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Preliminary
RT9201
High Efficiency PWM Step-Down DC-DC Converter
General Description
The RT9201 is a high-efficiency pulse-width-modulated (PWM) step-down DC-DC converter. Capable of delivering 600mA output current over a wide input voltage range from 2.5 to 5.5V, the RT9201 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources within the range such as cellular phones, PDAs and handy-terminals. Four operational modes are available: PWM, PSM, LowDropout and shut-down modes. Internal synchronous rectifier with low RDS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical application. The RT9201 automatically turns off the synchronous rectifier while the inductor current is low and enters discontinuous PWM mode. This can increase efficiency at light load condition. The RT9201 enters PSM (pulse-skipping mode) at extremely light load condition. The equivalent switching frequency is reduced to increase the efficiency in PSM. The RT9201 enters Low-Dropout mode when normal PW M cannot provide regulated output voltage by continuously turning on the upper P-MOSFET. RT9201 enters shut-down mode and consumes less than 0.1A when EN pin is pulled low. The switching ripple is easily smoothed-out by small package filtering elements due to a fixed operation frequency of 800kHz. This along with small DFN package provides small PCB area application. Other features include soft start, 0.8V internal reference voltage with 1% accuracy, over temperature protection, and over current protection.
DFN-10L 3x3
EN SS FB NC GND
1 2 3 4 5
Features
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+2.5V to +5.5V Input Range Adjustable Output From 0.85V to VIN 600mA Output Current 95% Efficiency No Schottky Diode Required 85A Quiescent Current 100% Duty Cycle in Low-Dropout Mode 800kHz Fixed-Frequency PWM Operation Pulse-skipping Mode Operation During Light Ioad
Applications
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Cellular Telephones Wireless Modems Personal Information Appliances Portable Instruments Distributed Power Systems Battery-Powered Equipment (1 Li-Ion or 3 NiMH/NiCd)
Pin Configurations
(TOP VIEW)
10 9
GND
Ordering Information
RT9201
Marking Information
For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail.
DS9201-04 August 2004
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Package Type QV : DFN-10L 3x3 (V-Type) Operating Temperature Range P : Pb Free with Commercial Standard
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NC VDD 8 PVDD 7 LX PGND
9
RT9201
Typical Application Circuit
Preliminary
VIN CIN GPIO
8 PVDD 9 VDD RT9201 1 5 EN GND
LX
7
LX
VOUT RF1 COUT
FB 3 CF1 SS 2 PGND 6 CSS CF2
RF2
V OUT = 0.8 x
R F1 + R F2 R F2
Recommended using lower ESR capacitor
Recommended component selection for typical application circuit. VOUT (V) 0.85 1.375 1.5 1.8 2.5 3.3 VIN (V) 2.5 to 4.0 2.5 to 5.0 2.5 to 5.5 2.5 to 5.5 3.5 to 5.5 4.5 to 5.5 RF1 () 24k 280k 343k 487k 820k 1.2M CF1 (pF) 330 33 22 15 10 5.6 RF2 () 390k 390k 390k 390k 390k 390k CF2 (pF) 10 10 10 10 10 10 LX (H) 4.7 4.7 6.8 6.8 10 10 CSS (pF) 330 330 470 470 680 1000 CIN (uF) 10 10 10 10 10 10 COUT (uF) 22 or (10 x 2) 22 or (10 x 2) 22 or (10 x 2) 22 or (10 x 2) 22 or (10 x 2) 22 or (10 x 2)
Suggested Inductors Component Supplier Series Inductance (H) 4.7 SH4018 ABC SR0302 6.8 10 4.7 6.8 10 TDK SLF6028 4.7 6.8 10 4.7 Coilcraft DO1606 6.8 10 ESR (m) 82 100 150 150 180 250 28 35 53 150 200 300 Current Rating (mA) 1500 1150 1000 1200 1000 800 1600 1500 1300 1100 1000 900 6.5x5.23x2 6x6x2.8 3x2.8x2.5 4.8x4.8x1.8 Dimensions (mm)
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Preliminary
Suggested Capacitors For CIN and COUT Component Supplier TDK Panasonic Part No. C2012X5R0J106M C3225X5R0J226M ECJ2FB0J106M ECJHVB0J226M JMK212BJ106M TAIYO YUDEN JMK212BJ226MG JMK316BJ226ML Capacitance (uF) 10 22 10 22 10 22 22 Case Size 0805 1210 0805 1206 0805 0805 1206
