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AIC1880
Low Noise, Step-Up PWM DC/DC Converter
FEATURES
90% High Efficiency 1.6A, 0.3, 12V Internal Power MOSFET 640kHz/1.2MHz Pin-Selectable Operation Frequency 2.6V to 5.5V Input Range Low Shutdown Current: 0.1A Programmable Soft-Start External Compensation Network Adjustable Output from VIN to 11V Thin 8-Pin MSOP Package
DESCRIPTION
The AIC1880 is a step-up DC/DC converter with a 1.6A, 0.3 internal power switch. A soft-start programmed with an external capacitor sets the input current ramp rate. Pin-selectable high switching frequency (640kHz or 1.2MHz) allows easy filtering and low noises. An external compensation pin gives users flexibility in setting frequency compensation, which makes it feasible to use the small, low ESR ceramic output capacitors. The AIC1880 converts input ranging 2.6V to 5.5V into output voltage up to 11V. The device is available in a low profile 8-lead MSOP package.
APPLICATIONS
TFT Bias Supplies Handheld Devices PCMCIA Cards Portable Equipment
TYPICAL APPLICATION CIRCUIT
3.3V U1 VIN FREQ SHDN COMP L 6.8uH LX GND FB SS AIC1880 5 4 2 8 Css 0.022uF R2 220k SS24 Cout 10uF D 10V R1 1.6M
6 Cin 10uF 1.2MHz ON 640kHz OFF 7 3 1
Ccomp2 20pF
Rcomp 33k Ccomp 1200pF
Analog Integrations Corporation
Si-Soft Research Center 3A1, No.1, Li-Hsin Rd. I, Science Park, Hsinchu 300, Taiwan, R.O.C. TEL: 886-3-5772500, FAX: 886-3-5772510 www.analog.com.tw
DS-1880P-02
042507
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AIC1880
ORDERING INFORMATION
AIC1880PX XX PACKING TYPE TR: TAPE & REEL TB: TUBE PACKAGING TYPE O: MSOP-8 P: LEAD FREE COMMERCIAL Example: AIC1880POTR In MSOP-8 Package & Taping & Reel Packing Type PIN CONFIGURATION
MSOP-8 TOP VIEW
COMP 1 FB GND 2 4 SHDN 3
8 SS 7 FREQ 6 VIN 5 LX
ABSOLUTE MAXIMUM RATINGS
VIN, FB, SHDN , COMP, FREQ, SS to GND LX to GND Operating Ambient Temperature Range TA Operating Maximum Junction Temperature TJ Storage Temperature Range Lead Temperature (Soldering 10 Sec.) Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient (Assume no Ambient Airflow, no Heatsink) Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. MSOP-8 MSOP-8 -0.3 V to 5.5V -0.3 V to 12V -20C to 85C 125C -65C to 150C 260C 75C/W 180C/W
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AIC1880
ELECTRICAL CHARACTERISTICS
(TA=25C, VIN= SHDN =3V, FREQ=GND, unless otherwise specified) (Note 1)
PARAMETER Input Voltage Range Under Voltage Lock Out VFB=1.3V, not switching Quiescent Current Shutdown Current SOFT-START Soft-start current SWITCHING REGULATOR OSCILLATOR Frequency FREQ=GND FREQ=VIN Maximum Duty Cycle FREQ=GND FREQ=VIN Minimum Duty Cycle ERROR AMPLIFIER Feedback Voltage FB Input Bias Current FB Voltage Line Regulation Transconductance N-CHANNEL SWITCH Current Limit Internal Switch On-Resistance Leakage Current CONTROL INPUTS Input Low Voltage Input High Voltage Hysteresis FREQ Pull-Down Current
SHDN Input Current SHDN , FREQ
TEST CONDITION
SYMBOL
MIN 2.6 2.20
TYP 2.35 0.18 2 0.1
MAX 5.5 2.50 0.35 5 1
UNIT V V mA mA A A
VIN UVLO IIN IIN IIN
VFB=1V, switching
SHDN =GND
ISS
1.5
4
7
FOSC FOSC DC DC DC DC VFB IFB
540 1000
640 1220 85 85 16 30
740 1500
kHz kHz % % % %
FREQ=GND FREQ=VIN Level to produce VCOMP=1.24V VFB=1.24V Level to produce VCOMP=1.24V 2.6V < VIN < 5.5V I=5A
1.222
1.24 0 0.05
1.258 40 0.3
V nA %/V mhos A
GM
210 1.6 0.3 0.01 0.5 20
ILIM
ILX=1.2A VLX=12V RON ILXOFF
A
VIN=2.6V to 5.5V
SHDN , FREQ
VIL VIH 0.7VIN 0.1 VIN IFREQ I SHDN 1.8 5 0.1
0.3VIN
V V V
VIN=2.6V to 5.5V
SHDN , FREQ
9 1
A A
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AIC1880
Note 1: Specifications are production tested at TA=25C. Specifications over the -20C to 85C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC).
