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20 V,1.2 MHz Step-Up DC-to-DC Switching Converter ADP1611
FEATURES
Fully integrated 1.2 A , 0.23 power switch Pin-selectable 700 kHz or 1.2 MHz PWM frequency 90% efficiency Adjustable output voltage up to 20 V 3% output regulation accuracy Adjustable soft start Input undervoltage lockout MSOP 8-lead package
GENERAL DESCRIPTION
The ADP1611 is a step-up dc-to-dc switching converter with an integrated 1.2 A, 0.23 power switch capable of providing an output voltage as high as 20 V. With a package height of less than 1.1 mm, the ADP1611 is optimal for space-constrained applications such as portable devices or thin film transistor (TFT) liquid crystal displays (LCDs). The ADP1611 operates in pulse-width modulation (PWM) current mode with up to 90% efficiency. Adjustable soft start prevents inrush currents at startup. The pin-selectable switching frequency and PWM current-mode architecture allow excellent transient response, easy noise filtering, and the use of small, cost-saving external inductors and capacitors. The ADP1611 is offered in the Pb-free 8-lead MSOP and operates over the temperature range of -40C to +85C.
APPLICATIONS
TFT LC bias supplies Portable applications Industrial/instrumentation equipment
FUNCTIONAL BLOCK DIAGRAM
COMP
1
IN
6
REF FB 2
ERROR AMP gm BIAS
ADP1611
F/F RAMP GEN COMPARATOR RT 7 SS 8 SD 3 OSC SOFT START CURRENTSENSE AMPLIFIER
4
5
SW
RQ S DRIVER
GND
Figure 1.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2005 Analog Devices, Inc. All rights reserved.
04906-001
ADP1611 TABLE OF CONTENTS
Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 4 ESD Caution.................................................................................. 4 Pin Configuration and Function Descriptions............................. 5 Typical Performance Characteristics ............................................. 6 Theory of Operation ...................................................................... 10 Current-Mode PWM Operation .............................................. 10 Frequency Selection ................................................................... 10 Soft Start ...................................................................................... 10 On/Off Control........................................................................... 10 Setting the Output Voltage ........................................................ 10 Choosing the Input and Output Capacitors ........................... 11 Diode Selection........................................................................... 12 Loop Compensation .................................................................. 12 Soft-Start Capacitor ................................................................... 13 Application Circuits ................................................................... 14 Step-Up DC-to-DC Converter with True Shutdown ............ 14 TFT LCD Bias Supply ................................................................ 14 SEPIC Power Supply .................................................................. 15 Layout Procedure ........................................................................... 16 Outline Dimensions ....................................................................... 18 Ordering Guide .......................................................................... 18
REVISION HISTORY
2/05--Revision 0: Initial Version
Rev. 0 | Page 2 of 20
ADP1611 SPECIFICATIONS
VIN = 3.3 V, TA = -40C to +85C, unless otherwise noted. All limits at temperature extremes are guaranteed by correlation and characterization using standard statistical quality control (SQC), unless otherwise noted. Table 1.
Parameter SUPPLY Input Voltage Quiescent Current Nonswitching State Shutdown Switching State1 OUTPUT Output Voltage Load Regulation Overall Regulation REFERENCE Feedback Voltage Line Regulation ERROR AMPLIFIER Transconductance Voltage Gain FB Input Bias Current SWITCH SW On Resistance SW Leakage Current Peak Current Limit2 OSCILLATOR Oscillator Frequency Maximum Duty Cycle SHUTDOWN Shutdown Input Voltage Low Shutdown Input Voltage High Shutdown Input Bias Current SOFT START SS Charging Current UNDERVOLTAGE LOCKOUT3 UVLO Threshold UVLO Hysteresis
1 2
Symbol VIN IQ IQSD IQSW VOUT
Conditions
Min 2.5
Typ
Max 5.5
Unit V A A mA V mV/mA % V %/V A/V dB nA
VFB = 1.3 V, RT = VIN VSD = 0 V fSW = 1.23 MHz, no load VIN ILOAD = 10 mA to 150 mA, VOUT = 10 V Line, load, temperature
390 0.01 1
600 10 2 20
0.05 3 1.212 -0.15 1.230 1.248 +0.15
VFB VIN = 2.5 V to 5.5 V gm AV I = 1 A VFB = 1.23 V RON ICLSET fOSC DMAX VIL VIH ISD RT = GND RT = IN COMP = open, VFB = 1 V, RT = GND ISW = 1.0 A VSW = 20 V
100 60 10 230 0.01 2.0 0.49 0.89 78 0.7 1.23 83 600 20
m A A MHz MHz % V V A A
0.885 1.6 90 0.6
2.2 VSD = 3.3 V VSS = 0 V VIN rising 2.2 0.01 3 2.4 220 2.5 1
V mV
This parameter specifies the average current while switching internally and with SW (Pin 5) floating. Guaranteed by design and not fully production tested. 3 Guaranteed by characterization.