RT9201
Function Block Diagram
VDD EN PVDD
OSC & Shutdown Control
Current Sense
Error Amplifier FB SS 300k 0.8V VREF
Slope Compensation
Control Logic
Driver
LX
PWM Comparator
Zero Detector
GND
PGND
Functional Pin Description
Pin Number Pin Name 1 2 3 4, 10 5 6 7 8 9 Exposed Pad EN SS FB NC GND PGND LX PVDD VDD GND Pin Function Tie this pin to 1.4V or higher to enable the device. Tie below 0.4V to shut-down. Soft Start, connect a capacitor from this pin to GND. Feedback Input pin. Connect a resistive voltage divider from the output voltage to FB to GND. No Connection Analog Ground Power Ground Switch node. Drains of the internal P-Channel and N-Channel MOSFET switches. Connect an inductor to LX pins together as close as possible. Main Power Supply Pin. Device Input Power Pin. Exposed pad should be soldered to PCB board and connected to GND
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RT9201
Absolute Maximum Ratings
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Preliminary
(Note 1)
Input Voltage ---------------------------------------------------------------------------------------------------------- 6V Power Dissipation, PD @ TA = 25C DFN-10L 3x3 --------------------------------------------------------------------------------------------------------- 2.1W Junction Temperature ---------------------------------------------------------------------------------------------- 150 C Storage Temperature Range -------------------------------------------------------------------------------------- -65C to 150C Package Thermal Resistance DFN-10L 3x3, JA --------------------------------------------------------------------------------------------------- 47 C/W Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------ 260 C Storage Temperature Range -------------------------------------------------------------------------------------- -65C to 150C ESD Susceptibility (Note 2) HBM (Human Body Mod) ----------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ----------------------------------------------------------------------------------------------- 200V
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Recommended Operating Conditions
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(Note 3)
Supply Input Voltage ------------------------------------------------------------------------------------------------ 2.5V to 5.5V Junction Temperature Range ------------------------------------------------------------------------------------- -40C to 125C
Electrical Characteristics
(VIN = 3.6V, VOUT = 2.5V, EN = VIN, LX = 10H, CIN = 10F, COUT = 22F, TA = 25 C, unless otherwise specified)
Parameter Input Voltage Range Adjustable Output Range Reference Voltage Cross Regulation FB Input Current PMOSFET RON NMOSFET RON P-Channel Current Limit Quiescent Current Shutdown Current Oscillator Frequency EN Input High Threshold EN Input Low Threshold Thermal Shutdown Temperature Maximum Duty Cycle Minimum On Time LX Leakage Current
Symbol VIN VOUT VREF VCROSS IFB (Note 4)
Test Conditions
Min 2.5 0.85 --3 -50 --0.8 ---1.5 -125
Typ --0.8 --0.37 0.3 -85 0.1 800 --150 -0.2 --
Max 5.5 VIN -+3 50 0.43 0.35 1.6 140 7 --0.4 --0.3 20
Units V V V % nA A A A kHz V V C % s A
IL = 300mA VIN = 2.5V to 5.5V, IL = 600mA to 0mA VFB = VIN
PRDS(ON) ILX = 200mA NRDS(ON) ILX = 200mA IP(LM) IQ IQ(SD) fOSC VIH VIL TSD VIN = VOUT No Load EN = 0V,VIN = 5.5V, VLX = 0V or VLX = 5.5V RL = 0.1 , VFB = VREF - 0.15 ILX = 0mA, VFB = VREF + 0.15 EN = 0V, VIN = 5.5V IOUT = 100mA VIN = 2.5V to 5.5V VIN = 2.5V to 5.5V
100 0.1 -20
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Preliminary
RT9201
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. Guarantee the VOUT range from 0.85V to V IN base on VOUT>0.3VIN.