TYPICAL PERFORMANCE CHARACTERISTICS
95 90 85
95 90 85
fOSC = 1.2MHz L = 3.3H
fOSC = 640kHz L = 10H
EFFICIENCY (%)
80 75 70 65 60 55 50
EFFICIENCY (%)
fOSC = 640kHz L = 6.8H
80 75 70 65 60
fOSC = 1.2MHz L = 6.8H
VIN = 3.3V VOUT = 5V
1 10 100 1000
55 50
VIN = 3.3V VOUT = 10V
1 10 100 1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
Fig. 1 Efficiency at VIN=3.3V, VOUT=5V
Fig. 2 Efficiency at VIN=3.3V, VOUT=10V
)
95 90 85
0.9
NO-LOAD SUPPLY CURRENT (mA)
fOSC = 640kHz L = 10H fOSC = 1.2MHz L = 6.8H
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 2.5
EFFICIENCY (%)
80 75 70 65 60 55 50
fOSC = 640kHz
fOSC = 1.2MHz
VIN = 5V VOUT = 10V
1 10 100 1000
3.0
3.5
4.0
4.5
5.0
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
Fig. 3 Efficiency at VIN=5V, VOUT=10V
Fig. 4 No-Load supply current
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AIC1880
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
10.60 10.55 10.50
o
1600
OUTPUT VOLTAGE (V)
10.45 10.40 10.35 10.30 10.25 10.20 10.15 10.10 10.05 10.00 0 20 40
TA = +85 C
MAXIMUM CURRENT (mA)
1400 1200 1000 800 600 400 200
V OUT = 5V
TA = +25 C
o
V OUT = 10V
TA = -20 C
o
f OSC = 640kHz
3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
60
80
100 120 140 160 180 200 220 240 260
0 3.0
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
Fig. 5 Load regulation
Fig. 6 Maximum output current vs. Input voltage
IOUT IOUT
fOSC=640kHz L=10H COUT=32F RCOMP = 33k CCOMP = 1500pF CCOMP2 = 20pF fOSC=640kHz L=6.8H COUT=44F RCOMP = 62k CCOMP = 820pF CCOMP2 = 10pF
VOUT AC Couple
VOUT AC Couple
Fig. 7 Load-transient response at VIN=3.3V, VOUT=10V
Fig. 8 Load-transient response at VIN=3.3V, VOUT=5V
SHDN
SHDN
VOUT
VIN=3.3V VOUT=10V fOSC=640kHz IOUT=10mA COUT=32F
VOUT
VIN=3.3V VOUT=10V fOSC=640kHz IOUT=10mA COUT=32F CSS=4.7nF
IL
IL
Fig. 9 Startup waveform without soft-start
Fig. 10 Startup waveform with soft-start
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AIC1880
BLOCK DIAGRAM
SHDN
SHUTDOWN CONTROL
VIN SHUTDOWN UNDER VOLTAGE LOCK OUT UVLO SOFTSTART SS
COMP ERROR AMPLIFIER FB 1.24V CLOCK ERROR COMPARATOR CONTROL AND DRIVER LOGIC 1 N LX
GND FREQ OSCILLATOR CURRENT SENSE RSENSE SLOPE COMPENSATION
PIN DESCRIPTIONS
PIN 1: COMP PIN 2: FB PIN 3: SHDN - Compensation Pin for Error Amplifier. - Feedback Pin with a typical reference voltage of 1.24V. - Shutdown Control Pin. The Device will turn off when SHDN is Low. - Ground. - Switch Pin. - Power Supply Pin. PIN 8: SS PIN 7: FREQ - Frequency Select Pin. Oscillator frequency is 640kHz when FREQ connects to GND, and 1.2MHz when FREQ connects to VIN. - Soft-Start Control Pin. Connect a soft-start capacitor to this pin. A 4A constant current charges the soft-start capacitor. Leave open for no soft-start.
