that if the input voltage is raised to 3.2V, the advantage voltage jumps to 900mV - a 20% improvement in available strength. From Figure 2, for 1.5x mode the available current is given by: IOUT = 1.5 * VIN - VCPO ROL
For 2x mode, the available current is given by: IOUT = 2 * VIN - VCPO ROL
Notice that the advantage voltage in this case is 3.1V * 2 - 3.8V - 0.1V = 2.3V. ROL is higher in 2x mode but a significant increase in available current is achieved. Typical values of ROL as a function of temperature are shown in Figures 3 and 4. Mode Switching The LTC3230 will automatically switch from 1x mode to 1.5x mode and subsequently to 2x mode whenever a dropout condition is detected at any LED pin. Dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. The time from dropout detection to mode switching is typically 0.5ms. The charge pump mode is reset back to 1x when the LED drivers are shut down (ENM = ENS = Low) or on the falling edge of either ENM or ENS. An internal comparator will not allow the main switches to connect VIN and CPO in 1x mode until the voltage at the CPO pin has decayed to less than or equal to the voltage at the VIN pin. LDO Operation Two independent low drop-out linear regulators are in the LTC3230. Each regulator may be independently enabled (ENLDO1 and ENLDO2) from each other and from the
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When the LTC3230 operates in either 1.5x mode or 2x mode, the charge pump can be modeled as a Thevenin equivalent circuit to determine the amount of current available from the effective input voltage and effective open-loop output resistance, ROL (Figure 2).
ROL
+
CPO
+ -
1.5VIN OR 2VIN
-
3230 F02
Figure 2. Charge Pump Thevenin Equivalent Open-Loop Circuit
ROL is dependent on a number of factors including the switching term, 1/(2 * fOSC * CFLY), internal switch resistances and the non-overlap period of the switching circuit. However, for a given ROL, the amount of current available will be directly proportional to the advantage voltage of
10
LTC3230 OPERATION
charge pump function. Driving ENLDO1 and ENLDO2 high enable LDO1 and LDO2 respectively. When the charge pump is enabled, each LDO consumes an additional 60A (typical) from VIN. If the charge pump is not enabled, one LDO consumes 125A (typical) and the second uses 60A (typical) additional current. LDO output voltage is set using three-level input pins V1 and V2 as shown in Table 2.
Table 2. LDO1 and LDO2 Output Voltage Control
V1 LDO1 (V) V2 LDO2 (V) GND 1.2 GND 1.8 FLOAT 1.5 FLOAT 2.8 VIN 1.8 VIN 3.3
The reference input to each LDO is ramped when enabled to provide an output soft-start lasting typically 100s. When an LDO is disabled its output is pulled to ground through an 11.5k resistor. Shutdown Current In shutdown mode all the circuitry is turned off and the LTC3230 draws a very low current from the VIN supply. When in shutdown, CPO is disconnected from VIN and is pulled to ground through a 14.3k resistor. The LTC3230 enters shutdown mode when both ENM and ENS pins are brought low for 250s (minimum) and ENLDO1 and ENLDO2 are brought low. All enable pins ENM, ENS, ENLDO1 and ENLDO2 have internal pull-downs to define the shutdown state whenever the inputs are floating.