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RT9201
Frequency vs. Temperature
820 810 800
Preliminary
Typical Operating Characteristics
Frequency vs. Input Voltage
830 825
Frequency (kHz)
790 780 770 760 750 740 730 -50 -25 0 25 50 75 100 125 150
Frequency (kHz)
VIN = 3.3V VOUT = 1.8V IOUT = 400mA
820 815 810 805 800 795 790 2 2.5 3 3.5 4 4.5 5 5.5 6
VOUT = 1.8V IOUT = 400mA
Temperature (C)
Input Voltage (V)
Output Voltage vs. Temperature
1.806 1.804 0.810 0.809 0.808
VFB vs. Temperature
Output Voltage (V)
1.802 1.800 1.798 1.796 1.794 1.792 1.790 -50 -25 0 25 50 75 100 125 150
V FB (V)
VIN = 3.3V VOUT = 1.8V IOUT = 200mA
0.807 0.806 0.805 0.804 0.803 -50 -25 0 25 50 75 100 125 150
Temperature (C)
Temperature (C)
Efficiency vs. Temperature
100 90 80 100 90 80
Efficiency vs. Output Current
VIN = 3.3V VOUT = 1.8V
Efficiency (%)
Efficiency (%)
70 60 50 40 30 20 10 0 -50 -25 0 25 50 75 100 125 150
70 60 50 40 30
VIN = 5V VOUT = 3.3V
VIN = 3.3V VOUT = 1.8V IOUT = 200mA
20 10 0 1 10 100 1000
Temperature (C)
Output Current (mA)
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Preliminary
RT9201
Output Voltage vs. Output Current
3.45 3.43
Output Voltage vs. Output Current
1.90
VIN = 3.3V VOUT = 1.8V
VIN = 5V VOUT = 3.3V
1.88
Output Voltage (V)
Output Voltage (V)
3.40 3.38 3.35 3.33 3.30 3.28
1.86
1.84
1.82
1.80 0 100 200 300 400 500 600 700 800
3.25 0 100 200 300 400 500 600 700 800
Output Current (mA)
Output Current (mA)
Minimum On-Time vs. Input Voltage
300 300
Minimum On-Time vs. Temperature
VIN = 3.3V VOUT = 1.8V IOUT = 0A
VOUT = 1.3V
Minimum On-Time (ns)
VOUT = 1.8V
200 150 100 50 0 2.5 3 3.5 4 4.5 5 5.5 6
Minimum On-Time (ns)
250
250 200 150 100 50 0 -50 -25 0 25 50 75
100
125
150
Input Voltage (V)
Temperature (C)
Current Limit vs. Input Voltage
1.14 1.12 1.10
Load Transient Response
100 VOUT (mV) 0 -100
Current Limit (A)
1.08 1.06 1.04 1.02 1.00 0.98 0.96 2 2.5 3 3.5 4 4.5 5 5.5 6
IOUT (mA)
500 0
VIN = 3.3V, VOUT = 1.8V IOUT = 0A to 600mA
Time (500s/Div)
Input Voltage (V)
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RT9201
Load Transient Response
Preliminary
Load Transient Response
100 VOUT (mV) 0 -100
300 to 0mA
100 VOUT (mV) 0 -100
IOUT (mA)
500 0
VIN = 3.3V, VOUT = 1.8V IOUT = 300 to 0mA
IOUT (mA)
500 0
VIN = 3.3V, VOUT = 1.8V IOUT = 300 to 600mA
Time (500s/Div)
Time (500s/Div)
Ripple & Noise
5 0 20 VOUT (mV) 0 IOUT (mA)
IOUT = 600mA
Load Transient Response
100 VOUT (mV) 0 -100
LX (V)
500 0
VIN = 5V, VOUT = 3.3V IOUT = 0 to 600mA
IOUT (mA)
500 0 VIN = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500s/Div)
Load Transient Response
100 VOUT (mV) 0 -100 VOUT (mV) 100 0 -100
Load Transient Response
IOUT (mA)
500 0
VIN = 5V, VOUT = 3.3V IOUT = 300 to 0mA
IOUT (mA)
500 0
VIN = 5V, VOUT = 3.3V IOUT = 300 to 600mA
Time (500s/Div)
Time (500s/Div)
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DS9201-04 August 2004
Preliminary
RT9201
Soft Start
5 0 2 0 500 0
VIN = 5V, VOUT = 3.3V IOUT = 0A CSS = 1000pF
Soft Start
5 0 2 0 500 0
VIN = 5V, VOUT = 3.3V IOUT = 0A CSS = 330pF
VEN (V) VOUT (V) IIN (mA)
VEN (V) VOUT (V) IIN (mA)
Time (200s/Div)
Time (200s/Div)
Soft Start
5 0 2 0 500 0
VIN = 5V, VOUT = 3.3V IOUT = 600mA CSS = 330pF
Soft Start
5 0 2 0
VEN (V) VOUT (V) IIN (mA)
VEN (V) VOUT (V)
500 IIN (mA) 0
VIN = 5V, VOUT = 3.3V IOUT = 600mA CSS = 1000pF
Time (200s/Div)
Time (500s/Div)
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RT9201
Application Information
Preliminary