Rev. 0 | Page 3 of 20
ADP1611 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter IN, COMP, SD, SS, RT, FB to GND SW to GND RMS SW Pin Current Operating Ambient Temperature Range Operating Junction Temperature Range Storage Temperature Range JA, Two Layers JA, Four Layers Lead Temperature Range (Soldering, 60 sec) Rating -0.3 V to +6 V 22 V 1.2 A -40C to +85C -40C to +125C -65C to +150C 206C/W 142C/W 300C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in combination. Unless otherwise specified, all other voltages are referenced to GND.
RC CC VOUT
1
IN
COMP
6
IN
CIN
R1 REF FB
2
ERROR AMP gm COMPARATOR F/F RAMP GEN RQ S BIAS
ADP1611
L1
R2
SW
5
D1 VOUT COUT
VIN 1.2MHz 700kHz SD 3 SS CSS
8
DRIVER
RT
7
OSC
SOFT START
CURRENTSENSE AMPLIFIER GND
04906-002
4
Figure 2. Block Diagram and Typical Application Circuit
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. 0 | Page 4 of 20
ADP1611 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
COMP 1 FB 2 SD 3 GND 4
8
SS RT IN SW
04906-0-003
ADP1611
TOP VIEW (Not to Scale)
7 6 5
Figure 3. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 Mnemonic COMP FB SD GND SW IN RT SS Description Compensation Input. Connect a series resistor-capacitor network from COMP to GND to compensate the regulator. Output Voltage Feedback Input. Connect a resistive voltage divider from the output voltage to FB to set the regulator output voltage. Shutdown Input. Drive SD low to shut down the regulator; drive SD high to turn it on. Ground. Switching Output. Connect the power inductor from the input voltage to SW and connect the external rectifier from SW to the output voltage to complete the step-up converter. Main Power Supply Input. IN powers the ADP1611 internal circuitry. Connect IN to the input source voltage. Bypass IN to GND with a 10 F or greater capacitor as close to the ADP1611 as possible. Frequency Setting Input. RT controls the switching frequency. Connect RT to GND to program the oscillator to 700 kHz, or connect RT to IN to program it to 1.2 MHz. Soft-Start Timing Capacitor Input. A capacitor from SS to GND brings up the output slowly at power-up.
Rev. 0 | Page 5 of 20
ADP1611 TYPICAL PERFORMANCE CHARACTERISTICS
100 VIN = 5V FSW = 700kHz L = 10H VOUT = 10V 90 VOUT = 20V 80 100 VIN = 3.3V FSW = 1.2MHz L = 4.7H VOUT = 13V VOUT = 5V 90
EFFICIENCY (%)
EFFICIENCY (%)
80
VOUT = 15V
VOUT = 8.5V 70 60
70
60
50 50
04906-004
40 1 10 100 LOAD CURRENT (mA)
30 1 10 100 LOAD CURRENT (mA)
1000
1000
Figure 4. Output Efficiency vs. Load Current
Figure 7. Output Efficiency vs. Load Current
100 VIN = 5V FSW = 1.2MHz L = 6.8H VOUT = 10V
2.8 VOUT = 10V 2.6 VIN = 5.5V 2.4
90 80
VOUT = 20V VOUT = 15V
CURRENT LIMIT (A)
EFFICIENCY (%)
2.2 2.0 1.8 1.6
VIN = 3.3V VIN = 2.5V
70 60
50 40 30 1 10 100 LOAD CURRENT (mA)
04906-005
1000
1.2 -40
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
Figure 5. Output Efficiency vs. Load Current
Figure 8. Current Limit vs. Ambient Temperature, VOUT = 10 V
95 90 85 VIN = 3.3V FSW = 700kHz L = 10H VOUT = 5V
1.4 RT = VIN
OSCILLATORY FREQUENCY (MHz)
VOUT = 13V
1.2
1.0 0.8 RT = GND 0.6 0.4 0.2 0 -40 VOUT = 10V VIN = 3.3V -15 10 35 AMBIENT TEMPERATURE (C) 60
EFFICIENCY (%)
80 VOUT = 8.5V 75 70 65 60
04906-006
