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Preliminary
RT9270
High Performance, Low Noise Boost Converter
General Description
The RT9270 is a high performance, low noise, fixed frequency step up DC-DC Converter. The RT9270 converters input voltage ranging 2.3V to 5.5V into output voltage up to 14V. Current mode control with external compensation network makes it easy to stabilize the system and keep maximum flexibility. Programmable soft start function minimizes impact on the input power system. Internal power MOSFET with very low RDS(ON) provides high efficiency. The RT9270 automatically transits from PWM to PSM (Pulse Skipping Mode) during light load condition further increasing efficiency. 670kHz and 1.3MHz operation frequency options provide flexibiltity of minimum output filter size, maximum efficiency and low BOM cost. The RT9270 also provides comprehensive protection functions such as UVLO, OCP, OTP, OVP and short circuit protection.
Features
90% Efficiency VIN Operating Range: 2.3V to 5.5V 1.9A, 0.25, 16V Internal Power MOSFET 670kHz and 1.3MHz Operation Frequency External Compensation Network Programmable Soft Start Function Small MSOP8 Package Short Circuit Protection , Thermal Shutdown, OVP are included RoHS Compliant and 100% Lead (Pb)-Free
Applications
TFT LCD panel OLED Display PCMCIA Cards Portable Device
Pin Configurations Ordering Information
RT9270 Package Type F : MSOP-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard)
COMP FB EN GND
8 2 3 4 7 6 5
(TOP VIEW)
SS FREQ VIN LX
MSOP-8
Note : RichTek Pb-free and Green products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. 100%matte tin (Sn) plating.
VIN C1
+
Typical Application Circuit
Chip Enable L1 D1 VOUT C2 R1
+
5 LX 6 VIN
GND EN
4 3 2 1 R3 C4
7 FREQ FB 8 SS COMP C5 RT9270
C3
R2
Figure 1
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RT9270
Function Block Diagram
Preliminary
EN COMP
LX VIN VFB 1.24 Error Amplifier 1.24V +
4uA Protection Enable SoftStart
VIN
SS LX N GND
FB
Summing Comparator + Clock
Control and Driver Logic
FREQ 5uA
Oscillator
Slope Compensation
Current Sense
Operation
The RT9270 is a high efficiency step-up Boost converter with a fixed-frequency, current-mode PWM architecture. It performs fast transient response and low noise operation with appropriate component selection. The output voltage is regulated through a feedback control consisting of an error amplifier, a summing comparator, and several control signal generators (as shown in function block diagram). The feedback reference voltage is 1.24V. The error amplifier varies the COMP voltage by sensing the FB pin. The slope compensation signal summed with the current -sense signal will be compared with the COMP voltage through the summing comparator to determine the current trip point and duty cycle. When driving light loads, the RT9270 will perform the pulse-skipping mode to prevent overcharging the output voltage. In this mode, the switching frequency will be reduced to perform a higher efficiency. Soft-Start The RT9270 provides soft-start function. When the EN pin is connected to high, a 4uA constant current is sourced to charge an external capacitor. The voltage rate of rise on the COMP pin is limited during the charging period, and so is the peak inductor current. When the EN pin is connected to GND, the external capacitor will be discharged to ground for the next time soft-start. Current Limitation The switch current is monitored to limit the value not to exceed 1.9A typically. When the switch current reaches 1.9A, the output voltage will be pulled down to limit the total output power to protect the power switch and external components. Shutdown Connect the EN to GND to turn the RT9270 off and reduce the supply current to 0.1uA. In this operation, the output voltage is the value of VIN to subtract the forward voltage of catch diode. Frequency Selection The switching frequency of RT9270 can be selected to operate at either 670kHz or 1.3MHz. When the FREQ pin is connected to GND for 670kHz operation, and connected to VIN for 1.3MHz operation. FREQ is preset to 670kHz operation for allowing the FREQ pin unconnected.
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Preliminary Pin Description
COMP (Pin 1) Compensation Pin for Error Amplifier. Connect a compensation network to ground. See the Component Selection Table for the loop compensation. FB (Pin 2) Feedback Pin. Connect an external resistor-divider tap to FB. The reference voltage is 1.24V and set VOUT according to: VOUT = 1.24V (1 + R1 / R2). See Figure 1. EN (Pin 3) Shutdown Control Input. Connect EN to GND to turn off the RT9270. GND (Pin 4) Ground. LX (Pin 5) Switch Pin. Connect the inductor and catch diode to LX pin. Widen and shorten the connected trace to minimize EMI. VIN (Pin 6) Supply Pin. Place at least a 1uF ceramic capacitor close to RT9270 for bypassing noise. FREQ (Pin 7) Frequency Select Pin. Oscillator frequency is 670kHz as FREQ connected to GND, and 1.3MHz as FREQ connected to VIN. A 5uA pull-down current is sinking on this pin. SS (Pin 8) Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. A 4uA constant current charges the soft-start capacitor. When EN connected to GND, the soft-start capacitor is discharged. When EN connected to VIN high, the soft-start capacitor is charged to VIN. Leave floating for not using soft-start.