11 10 RESISTANCE () 9 8 7 6
VIN = 3V VCPO = 4.2V C1 = C2 = C6 = 1F RESISTANCE ()
12 11 10 9 8 7
VIN = 3V VCPO = 4.8V C1 = C2 = C6 = 1F
5 -40
-15
10 35 TEMPERATURE (C)
60
85
3230 G06
6 -40
-15
10 35 TEMPERATURE (C)
60
85
3230 G08
Figure 3. Typical 1.5x ROL vs Temperature
Figure 4. Typical 2x ROL vs Temperature
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LTC3230 APPLICATIONS INFORMATION
VIN and CPO Capacitor Selection The style and value of the capacitors used with the LTC3230 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) ceramic capacitors are used on both VIN and CPO. Tantalum and aluminum capacitors are not recommended due to high ESR. The value of CCPO directly controls the amount of output ripple for a given load current. Increasing the size of CCPO will reduce the output ripple but will increase start-up time. The peak-to-peak output ripple of the 1.5x mode is approximately given by the expression: IOUT VRIPPLE(P-P) = 3 * fOSC * CCPO where fOSC is the oscillator frequency, typically 900kHz, and CCPO is the output storage capacitor. The output ripple in 2x mode is very small due to the fact that load current is supplied on both cycles of the clock. Both style and value of the output capacitor can significantly affect the stability of the LTC3230. As shown in the Block Diagram, the LTC3230 uses a control loop to adjust the strength of the charge pump to match the required output current. The error signal for the loop is stored directly on the output capacitor. The output capacitor also serves as the dominant pole for the control loop. To prevent ringing or instability, it is important for the output capacitor to maintain at least 0.6F of capacitance over all conditions. In addition, excessive output capacitor ESR >100m will tend to degrade the loop stability. Multilayer ceramic chip capacitors typically have exceptional ESR performance and when combined with a tight board layout will result in very good stability. As the value of CCPO controls the amount of output ripple, the value of CVIN controls the amount of ripple present at the input pin (VIN). The LTC3230's input current will be relatively constant while the charge pump is either in the input charging phase or the output charging phase but will drop to zero during the clock overlapping 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 LTC3230. 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 0.6F of capacitance for each of the flying capacitors. 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 -40C to 85C, whereas a Z5U or Y5V style capacitor will lose considerable capacitance over that range. Capacitors may also have a very 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 1F, 10V, Y5V ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22F, 10V, X7R available in the same case. The capacitor manufacturer's data sheet should be consulted to determine what value
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times. Since the nonoverlapping time is small (~10ns), 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 cause a higher input noise due to the higher ESR. Input noise can be further reduced by powering the LTC3230 through a very small series inductor as shown in Figure 5. A 10nH inductor will reject the fast current notches, thereby presenting a nearly constant current load to the input power supply.
VBAT LTC3230 GND
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Figure 5. 10nH Inductor Used for Input Noise Reduction
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LTC3230 APPLICATIONS INFORMATION
of capacitor is needed to ensure minimum capacitances at all temperatures and voltages. Table 3 shows a list of ceramic capacitor manufacturers and how to contact them.
Table 3. Recommended Capacitor Vendors
AVX Kemet Murata Taiyo Yuden Vishay xww.avxcrp.com www.kemet.com www.murata.com www.t-yuden.com www.vishay.com
* LED pads must be large and connected to the other layers of metal to ensure proper heat sinking. * The RSET pin is sensitive to noise and capacitance. The resistor should be placed near the part with minimum line width. Power Efficiency To calculate the power efficiency () of a white LED driver chip, the LED power should be compared to the input power. The difference between these two numbers represents lost power whether it is in the charge pump or the current sources. Stated mathematically, the power efficiency is given by: = PLED PIN
Layout Considerations and Noise Due to the high switching frequency and the transient currents produced by the LTC3230, careful board layout is necessary. A true ground plane and short connections to all capacitors will improve performance and ensure proper regulation under all conditions. The flying capacitor pins C1P, C2P, C1M and C2M will have high edge rate waveforms. The large dv/dt on these pins can couple energy to adjacent PCB runs. Magnetic fields can also be generated if the flying capacitors are not close to the LTC3230 (i.e., the loop area is large). To decouple capacitive energy transfer, a grounded PCB trace between the sensitive node and the LTC3230 pins will shield the sensitive node. For a high quality AC ground, the shield trace should be returned to a solid ground plane that extends all the way to the LTC3230. The following guidelines should be followed when designing a PCB layout for the LTC3230: * The Exposed Pad should be soldered to a large copper plane that is connected to a solid, low impedance ground plane using plated through hole vias for proper heat sinking and noise protection. * Input and output capacitors must be placed close to the part. * The flying capacitors must be placed close to the part. The traces from the pins to the capacitor pad should be as wide as possible. * VIN and CPO traces must be wide to minimize inductance and handle high currents.