PIN 4:GND PIN 5: LX PIN 6: VIN
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AIC1880
COMPONENT SELECTION
VIN (V) 3.3 3.3 3.3 3.3 5.0 5.0 VOUT (V) 10 10 5 5 10 10 fOSC (Hz) 640k 1.2M 640k 1.2M 640k 1.2M L (H) 10 (Taiyo Yuden NP06D B100M) 6.8 (Taiyo Yuden NP06D B6R8M) 10 (Taiyo Yuden NP06D B100M) 4.7 (Taiyo Yuden NP06D B4R7M) 10 (Taiyo Yuden NP06D B100M) 6.8 (Taiyo Yuden NP06D B6R8M) COUT (F) 10 ceramic (Taiyo Yuden EMK325BJ106MN-B) 10 ceramic (Taiyo Yuden EMK325BJ106MN-B) 10 2 ceramic (Taiyo Yuden EMK325BJ106MN-B) 10 2 ceramic (Taiyo Yuden EMK325BJ106MN-B) 10 2 ceramic (Taiyo Yuden EMK325BJ106MN-B) 10 2 ceramic (Taiyo Yuden EMK325BJ106MN-B) RCOMP (k) 39 33 30 36 30 22 CCOMP (pF) 820 1200 820 1000 1200 1500 CCOMP2 (pF) 20 20 10 20 20 56 TYPICAL IOUT (MAX) (mA) 250 250 700 700 500 500
APPLICATION INFORMATION
Operation
The AIC1880 is a fixed-frequency and high efficiency step-up DC/DC converter with current-mode PWM control architecture. By selecting appropriate circuit components, it can achieve fast transient response. The AIC1880 can regulate its output voltage through a feedback control circuit, which is composed of an error amplifier; two comparators and several control signal generators. By comparing the voltage at FB pin to the reference voltage of 1.24, the error amplifier varies the voltage at COMP pin. The voltage at COMP pin is compared with the summing signal of current sensing signal and slope compensation signal to determine the duty cycle of internal power switch. In order to prevent overcharging the output capacitor and achieve better efficiency, AIC1880 will enter pulse-skipping mode (PSM) operation while working at light load conditions. switching frequency is 1.2MHz, as FREQ pin is connected to VIN. For 640kHz operation, an internal pull-low of FREQ pin allows the FREQ pin unconnected.
Current Limitation
Current limitation function of AIC1880 will be activated when the peak value of switch current reaches 1.6A (typ.). While the current limitation function is activated, the duty cycle will be reduced to limit the output power to protect the internal power switch.
Soft-Start
The AIC1880 provides the soft-start function. When
SHDN pin is connected to VIN, an internal current
source of 4A (typ.) charges an external soft-start capacitor. During the soft-start period, the voltage at SS pin will decide the allowable peak value of switch current. The peak value of switch current is 0A, when the voltage at SS pin is 0V. In addition, it is in full current limitation when the voltage at SS pin is higher than 1.0V. The soft-start time can be calculated in accordance with the following equation.
Frequency Selection
The AIC1880's switching frequency can be selected to be either 640kHz or 1.2MHz. The switching frequency is 640kHz, while FREQ pin is connected to GND. The
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AIC1880
1 .0 V 4A
t SS = C SS x
ciency. The forward drop voltage of a Schottky diode will result in the conduction losses in the diode, and the diode capacitance (CT or CD) will cause the switching losses. Therefore, it is necessary to consider both forward voltage drop and diode capacitance for diode selection. In addition, the rating of selected Schottky diode should be able to handle the output voltage and the maximum peak diode current. Input Capacitor To prevent the large input voltage ripple resulted from high frequency switching, the use of low ESR ceramic capacitor is recommended. A 10F ceramic capacitor is sufficient for most AIC1880 applications. Output Capacitor The selection of output capacitor depends on the required output voltage ripple. The output voltage ripple can be expressed as:
VOUT =
IOUT fOSC COUT
The soft-start capacitor is discharged to GND when the
SHDN pin is connected to GND.
Shutdown
By connecting the SHDN pin to GND, the AIC1880 can be shut down to reduce the supply current to 0.1A (typ.). At this operation mode, the output voltage of step-up converter is approximately equal to (VIN-VD). VD is the forward drop voltage of catch diode.
Components Selection
Inductor The inductor selection depends on the switching frequency and current ripple of inductor.
L VIN fOSC IL
V 1 - IN VOUT
The AIC1880's switching frequency can be selected to be either 640kHz or 1.2MHz. A higher switching frequency allows the use of a smaller inductance. However, higher switching frequency can cause more switching losses, resulting in lower efficiency. By setting the switching frequency and an acceptable current ripple of inductor, a suitable inductance can be obtained from above equation. In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor current in application to prevent core saturation. The peak value of inductor current can be calculated according to the following equation.
IPEAK = IIN(max ) +
V 1 - IN + ESR IL VOUT
For lower output voltage ripple, the use of low ESR ceramic capacitor is recommended. The tantalum capacitor can also be used well, but its ERS is larger than that of ceramic capacitor. Soft-Start Capacitor The soft-start of AIC1880 begins from VSS=0V and ends while VSS reaches 1.0V. During the soft-start period, an internal current source of 4A (typ.) charges the soft-start capacitor. Hence, the soft-start capacitor should be large enough to ensure that the output voltage has reached the regulation value before the soft-start function has finished.