55 50 1 10 100 LOAD CURRENT (mA)
1000
85
Figure 6. Output Efficiency vs. Load Current
Figure 9. Oscillatory Frequency vs. Ambient Temperature
Rev. 0 | Page 6 of 20
04906-009
04906-008
1.4
04906-007
40
ADP1611
1.4 RT = VIN
OSCILLATORY FREQUENCY (MHz)
0.50 FSW = 700kHz VFB = 1.3V 0.45
QUIESCENT CURRENT (mA)
1.2 1.0
0.40 VIN = 5.5V 0.35 VIN = 3.3V 0.30 VIN = 2.5V 0.25
04906-013
0.8 RT = GND 0.6 0.4 0.2 0 2.5 VOUT = 10V 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0
04906-010
5.5
0.20 -40
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
Figure 10. Oscillatory Frequency vs. Supply Voltage
Figure 13. Quiescent Current vs. Ambient Temperature
350 VIN = 5.5V VIN = 3.3V 250 VIN = 2.5V 200
QUIESCENT CURRENT (mA) SWITCH RESISTANCE (m)
0.60 FSW = 1.23kHz VFB = 1.3V 0.55
300
0.50
VIN = 5.5V
0.45 VIN = 3.3V 0.40 VIN = 2.5V 0.35
04906-014
150
04906-011
100 -40
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
0.30 -40
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
Figure 11. Switch Resistance vs. Ambient Temperature
Figure 14. Quiescent Current vs. Ambient Temperature
VIN = 3.3V
REGULATION FB VOLTAGE (V)
1.4 1.3 FSW = 700kHz VFB = 1V
1.242 1.2
SUPPLY CURRENT (mA)
1.1 1.0 0.9 0.8 0.7 0.6
VIN = 5.5V
1.232
VIN = 3.3V
1.222
04906-012
VIN = 2.5V
04906-015
0.5 0.4 -40 -15 10 35 AMBIENT TEMPERATURE (C) 60
1.212 -40
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
85
Figure 12. Regulation FB Voltage vs. Ambient Temperature
Figure 15. Supply Current vs. Ambient Temperature
Rev. 0 | Page 7 of 20
ADP1611
2.0 FSW = 1.23kHz VFB = 1V 250 300
1.8
SUPPLY CURRENT (mA)
1.6 VIN = 5.5V 1.4
UVLO HYS (mV)
04906-016
200
150
1.2 VIN = 3.3V 1.0 0.8 0.6 -40 VIN = 2.5V
100
50
04906-019
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
0 -40
-15
10 35 AMBIENT TEMPERATURE (C)
60
85
Figure 16. Supply Current vs. Ambient Temperature
Figure 19. UVLO Hysteresis vs. Ambient Temperature
1.0 0.9
SWITCH LEAKAGE CURRENT (A)
VIN = 3.3V SD = 0.4V VSW = 20V
3
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -40 15 70 AMBIENT TEMPERATURE (C)
04906-017
1 2
CH1 = IL 500mA/DIV CH2 = OUTPUT RIPPLE 100mV/DIV CH3 = SW 10V/DIV
VIN = 5V, VOUT = 20V, ILOAD = 200mA, FSW = 700kHz, L = 10H, COUT = 10F
125
CH1 10.0mV CH2 100mV CH3 10.0V
M2.00s T
A CH3
12.4V
0.00000s
Figure 17. Switch Leakage Current vs. Ambient Temperature
Figure 20. Switching Waveform in Continuous Conduction
1.2 VIN = 3.5V 1.0
SHUTDOWN THRESHOLD (V)
VIH
3
0.8 VIL 0.6
CH1 = IL 500mA/DIV CH2 = OUTPUT RIPPLE 100mV/DIV CH3 = SW 10V/DIV
VIN = 5V, VOUT = 20V, ILOAD = 20mA, FSW = 700kHz, L = 10H, COUT = 10F
0.4
1
0 -40
04906-018
15 70 AMBIENT TEMPERATURE (C)
125
CH1 10.0mV CH2 100mV CH3 10.0V
M2.00s
A CH3
12.2V
Figure 18. Shutdown Threshold vs. Ambient Temperature
Figure 21. Switching Waveform in Discontinuous Conduction
Rev. 0 | Page 8 of 20
04906-021
0.2
2
04906-020
ADP1611
2
4
CH1 = ILOAD 200mA/DIV CH2 = VOUT 200mV/DIV
VIN = 5V VOUT = 20V COUT = 10F L = 10H FSW = 700kHz RC = 400k CC = 100pF
CH1 = IL 2A/DIV CH2 = VOUT 10V/DIV CH3 = SD 1V/DIV CH4 = COMP 2V/DIV
2
VIN = 5V VOUT = 20V IOUT = 200mA CSS = 0F
1 1
04906-022
CH1 10.0mV CH2 200mV
M2.00s T
A CH1
4.8mV
3
571.200s
CH1 10.0mV CH2 10.0V CH4 2.00V CH3 1.00V
M200s
A CH3
680mV
Figure 22. Load Transient Response, 700 kHz, VOUT = 20 V