A Zero Detector monitors inductor current by sensing voltage drop across the NMOSFET synchronous rectifier when it turns on. The NMOSFET turns off and allows the converter entering discontinuous conduction mode when the inductor current decreases to zero. The zero current defection on threshold is about 50mA.This reduces conduction loss and increase power conversion efficiency at light load condition. PSM Operation The minimum on-time of RT9201 is approximately 200ns. Consequently, the converter will enter pulse-skippingmode (PSM) during extreme light load condition or when modulation index (VOUT/VIN) is extreme low. This could reduce switching loss and further increase power conversion efficiency. For example : VIN = 3.8V, VOUT = 2.5V & ILOAD = 4mA Low Dropout Mode Operation The maximum on-time can exceed one oscillator cycle, which permits operation up to 100% duty cycle. As the input voltage drops, the duty cycle increases until the PMOSFET is held on continuously. Dropout voltage in 100% duty cycle is the output current multiplied by the on-resistance of the internal switch and inductor, around 300mV (IOUT = 600mA). When the converter operates around the boundary of Low-Dropout-Mode and PWM, sub-harmonic oscillation and large ripple may occur at output voltage as shown in Figure 1. Figure 2 illustrates the boundary of stable PWM and Low-Dropout-Mode operations for typical output voltages. Above each boudary is the stable PWM mode region with respect to that output voltage. To prevent subharmonic oscillation, please make sure that VIN and VOUT locate in the stable PWM operation region. If the input voltage range must cross the boundary region, increasing output capacitors with low ESR can alleviate the output ripple voltage.
RT9201 is a high-efficiency pulse-width-modulated (PW M) step-down DC-DC converter. Capable of delivering 600mA output current over a wide input voltage range from 2.5 to 5.5V, the RT9201 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources within the range such as cellular phones, PDAs and handyterminals. Chip Enable/Disable and Soft Start Four operational modes are available: PWM, PSM, LowDrop-Out and shut-down modes. Pulling EN pin lower than 0.4V shuts down the RT9201 and reduces its quiescent current to 0.1A. Pulling EN pin higher than 1.4V enables the RT9201 and initiates the softstart cycle. A softstart capacitor connected to SS pin along with the internal 300k resistor determines V REF ramp-up speed and the softstart behavior. A softstart capacitor between 330pF to 1000pF is recommended for smooth start-up of RT9201. PWM Operation During normal operation, the RT9201 regulates output voltage by switching at a constant frequency and then transferring the power to the load in each cycle by PWM. The RT9201 uses a slope-compensated, current-mode PWM controller capable of achieving 100% duty cycle. At each rising edge of the internal oscillator, the Control Logic cell sends a PWM ON signal to the Driver cell to turn on internal PMOSFET. This allows current to ramp up through the inductor to the load, and stores energy in a magnetic field. The switch remains on until either the current-limit is tripped or the PWM comparator signals for the output in regulation. After the switch is turned off, the inductor releases the magnetic energy and forces current through the NMOSFET synchronous rectifier to the output-filter capacitor and load. The output-filter capacitor stores charge when the inductor current is above the average output current and releases charge when the inductor current is below the average current to smooth the output voltage across the load.
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DS9201-04 August 2004
Preliminary
Sub-Harmonic at Boundary Condition
4
RT9201
due to over current or short circuit, it can build up only when output current is lower 50% of normal current limit threshold.
VLX (V)
2 0
Output Voltage Setting and Feedback Network The output voltage can be set from VREF to VIN by a voltage divider as:
100
VOUT = VREF x
RF1 + RF2 RF2
VOUT (mV)
0 -100 VIN = 3.8V, VOUT = 3.3V IOUT = 600mA, COUT = 100uF
The internal VREF is 0.8V with 1% accuracy. In practical application, keep R F2 = 390k and C F2 = 10pF respectively and choose appropriate R F1 and C F1 according to the required output voltage. Make sure that the product of RF1 and CF1 is about 8200k-pF. The following table shows recommended feedback network as well as inductor for some typical output voltages.