The efficiency of the LTC3230 depends upon the mode in which it is operating. Recall that the LTC3230 operates as a pass switch, connecting VIN to CPO, until dropout is detected at a LED pin. This feature provides the optimum efficiency available for a given input voltage and LED forward voltage. When it is operating as a switch, the efficiency is approximated by: = PLED VLED * ILED VLED = = PIN VIN * IIN VIN
since the input current will be very close to the sum of the LED currents. At moderate to high output power, the quiescent current of the LTC3230 is negligible and the expression above is valid. Once dropout is detected at any LED pin, the LTC3230 enables the charge pump in 1.5x mode. In 1.5x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 1.5 times the actual input voltage. This is because the input current for a 1.5x charge pump is approximately 1.5 times the load current. In an ideal 1.5x charge pump, the power efficiency would be given by: = PLED V *I V = LED LED = LED PIN VIN * 1.5 * IIN 1.5 * VIN
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LTC3230 APPLICATIONS INFORMATION
In 2x boost mode as well, the efficiency is similar to that of a linear regulator with an effective input voltage of 2 times the actual input voltage. In an ideal 2x charge pump, the power efficiency would be given by: = PLED VLED * ILED V = = LED PIN VIN * 2 * IIN 2 * VIN Given a thermal resistance, JA, for the LTC3230 QFN package of 68C/W, at an ambient temperature of 70C the total power in the LTC3230 should be kept to less than 815mW. Applications in which the LDO output voltages are set to the lower range and which use a high VIN input voltage may require limiting the total current output to keep TJ less than 125C at the upper ambient temperature corners. An example using the parameters in Table 4 shows an application that just meets the maximum junction temperature limit. An increase in VIN, for example, will require reducing the output current of the charge pump or LDO.
Table 4. TJ Calculation Example Parameters
VIN Mode VLED ILEDTOTAL VLDO1 VLDO2 ILDO1 ILDO2 JA TA Total Power Dissipation Internal Junction Temperature 3.6V 1.5x 3.3V 100mA (20mA/LED) 1.5V 2.8V 200mA 200mA 68C/W 70C 799mW 124C
Thermal Management For higher input voltages and maximum output current, there can be substantial power dissipation in the LTC3230. If the junction temperature increases above approximately 150C the thermal shutdown circuitry will automatically deactivate the output current sources, charge pump and both LDOs. To reduce maximum junction temperature, a good thermal connection to the PC board is recommended. Connecting the Exposed Pad to a ground plane and maintaining a solid ground plane under the device will reduce the thermal resistance of the package and PC board considerably. Its built-in thermal shutdown circuitry will protect the LTC3230 from short term transient events. For continuous operation the maximum rated junction temperature is 125C. The power dissipated by the device is made up of three components: 1. The LTC3230 IVIN operating current (found in the Electrical Characteristics table) multiplied by VIN. PQ = IQ * VIN 2. The sum of the LED currents multiplied by the difference between VIN * Mode and the LED forward voltage where Mode is 1, 1.5 or 2 depending on the charge pump mode. PCP = (VIN * Mode - VLED) * ILEDTOTAL 3. For each LDO, the product of the LDO output current and the difference between VIN and the LDO. PLDO = (VIN - VLDO1) * ILDO1 + (VIN - VLDO2) * ILDO2
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LTC3230 PACKAGE DESCRIPTION
UD Package 20-Lead Plastic QFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1720 Rev A)
0.70 0.05 3.50 0.05 (4 SIDES)
1.65 0.05
2.10 0.05
PACKAGE OUTLINE 0.20 0.05 0.40 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED BOTTOM VIEW--EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 x 45 CHAMFER 19 20 0.40 0.10 1 2 1.65 0.10 (4-SIDES)
3.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6)
0.75 0.05 R = 0.05 TYP
R = 0.115 TYP
(UD20) QFN 0306 REV A
0.200 REF 0.00 - 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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
0.20 0.05 0.40 BSC
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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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LTC3230 TYPICAL APPLICATION
3-LED Main and One LED Sub at 20mA Full Scale
C1 1mF C2 1mF
VIN = 2.7V TO 5.5V
C3 2.2mF ENM ENS ENLDO1 ENLDO2
C1P C1M C2P C2M CPO VIN LTC3230 ENM ENS ENLDO1 ENLDO2 V1 V2 RSET MLED1 MLED2 MLED3 MLED4 SLED LDO1 LDO2
MAIN C6 1mF D1 D2 D3 MLED4 DISABLED 1.2V 3.3V C5 1mF C4 1mF
SUB D5
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RSET 21.5k ENM OR ENS
GND
SET BRIGHTNESS LEVEL
ON
OFF
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0108 REV A * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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