Figure 24. Start-Up Response from Shutdown, CSS = 0 F
4
2
CH1 = ILOAD 200mA/DIV CH2 = VOUT 200mV/DIV
VIN = 5V VOUT = 20V COUT = 10F L = 10H FSW = 1.2MHz RC = 400k CC = 100pF
2
CH1 = IL 2A/DIV CH2 = VOUT 10V/DIV CH3 = SD 1V/DIV CH4 = COMP 2V/DIV
VIN = 5V VOUT = 20V IOUT = 200mA CSS = 100nF
1
04906-023
1
CH1 10.0mV CH2 200mV
M200s T
A CH1
7.20mV
3
488.000s
CH1 10.0mV CH2 10.0V CH4 2.00V CH3 1.00V
M400s
A CH3
680mV
Figure 23. Load Transient Response, 1.2 MHz, VOUT = 20 V
Figure 25. Start-Up Response from Shutdown, CSS = 100 nF
Rev. 0 | Page 9 of 20
04906-025
04906-024
ADP1611 THEORY OF OPERATION
The ADP1611 current-mode step-up switching converter converts a 2.5 V to 5.5 V input voltage up to an output voltage as high as 20 V. The 1.2 A internal switch allows a high output current, and the high 1.2 MHz switching frequency allows tiny external components. The switch current is monitored on a pulse-by-pulse basis to limit it to 2 A.
ON/OFF CONTROL
The SD input turns the ADP1611 regulator on or off. Drive SD low to turn off the regulator and reduce the input current to 10 nA. Drive SD high to turn on the regulator. When the step-up dc-to-dc switching converter is turned off, there is a dc path from the input to the output through the inductor and output rectifier. This causes the output voltage to remain slightly below the input voltage by the forward voltage of the rectifier, preventing the output voltage from dropping to 0 when the regulator is shut down. Figure 28 shows the application circuit to disconnect the output voltage from the input voltage at shutdown.
CURRENT-MODE PWM OPERATION
The ADP1611 uses current-mode architecture to regulate the output voltage. The output voltage is monitored at FB through a resistive voltage divider. The voltage at FB is compared to the internal 1.23 V reference by the internal transconductance error amplifier to create an error current at COMP. A series resistorcapacitor at COMP converts the error current to a voltage. The switch current is internally measured and added to the stabilizing ramp, and the resulting sum is compared to the error voltage at COMP to control the PWM modulator. This currentmode regulation system allows fast transient response, while maintaining a stable output voltage. By selecting the proper resistor-capacitor network from COMP to GND, the regulator response is optimized for a wide range of input voltages, output voltages, and load conditions.
SETTING THE OUTPUT VOLTAGE
The ADP1611 features an adjustable output voltage range of VIN to 20 V. The output voltage is set by the resistive voltage divider (R1 and R2 in Figure 2) from the output voltage (VOUT) to the 1.230 V feedback input at FB. Use the following formula to determine the output voltage: VOUT = 1.23 x (1 + R1/R2) (1)
FREQUENCY SELECTION
The ADP1611 frequency is user-selectable and operates at either 700 kHz to optimize the regulator for high efficiency or at 1.2 MHz for small external components. Connect RT to IN for 1.2 MHz operation, or connect RT to GND for 700 kHz operation. To achieve the maximum duty cycle, which might be required for converting a low input voltage to a high output voltage, use the lower 700 kHz switching frequency.