Time (10s/Div)
Figure 1
Boundary of PWM and Low-Dropout Mode Min. Input Voltage vs. Output Current
5.50 5.00
Table 1. Component Selection for Typical Application
PWM Mode VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V
VOUT (V) 0.85 1.5 2.5 3.3
RF1 () 24k 343k 820k 1.2M
CF1 (pF) 330 22 10 5.6
RF2 () 390k 390k 390k 390k
CF2 (pF) 10 10 10 10
LX (H) 4.7 6.8 10 10
CSS (pF) 330 470 680 1000
VIN(MIN) (V) Min. Input Voltage (V)
4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0 100 200 300 400 500 600 700
Low Dropout Mode
Inductor Selection The output inductor is suggested as the above table for optimal performance. Make sure that the inductor will not saturate over the operation conditions including temperature range, input voltage range, and maximum output current. If possible, choose an inductor with rated current higher than 1A so that it will not saturate even under circuit condition. Input Capacitor Selection The input capacitor can filter the input peak current and noise at input voltage source. The capacitor with low ESR (effective series resistance) provides the small drop voltage to stabilize the input voltage during the transient loading. For input capacitor selection, the ceramic capacitors larger than 10F is recommend. The capacitor must conform to the RMS current requirement. The maximum RMS ripple current is calculated as:
OutputOUT (mA) (mA) I Current
Figure 2 Over Current Protection The RT9201 continuously monitors the inductor current by sensing the voltage across the PMOSFET when it turns on. When the inductor current is higher than current limit threshold (1A typical), OCP activates and forces the PMOSFET turning off to limit inductor current cycle by cycle. The current limit is set to 50% level of normal condition when the output voltage is lower than its 50% normal level. This can minimize the power loss and protect the device when over current or output short circuit occurs. Once output voltage drops below to its 50% normal level
IRMS = IOUT(MAX)
VOUT (VIN - VOUT ) VIN
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DS9201-04 August 2004
RT9201
Output Capacitor Selection
Preliminary
The capacitor's ESR determines the output ripple voltage and the initial voltage drop following a high slew-rate transient's edge. Typically, if the ESR requirement is satisfied, the capacitance is adequate to filtering. The output ripple voltage can be calculated as: 1 VOUT = IC (ESR + ) 8 x COUT x fOSC The ceramic capacitor with low ESR value provides the low output ripple and low size profile. Connect a 22F ceramic capacitor at output terminal for good performance and place the input and output capacitors as close as possible to the device. Layout Considerations Follow the PCB layout guidelines for optimal performance of RT9201. 1. For the main current paths as indicated in bold lines in Figure 3, keep their traces short and wide. 2. Put the input capacitor as close as possible to the device pins (PVDD and PGND). 3. LX node is with high frequency voltage swing and should be kept small area. Keep analog components away from LX node to prevent stray capacitive noise pick-up. 4. Connect feedback network behind the output capacitors. Keep the loop area small. Place the feedback components near the RT9201. 5. Connect all analog grounds to a command node and then connect the command node to the power ground behind the output capacitors. 6. An example of 2-layer PCB layout is shown in Figure 4 to Figure 6 for reference.
R3 1 EN PVDD 9 VDD 10 4 5 NC RT9201 NC GND FB 3 LX 7 8 C9 L1 VOUT C7 C6 VDD
Figure 4. Top Layer
Figure 5. Bottom Layer
6 PGND SS 2 C4
R2
R1
Figure 6. Silkscreen Layer
C1
C2
Figure 3. RT9201 Layout Diagram
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Preliminary Outline Dimension
D2
RT9201
D
L
E
E2
1
e A A1 A3
b
Symbol A A1 A3 b D D2 E E2 e L
Dimensions In Millimeters Min 0.80 0.00 0.20 Ref. 0.18 3.00 2.20 3.00 1.40 0.50 0.20 0.50 1.75 2.70 0.30 Max 1.00 0.05
Dimensions In Inches Min 0.031 0.000 Max 0.039 0.002
0.008 Ref. 0.007 0.118 0.087 0.118 0.055 0.020 0.008 0.020 0.069 0.106 0.012
V-Type 10L DFN 3x3 Package
RICHTEK TECHNOLOGY CORP.
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
RICHTEK TECHNOLOGY CORP.
Taipei Office (Marketing) 8F-1, 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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