RT9270
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RT9270
Absolute Maximum Ratings
Preliminary
(Note 1)
Supply Voltage, VIN --------------------------------------------------------------------------------------------------- -0.3 to 6V LX to GND --------------------------------------------------------------------------------------------------------------- - 0.3V to 16V The other pins ---------------------------------------------------------------------------------------------------------- - 0.3V to 6V Power Dissipation, PD @ TA = 70C MSOP-8 ----------------------------------------------------------------------------------------------------------------- 300mW Junction Temperature ------------------------------------------------------------------------------------------------- 150C Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260C Operation Temperature Range -------------------------------------------------------------------------------------- -40C to 85C Storage Temperature Range ---------------------------------------------------------------------------------------- - 65C to 150C ESD Susceptibility (Note 2) HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 3)
Ambient Temperature Range ---------------------------------------------------------------------------------------- 0C to 70C Junction Temperature Range ---------------------------------------------------------------------------------------- 0C to 125C
Electrical Characteristics
(VIN = 3V, FREQ left floating, TA = 25C, Unless Otherwise specification)
Parameter System Supply Input Operation voltage Range Under Voltage Lock Out Power On Reset Hysteresis Quiescent Current Shut Down Current Soft start Current Switching Regulator Oscillator Free Run Frequency fOSC FREQ=GND FREQ= VIN FREQ = GND FREQ = VIN VFB (Note 4) 2.3VMaximum Duty Cycle (Note 4) Reference Voltage Feedback Voltage Error Amplifier GM Feedback Voltage Line Regulation
1.216
1.24
1.264
V
---
1.1 0.12
--
ms
0.3 %/V To be continued
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Preliminary
Parameter MOSFET On Resistance of MOSFET Current Limitation R DS(ON) --250 1.9 Symbol Test Condition Min Typ
RT9270
Max 550 -Units m A
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. Guaranteed by Design.
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RT9270
Preliminary
Typical Operating Characteristics
Efficiency vs. Output Current
92 90 88 86
Efficiency vs. Output Current
92 90
L = 10uH, fOSC = 670kHz
L = 10uH, fOSC = 670kHz
88 86
Efficiency (%)
84 82 80 78 76 74 72 70
Efficiency (%)
84 82 80 78 76 74 72 70
L = 4.7uH, fOSC = 1.3MHz
L = 4.7uH, fOSC = 1.3MHz
VIN = 3.3V VOUT = 12V
1 10 100 1000
VIN = 5V VOUT = 12V
1 10 100 1000
Output Current (mA)
Output Current (mA)
760 740
Frequency vs. VIN
Frequency vs. VIN
1.6 1.5
Frequency (MHz)1
Frequency (kHz)1
720 700 680 660 640 620 600 2 3 4 5 6
1.4 1.3 1.2 1.1 1 2 3 4 5 6
VIN (V)
VIN (V)
Frequency vs. Temperature
900
Frequency vs. Temperature
1.50 1.45
800
1.40
Frequency (MHz)1
Frequency (kHz)1
1.35 1.30 1.25 1.20 1.15 1.10
700
600
500
400
VIN = 3.3V fOSC = 670kHz
-50 -30 -10 10 30 50 70 90 110 130
1.05 1.00
VIN = 3.3V fOSC = 1.3MHz
-50 -30 -10 10 30 50 70 90 110 130
Temperature (C)
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Temperature (C)
DS9270-09 March 2007
Preliminary
RT9270
VFB vs. Temperature
VFB vs. VIN
1.26 1.25 1.24
1.26 1.25 1.24
VFB (V)
VFB (V)
Ambient Temperature = 25C
1.23 1.22 1.21 1.20 2 2.5 3 3.5 4 4.5 5 5.5 6
1.23 1.22 1.21
VIN = 3.3V
1.20 -60 -40 -20 0 20 40 60 80 100
VIN (V)
Temperature (C)
Output Voltage vs. Output Current
12.1
No Load Supply Current vs. VIN
0.5
No Load Supply Current (mA) )
12.05 12
0.45 0.4
fosc = 1.3 MHz
Output Voltage (V)
11.95 11.9 11.85 11.8 11.75 11.7 11.65 0 30 60 90 120 150 180 210
fosc = 670kHz
0.35 0.3 0.25 0.2 2 2.5 3 3.5 4 4.5 5 5.5 6
VIN = 3.3V
Output Current (mA)
VIN (V)
Maximum Output Current vs. VIN
1600
Maximum Output Current vs. VIN
1600
Maximum Output Current (mA))
1400 1200 1000 800
Maximum Output Current (mA) )
TA = 25C,fosc = 670kHz VOUT = 7.2V