Use an R2 resistance of 10 k or less to prevent output voltage errors due to the 10 nA FB input bias current. Choose R1 based on the following formula:
- 1.23 V R1 = R2 x OUT 1.23
(2)
INDUCTOR SELECTION
The inductor is an essential part of the step-up switching converter. It stores energy during the on time, and transfers that energy to the output through the output rectifier during the off time. Use inductance in the range of 1 H to 22 H. In general, lower inductance values have higher saturation current and lower series resistance for a given physical size. However, lower inductance results in higher peak current that can lead to reduced efficiency and greater input and/or output ripple and noise. Peak-to-peak inductor ripple current at close to 30% of the maximum dc input current typically yields an optimal compromise. For determining the inductor ripple current, the input (VIN) and output (VOUT) voltages determine the switch duty cycle (D) by the following equation: D=
SOFT START
To prevent input inrush current at startup, connect a capacitor from SS to GND to set the soft-start period. When the device is in shutdown (SD is at GND) or the input voltage is below the 2.4 V undervoltage lockout voltage, SS is internally shorted to GND to discharge the soft start capacitor. Once the ADP1611 is turned on, SS sources 3 A to the soft-start capacitor at startup. As the soft-start capacitor charges, it limits the voltage at COMP. Because of the current-mode regulator, the voltage at COMP is proportional to the switch peak current, and, therefore, the input current. By slowly charging the soft-start capacitor, the input current ramps slowly to prevent it from overshooting excessively at startup.
VOUT - VIN VOUT
(3)
Rev. 0 | Page 10 of 20
ADP1611
Table 4. Inductor Manufacturers
Vendor Sumida 847-956-0666 www.sumida.com Part CMD4D11-2R2MC CMD4D11-4R7MC CDRH4D28-100 CDRH5D18-220 CR43-4R7 CR43-100 DS1608-472 DS1608-103 D52LC-4R7M D52LC-100M L (H) 2.2 4.7 10 22 4.7 10 4.7 10 4.7 10 Max DC Current 0.95 0.75 1.00 0.80 1.15 1.04 1.40 1.00 1.14 0.76 Max DCR (m) 116 216 128 290 109 182 60 75 87 150 Height (mm) 1.2 1.2 3.0 2.0 3.5 3.5 2.9 2.9 2.0 2.0
Coilcraft 847-639-6400 www.coilcraft.com Toko 847-297-0070 www.tokoam.com
Using the duty cycle and switching frequency, fSW, determine the on time by the following equation: tON =
D f SW
(4)
The output capacitor maintains the output voltage and supplies current to the load while the ADP1611 switch is on. The value and characteristics of the output capacitor greatly affect the output voltage ripple and stability of the regulator. Use a low ESR output capacitor; ceramic dielectric capacitors are preferred. For very low ESR capacitors, such as ceramic capacitors, the ripple current due to the capacitance is calculated as follows. Because the capacitor discharges during the on time, tON, the charge removed from the capacitor, QC, is the load current multiplied by the on time. Therefore, the output voltage ripple (VOUT) is
The inductor ripple current (IL) in steady state is
V xt IL = IN ON L
Solving for the inductance value, L, L=
VIN x tON IL
(5)
(6)
VOUT =
Make sure that the peak inductor current (the maximum input current plus half the inductor ripple current) is below the rated saturation current of the inductor. Likewise, make sure that the maximum rated rms current of the inductor is greater than the maximum dc input current to the regulator. For duty cycles greater than 50%, which occur with input voltages greater than one-half the output voltage, slope compensation is required to maintain stability of the currentmode regulator. For stable current-mode operation, ensure that the selected inductance is equal to or greater than LMIN
QC I xt = L ON COUT COUT
(8)
where: COUT is the output capacitance. IL is the average inductor current. D V - VIN tON = and D = OUT f SW VOUT Choose the output capacitor based on the following equation:
C OUT
I L x (VOUT - V IN ) f SW x VOUT x VOUT
(9)
L > L MIN =
VOUT - V IN 1.8 A x f SW
(7) Table 5. Capacitor Manufacturers
Vendor AVX Murata Sanyo Taiyo-Yuden Phone No. 408-573-4150 714-852-2001 408-749-9714 408-573-4150 Web Address www.avxcorp.com www.murata.com www.sanyovideo.com www.t-yuden.com
CHOOSING THE INPUT AND OUTPUT CAPACITORS
The ADP1611 requires input and output bypass capacitors to supply transient currents while maintaining constant input and output voltage. Use a low equivalent series resistance (ESR) input capacitor, 10 F or greater, to prevent noise at the ADP1611 input. Place the capacitor between IN and GND as close to the ADP1611 as possible. Ceramic capacitors are preferred because of their low ESR characteristics. Alternatively, use a high value, medium ESR capacitor in parallel with a 0.1 F low ESR capacitor as close to the ADP1611 as possible.