VIN V 1 - IN 2 x fOSC L VOUT + VIN V 1 - IN 2 x fOSC L VOUT
=
IOUT(MAX ) VOUT
Output Voltage Programming By connecting a resistive divider R1 and R2, the output voltage of AIC1880 step-up converter can be set. VOUT can be calculated as:
VIN
Diode A Schottky diode with low forward drop voltage and fast reverse recovery is the ideal choice for better effi-
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AIC1880
R VOUT = 1.24 x 1 + 1 R 2
formance, it is necessary to adjust the component values of external compensation network.
The resistive divider should sit as close to FB pin as possible. Loop Compensation In order to avoid the poor output voltage ripple and low efficiency caused by instability, AIC1880 requires a proper external compensation network to compensate its feedback loop. In this external compensation network, RCOMP is used to set the high-frequency integrator gain for fast transient response. While RCOMP is decided, CCOMP is chosen to set the integrator zero to maintain the loop stability. CCOMP2 is used to cancel the zero caused by the output capacitor and its ESR. While using the ceramic capacitor as the output capacitor, CCOMP2 can be omitted due to the small ESR.
R COMP 10 x CCOMP COUT VOUT (k ) x L VIN
Layout Consideration
In order to ensure a proper operation of AIC1880, the following points should be managed comprehensively. 1. The input capacitor and VIN should be placed as close as possible to each other to reduce the input ripple voltage. 2. The output loop, which is consisted of the inductor, the internal power switch, the Schottky diode and the output capacitor, should be kept as small as possible. 3. The routes with large current should be kept short and wide. 4. Logically the large current on the converter should flow at the same direction. 5. The FB pin should be connected to the feedback resistors directly and the route should be away from the noise sources. 6. The soft-start capacitor should be connected to the SS pin and GND pin directly.
RL COUT (F) 10 x R COMP ESR x C OUT (F) R COMP
C COMP 2
For each components of external compensation network, the above equations provide the approximate calculations. In order to obtain better transient per-
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AIC1880
APPLICATION EXAMPLES
D4 BAT54S C10 0.1uF D3 BAT54S Vout2 28V/10mA C8 0.1uF D2 BAT54S C11 1uF C9 0.1uF C12 0.1uF C13 1uF Vout3 -9V/10mA
Vin 3.3V Cin 10uF 6 7 3 1
L1 U1 VIN FREQ SHDN COMP 6.8uH LX GND FB SS AIC1880 5 4 2 8 Css 0.047uF R2 220k SS12 Cout1 10uF D1 Vout1 10V/200m R1 1.6M
Ccomp2 20pF
Rcomp 36k Ccomp 1000pF
Fig. 11 TFT LCD Bias Supply at VIN=3.3V
D4 BAT54S C10 0.1uF D3 BAT54S Vout2 28V/10mA C11 1uF C9 0.1uF C8 0.1uF D2 BAT54S C12 0.1uF C13 1uF Vout3 -9V/10mA
Vin 5.0V Cin 10uF 6 7 3 1
L1 U1 VIN FREQ SHDN COMP 6.8uH LX GND FB SS AIC1880 5 4 2 8 Css 0.047uF SS12 Cout1 10uF D1 Vout1 10V/200mA R1 1.6M
Ccomp2 56pF
Rcomp 22k Ccomp 1500pF
R2 220k
Fig. 12 TFT LCD Bias Supply at VIN=5.0V
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AIC1880
PHYSICAL DIMENSIONS
MSOP-8
D
(unit: mm)
S Y M B O L
MSOP-8 MILLIMETERS MIN. MAX. 1.10 0.05 0.75 0.25 0.13 2.90 4.90 BSC 2.90 0.65 BSC 0.40 0 0.70 6 3.10 0.15 0.95 0.40 0.23 3.10
A A1 A2 b
E1
A A
E
A2
e
SEE VIEW B
c D
A
E E1 e L
b
A1
q
c
WITH PLATING
0.25 L
VIEW B
BASE METAL
SECTION A-A GAUGE PLANE SEATING PLANE
Note: 1. Refer to JEDEC MO-187AA. 2. Dimension "D" does not include mold flash, protrusions or gate burrs. Mold flash, protrusion or gate burrs shall not exceed 6 mil per side . 3. Dimension "E1" does not include inter-lead flash or protrusions. 4. Controlling dimension is millimeter, converted inch dimensions are not necessarily exact.
Note:
Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AIC product, nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
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