1400 1200 1000 800 600 400 200 0
TA = 25C,fosc = 1.3MHz
VOUT = 7.2V
VOUT = 12V
600 400 200 0 3 3.5 4 4.5 5 5.5 6
VOUT = 12V
3
3.5
4
4.5
5
5.5
6
VIN (V)
VIN (V)
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DS9270-09 March 2007
RT9270
Load-Transient Response
Load Current (200mA/Div) Output Voltage AC-Coupled (200mV/Div) Inductor Current (1A/Div)
VIN = 3.3V, VOUT = 12V R3 = 47k C3 = 1000pF C4 = 22pF
Preliminary
Load-Transient Response
Load Current (500mA/Div) Output Voltage AC-Coupled (200mA/Div) Inductor Current (1A/Div)
VIN = 3.3V, VOUT = 7.2V R3 = 22k C3 = 820pF C4 = 56pF
fOSC = 670kHz, L = 4.7uH, COUT = 33uF+0.1uF
fOSC = 670kHz, L = 4.7uH ,COUT = 47uF+0.1uF
Time (100us/Div)
Time (100us/Div)
Startup Waveform Without Soft-Start
VIN= 3.3V, VOUT= 12V, IOUT= 10mA
Startup Waveform With Soft-Start
VIN = 3.3V, VOUT= 12V, IOUT= 10mA
EN (2V/Div) Output Voltage (5V/Div) Inductor Current (1A/Div)
EN (2V/Div) Output Voltage (5V/Div) Inductor Current (500mA/Div)
fOSC = 670kHz, NO Soft-Start Capacitor
fOSC = 670kHz, CSS = 0.027uF
Time (200us/Div)
Time (1ms/Div)
Startup Waveform With Soft-Start
VIN = 3.3V, VOUT= 12V, IOUT= 100mA
Switching Waveform
LX Switching Waveform (5V/Div) Output Voltage AC-Coupled (200mV/Div) Inductor Current (1A/Div)
VIN = 3.3V, VOUT= 12V, IOUT= 200mA fOSC = 670kHz, L = 10uH, COUT = 33uF+0.1uF
EN (2V/Div) Output Voltage (5V/Div) Inductor Current (500mA/Div)
fOSC = 670kHz, CSS = 0.027uF
Time (1ms/Div)
Time (400ns/Div)
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Preliminary
RT9270
OTP Waveform
VIN = 3.3V, VOUT = 12V, IOUT= 400mA
OCP Waveform
Output Current (500mA/Div) Inductor Current (1A/Div) Output Voltage (10V/Div) LX Switching Waveform (10V/Div)
VIN = 3.3V, VOUT = 12V, IOUT= 400mA
LX Switching Waveform (5V/Div)
fOSC = 670kHz, ILIMIT = 1.9A
Inductor Current (1A/Div)
fOSC = 1.3MHz, ILIMIT = 1.9A
Time (2ms/Div)
Time (4ms/Div)
Maximum Output Current vs. Temperature
800
Maximum Output Current (mA) )
VIN = 3.3V,L = 4.7uH,fOSC = 1.3MHz
700 600 500 400 300 200 100 0 -60 -40 -20 0 20 40 60 80
VOUT= 7.2V
VOUT= 12V
Temperature (C)
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RT9270
Component Selection Table
VIN (V) 3.3 3.3 3.3 3.3 3.3 3.3 VOUT (V) 12 12 12 12 7.2 7.2 fOSC (Hz) 670k 670k 1.3M 1.3M 670k 1.3M L1 (uH) 10(TDK SLF6028) 4.7(TDK SLF6028) 10(TDK SLF6028) 4.7(TDK SLF6028) 4.7(TDK SLF6028) 4.7(TDK SLF6028)
Preliminary
C2 (uF) 33 tantalum 33 tantalum 33 tantalum 33 tantalum 47 tantalum 47 tantalum
R3 (k ) 36 47 39 51 22 32
C3 (pF) 1200 1000 1000 820 820 1000
C4 (pF) 33 22 33 22 56 56
Typical IOUT(MAX) (mA) 250 250 210 210 490 450
Application Information
The design procedure of Boost converter can start from the maximum input current, which is related about inductor, catch-diode, input/output capacitor selections and the maximum power which internal switch can stand. It can be derived from maximum output power, minimum input voltage and the efficiency of Boost converter. Once the maximum input current is calculated, the inductor value can be determined and the other components as well. Inductor Selection For a better efficiency in high switching frequency converter, the inductor selection has to use a proper core material such as ferrite core to reduce the core loss and choose low ESR wire to reduce copper loss. The most important point is to prevent the core saturated when handling the maximum peak current. Using a shielded inductor can minimize radiated noise in sensitive applications. The maximum peak inductor current is the maximum input current plus the half of inductor ripple current. The calculated peak current has to be smaller than the current limitation in the electrical characteristics. A typical setting of the inductor ripple current is 20% to 40% of the maximum input current. If the selection is 40%, the maximum peak inductor current is :
IPK = IIN(MAX) + = 1.2 x [ 1 2 IRIPPLE = 1.2 x IIN(MAX) ]
The minimum inductance value is derived from the following equation :
L= x VIN(MIN) x [VOUT - VIN(MIN)] 0.4 x IOUT(MAX) x VOUT x fOSC