Rev. 0 | Page 11 of 20
ADP1611
DIODE SELECTION
The output rectifier conducts the inductor current to the output capacitor and load while the switch is off. For high efficiency, minimize the forward voltage drop of the diode. For this reason, Schottky rectifiers are recommended. However, for high voltage, high temperature applications where the Schottky rectifier reverse leakage current becomes significant and can degrade efficiency, use an ultrafast junction diode. Make sure that the diode is rated to handle the average output load current. Many diode manufacturers derate the current capability of the diode as a function of the duty cycle. Verify that the output diode is rated to handle the average output load current with the minimum duty cycle. The minimum duty cycle of the ADP1611 is The regulator loop gain is
AVL =
VFB V x IN x GMEA x Z COMP x GCS x Z OUT VOUT VOUT
(12)
DMIN =
VOUT - VIN - MAX VOUT
where: AVL is the loop gain. VFB is the feedback regulation voltage, 1.230 V. VOUT is the regulated output voltage. VIN is the input voltage. GMEA is the error amplifier transconductance gain. ZCOMP is the impedance of the series RC network from COMP to GND. GCS is the current-sense transconductance gain (the inductor current divided by the voltage at COMP), which is internally set by the ADP1611. ZOUT is the impedance of the load and output capacitor. To determine the crossover frequency, it is important to note that, at that frequency, the compensation impedance (ZCOMP) is dominated by the resistor, and the output impedance (ZOUT) is dominated by the impedance of the output capacitor. So, when solving for the crossover frequency, the equation (by definition of the crossover frequency) is simplified to
V V 1 | A | = FB x IN x G xR xG x =1 VL V MEA COMP CS 2 x f x C V OUT OUT C OUT
(10)
where VIN-MAX is the maximum input voltage. Table 6. Schottky Diode Manufacturers
Vendor On Semiconductor Diodes, Inc. Central Semiconductor Sanyo Phone No. 602-244-6600 805-446-4800 631-435-1110 310-322-3331 Web Address www.onsemi.com www.diodes.com www.centralsemi.com www.sanyo.com
(13)
LOOP COMPENSATION
The ADP1611 uses external components to compensate the regulator loop, allowing optimization of the loop dynamics for a given application. The step-up converter produces an undesirable right-half plane zero in the regulation feedback loop. This requires compensating the regulator such that the crossover frequency occurs well below the frequency of the right-half plane zero. The righthalf plane zero is determined by the following equation:
V FZ ( RHP ) = IN V OUT R x LOAD 2 x L
2
where fC is the crossover frequency and RCOMP is the compensation resistor. Solving for RCOMP
R COMP = 2 x f C x C OUT x VOUT x VOUT V FB x V IN x G MEA x GCS
(14)
For VFB = 1.23, GMEA = 100 S, and GCS = 2 S
RCOMP = 2.55 x 10 4 x f C x COUT x VOUT x VOUT VIN
(15)
(11)
Once the compensation resistor is known, set the zero formed by the compensation capacitor and resistor to one-fourth of the crossover frequency, or
where: FZ(RHP) is the right-half plane zero. RLOAD is the equivalent load resistance or the output voltage divided by the load current. To stabilize the regulator, ensure that the regulator crossover frequency is less than or equal to one-fifth of the right-half plane zero and less than or equal to one-fifteenth of the switching frequency.
CCOMP =
2
x f C x RCOMP
(16)
where CCOMP is the compensation capacitor. The capacitor, C2, is chosen to cancel the zero introduced by output capacitance ESR. Solving for C2,
C2 = ESR x COUT RCOMP
(17)
Rev. 0 | Page 12 of 20
ADP1611
For low ESR output capacitance, such as with a ceramic capacitor, C2 is optional. For optimal transient performance, the RCOMP and CCOMP might need to be adjusted by observing the load transient response of the ADP1611. For most applications, the compensation resistor should be in the range of 30 k to 400 k, and the compensation capacitor should be in the range of 100 pF to 1.2 nF. Table 7 shows external component values for several applications.
ERROR AMP REF gm FB 2 RC CC
04906-026
SOFT-START CAPACITOR
The voltage at SS ramps up slowly by charging the soft-start capacitor (CSS) with an internal 3 A current source. Table 8 lists the values for the soft-start period, based on maximum output current and maximum switching frequency. The soft-start capacitor limits the rate of voltage rise on the COMP pin, which in turn limits the peak switch current at startup. Table 8 shows a typical soft-start period, tSS, at maximum output current, IOUT_MAX, for several conditions. A 20 nF soft-start capacitor results in negligible input current overshoot at startup, and so is suitable for most applications. However, if an unusually large output capacitor is used, a longer soft-start period is required to prevent input inrush current. Conversely, if fast startup is a requirement, the soft-start capacitor can be reduced or even removed, allowing the ADP1611 to start quickly, but allowing greater peak switch current (see Figure 24 and Figure 25).
COMP 1 C2
Figure 26. Compensation Components
Table 7. Recommended External Components for Popular Input/Output Voltage Conditions
VIN (V) 3.3 VOUT (V) 5 5 9 9 12 12 9 9 12 12 20 20 fSW (MHz) 0.70 1.23 0.70 1.23 0.70 1.23 0.70 1.23 0.70 1.23 0.70 1.23 L (H) 4.7 2.7 10 4.7 10 4.7 10 4.7 10 4.7 10 6.8 COUT (F) 10 10 10 10 10 10 10 10 10 10 10 10 CIN (F) 10 10 10 10 10 10 10 10 10 10 10 10 R1 (k) 30.9 30.9 63.4 63.4 88.7 88.7 63.4 63.4 88.7 88.7 154 154 R2 (k) 10 10 10 10 10 10 10 10 10 10 10 10 RCOMP (k) 50 90.9 71.5 150 130 280 84.5 178 140 300 400 400 CCOMP (pF) 520 150 820 180 420 100 390 100 220 100 100 100 IOUT_MAX (mA) 600 600 350 350 250 250 450 450 350 350 250 250
5
Table 8. Typical Soft Start Period
VIN (V) 3.3 VOUT (V) 5 5 9 9 12 12 COUT (F) 10 10 10 10 10 10 CSS (nF) 20 100 20 100 20 100 tSS (ms) 0.3 2 2.5 8.2 3.5 15 VIN (V) 5 VOUT (V) 9 9 12 12 20 20 COUT (F) 10 10 10 10 10 10 CSS (nF) 20 100 20 100 20 100 tSS (ms) 0.4 1.5 0.62 2 1.1 4.1
Rev. 0 | Page 13 of 20
ADP1611
APPLICATION CIRCUITS
The circuit in Figure 27 shows the ADP1611 in a step-up configuration. The ADP1611 is used here to generate a 15 V regulator with the following specifications: VIN = 3.5 V to 5.5 V VOUT = 15 V IOUT 400 mA The output can be set to the desired voltage using Equation 2. Use Equations 16 and 17 to change the compensation network.
L1 4.7H
TFT LCD BIAS SUPPLY
Figure 29 shows a power supply circuit for TFT LCD module applications. This circuit has +10 V, -5 V, and +22 V outputs. The +10 V is generated in the step-up configuration. The -5 V and +22 V are generated by the charge-pump circuit. During step-up , the SW node switches between 10 V and ground (neglecting forward drop of the diode and on resistance of the switch). When the SW node is high, C5 charges up to 10 V. C5 holds its charge and forward-biases D8 to charge C6 to -10 V. The Zener diode, D9, clamps and regulates the output to -5 V.
R4 200 C4 10nF R3 200 D5 D4 C3 10F VGH 22V D5 BZT52C22
5V
6
ADP1611
IN SD FB 2 RT SS GND
4
D1 SW 5 R1 112k R2 10k
15V
VGL -5V D9 BZT52C5VIS
BAV99 C5 10nF C6 D8 10F D7
ON
3
BAV99 D3 C2 1F
CIN 10F
7
8
COMP 1
CSS 22nF
04906-027
RCOMP 220k CCOMP 150pF
COUT 10F
L1 4.7H
C1 10nF D2 BAV99
3.3V
6
ADP1611
IN SD FB 2 RT SS GND
4
D1 SW 5 R1 71.3k R2 10k
10V
ON
3
Figure 27. 5 V to 15 V Step-Up Regulator
CIN 10F
7
8
COMP 1
Some battery-powered applications require very low standby current. The ADP1611 typically consumes 10 nA from the input, which makes it suitable for these applications. However, the output is connected to the input through the inductor and the rectifying diode, allowing load current draw from the input while shut down. The circuit in Figure 28 enables the ADP1611 to achieve output load disconnect at shutdown. To shut down the ADP1611 and disconnect the output from the input, drive the SD pin below 0.4 V.