2 2
Depending on the application, the recommended inductor value is between 2.2uH and 10uH. Diode Selection To achieve high efficiency, Schottky diode is good choice for low forward drop voltage and fast switching time. The output diode rating should be able to handle the maximum output voltage, average power dissipation and the pulsating diode peak current. Input Capacitor Selection For better input bypassing, low-ESR ceramic capacitors are recommended for performance. A 10uF input capacitor is sufficient for most applications. For a lower output power requirement application, this value can be decreased. Output Capacitor Selection For lower output voltage ripple, low-ESR ceramic capacitors are recommended. The tantalum capacitors can be used as well, but the ESR is bigger than ceramic capacitor. The output voltage ripple consists of two components: one is the pulsating output ripple current flows through the ESR, and the other is the capacitive ripple caused by charging and discharging.
IOUT(MAX) x VOUT x VIN(MIN)
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DS9270-09 March 2007
Preliminary
VRIPPLE = VRIPPLE(ESR) + VRIPPLE(C) IPEAK x ESRCOUT + IPEAK COUT VOUT x fOSC ( VOUT - VIN ) Soft-Start Capacitor
RT9270
Output Voltage The regulated output voltage is calculated by :
VOUT = 1.24V x (1+ R1 R2 )
The soft-start function begins from VSS=0V to VSS=1.24V with a 4uA constant current charging to the soft-start capacitor, so the capacitor should be large enough to let the output voltage reach regulation inside the soft-start cycle. Typical value of soft-start capacitor range is from 10nF to 200nF. After the cycle finished, the load can start to draw maximum current as required. Layout Guideline For high frequency switching power supplies, the PCB layout is important step in system application design. In order to let IC achieve good regulation, high efficiency and stability, it is strongly recommended the power components should be placed as close as possible. These traces should be wide and short. The feedback pin and the networks of feedback and compensation should be kept away from the power loops, and be shielded with a ground trace or plane to prevent noise coupling.
For most applications, R2 is a suggested a value up to 100k. Place the resistor-divider as close to the IC as possible to reduce the noise sensitivity. Loop Compensation The RT9270 voltage feedback loop can be compensated with an external compensation network consisted of R3, C3 and C4 (As shown in Figure 1). Choose R3 to set the high-frequency integrator gain for fast transient response without over or under compensation. Once R3 is determined, C3 is selected to set the integrator zero to maintain loop stability. The purpose of C4 is to cancel the zero caused by output capacitor and the capacitor ESR. If the ceramic capacitor is selected to be the output capacitor, C4 can be taken off because of the small ESR. C2 is the output capacitor as shown in Figure 1. The following equations give approximate calculations of each component :
C3 = 2 C2 x RL x 10
-12
(F)
R3 =
VO x L1x C2 2 x C3 x VIN
()
C4 = C2 x RESR x 1x 10
-6
(F)
The best criterion to optimize the loop compensation is by inspecting the transient response and adjusting the compensation network.
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RT9270
L1 VIN
Preliminary
D1
+
VOUT C2 C6 R1 S1 C3 C4 R3 R2
C1
5 LX 6 VIN
GND
4 3
+
S2 C5
EN 7 FREQ FB 2 8 SS COMP 1 RT9270
EVB Circuit
Top Side
Bottom Side
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DS9270-09 March 2007
Preliminary Outline Dimension
D L
RT9270
E
E1
e A A1 b A2
Symbol A A1 A2 b D e E E1 L
Dimensions In Millimeters Min 0.810 0.000 0.750 0.220 2.900 0.650 4.800 2.900 0.400 5.000 3.100 0.800 Max 1.100 0.150 0.950 0.380 3.100
Dimensions In Inches Min 0.032 0.000 0.030 0.009 0.114 0.026 0.189 0.114 0.016 0.197 0.122 0.031 Max 0.043 0.006 0.037 0.015 0.122
8-Lead MSOP Plastic Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
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