4.7H
Figure 29. TFT LCD Bias Supply
The VGH output is generated in a similar manner by the charge-pump capacitors, C1, C2, and C4. The output voltage is tripled and regulated down to 22 V by the Zener diode, D5.
5V 10k
Q1
A
FDC6331
6
ADP1611
IN SHDN FB
2
15V SW 5 112k
3
Q1 B
7
10F
8
RT SS GND
4
10k COMP 1 220k
04906-028
10F
ON 22nF
150pF
Figure 28. Step-Up Regulator with True Shutdown
Rev. 0 | Page 14 of 20
04906-029
STEP-UP DC-TO-DC CONVERTER WITH TRUE SHUTDOWN
CSS 22nF
RCOMP 220k CCOMP 150pF
COUT 10F
ADP1611
SEPIC POWER SUPPLY
The circuit in Figure 30 shows the ADP1611 in a single-ended primary inductance converter (SEPIC) topology. This topology is useful for an unregulated input voltage, such as a batterypowered application in which the input voltage can vary between 2.7 V to 5 V, and the regulated output voltage falls within the input voltage range. The input and the output are dc-isolated by a coupling capacitor, C1. In steady state, the average voltage of C1 is the input voltage. When the ADP1611 switch turns on and the diode turns off, the input voltage provides energy to L1, and C1 provides energy to L2. When the ADP1611 switch turns off and the diode turns on, the energy in L1 and L2 is released to charge the output capacitor, COUT, and the coupling capacitor, C1, and to supply current to the load.
L1 4.7H C1 10F SW 5 R1 16.8k
2.5V-5.5V
6
ADP1611
IN SD RT SS GND
4
3.3V
ON
3
L2 4.7H FB 2 COMP 1 RCOMP 60k CCOMP 1nF
CIN 10F
7
8
COUT 10F R2 10k
04906-030
CSS 22nF
Figure 30. 3.3 V DC-to-DC Converter
Rev. 0 | Page 15 of 20
ADP1611 LAYOUT PROCEDURE
To achieve high efficiency, good regulation, and stability, a welldesigned printed circuit board layout is required. Where possible, use the sample application board layout as a model. Follow these guidelines when designing printed circuit boards (see Figure 1): * * * Keep the low ESR input capacitor, CIN, close to IN and GND. Keep the high current path from CIN through the inductor, L1, to SW and PGND as short as possible. Keep the high current path from CIN through L1, the rectifier, D1, and the output capacitor, COUT, as short as possible. * * * * Keep high current traces as short and as wide as possible. Place the feedback resistors as close to FB as possible to prevent noise pickup. Place the compensation components as close as possible to COMP. Avoid routing high impedance traces near any node connected to SW or near the inductor to prevent radiated noise injection.
Figure 31. Sample Application Board (Bottom Layer)
Rev. 0 | Page 16 of 20
04472-027
ADP1611
Figure 32. Sample Application Board (Top Layer)
Figure 33. Sample Application Board (Silkscreen Layer)
Rev. 0 | Page 17 of 20
04906-033
04472-028
ADP1611 OUTLINE DIMENSIONS
3.00 BSC
8 5
3.00 BSC
4
4.90 BSC
PIN 1 0.65 BSC 1.10 MAX 8 0 0.80 0.60 0.40
0.15 0.00 0.38 0.22 COPLANARITY 0.10
0.23 0.08 SEATING PLANE
COMPLIANT TO JEDEC STANDARDS MO-187AA
Figure 34. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
ORDERING GUIDE
Model ADP1611ARMZ-R71 ADP1611-EVAL
1
Temperature Range -40C to +85C
Package Description 8-Lead Mini Small Outline Package [MSOP] Evaluation Board
Package Option RM-8
Branding P11
Z = Pb-free part.
Rev. 0 | Page 18 of 20
ADP1611 NOTES
Rev. 0 | Page 19 of 20
ADP1611 NOTES
(c) 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04906-0-2/05(0)
Rev. 0 | Page 20 of 20

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