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Preliminary
RT9178
200mA, Ultra-Low Noise, Ultra-Fast CMOS LDO Regulator
General Description
The RT9178 is designed for portable RF and wireless applications with demanding performance and space requirements. The RT9178's performance is optimized for batterypowered systems to deliver ultra low noise and low quiescent current. A noise bypass pin is also available for further reduction of output noise. Regulator ground current increases only slightly in dropout, further prolonging the battery life. The RT9178 also works with low-ESR ceramic capacitors, reducing the amount of board space necessary for power applications, critical in hand-held wireless devices. The RT9178 consumes less than 0.01A in shutdown mode and has fast turn-on time less than 100S. The other features include ultra low dropout voltage, high output accuracy, current limiting protection, and high ripple rejection ratio. Available in the 5-lead SOT-25 package, the RT9178 also offers a range of 2.4V to 3.3V with 0.1V per step.
Features
Ultra-Low-Noise for RF Application Ultra-Fast Response in Line/Load Transient Quick Start-Up (Typically 100S) < 0.01A Quiescent Current When Shutdown Low Dropout: 200mV at 200mA Wide Operating Voltage Ranges: 2.5V ~ 6.0V TTL-Logic-Controlled Shutdown Input Low Temperature Coefficient Current Limiting Protection Thermal Shutdown Protection Only 1F Output Capacitor Required for Stability High Power Supply Rejection Ratio Custom Voltage Available
Applications
CDMA/GSM Cellular Handsets Battery-Powered Equipment Laptop, Palmtops, Notebook Computers Hand-Held Instruments PCMCIA Cards Portable Information Appliances
Ordering Information
RT9178Package Type B : SOT-25 Type I BR : SOT-25 Type II Operating Temperature Range C: Commercial Standard Output Voltage 24 : 2.4V 25 : 2.5V : : 33 : 3.3V
Pin Configurations
Part Number RT9178CB (Plastic SOT-25) Pin Configurations
TOP VIEW
5 4
1
2
3
1. 2. 3. 4. 5.
VIN GND SHDN BP OUT
RT9178CBR (Plastic SOT-25)
TOP VIEW
5 4
1
2
3
1. 2. 3. 4. 5.
OUT GND VIN SHDN BP
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.
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RT9178
Typical Application Circuit
VIN CIN 1F ON SHDN BP OFF RT9178 IN OUT GND
Preliminary
VOUT COUT 2.2F
CBP 10nF
Pin Description
Pin No. RT91781 5 2 3 4 CB RT91783 1 2 4 5 CBR Pin Name VIN VOUT GND SHDN BP Supply Input Regulator Output Common Ground Shutdown Input Logic, Active Low. If the shutdown feature is not required, connect SHDN to VIN. Reference Bypass, Connecting a 10nF capacitor to GND to reduce output noise. May be left open. Pin Function
Function Block Diagram
SHDN Quick Start Shutdown and Logic Control
IN
BP
VREF + _ Error Amp MOS Driver Current-Limit and Thermal Protection OUT
GND
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Preliminary Absolute Maximum Ratings (Note 1)
Supply Input Voltage Shutdown Input Voltage Power Dissipation, PD @ TA = 25C SOT-25 Package Thermal Resistance SOT-25, JA Lead Temperature (Soldering, 10 sec.) Junction Temperature Storage Temperature Range ESD Susceptibility (Note 2) HBM MM
RT9178
7V 7V 0.25W 250C/W 260C 150C -65C to 150C 2kV 200V
Recommended Operating Conditions (Note 3)
Supply Input Voltage Shutdown Input Voltage Junction Temperature Range 2.5V to 6V 0V to 6V -40C to 125C
Electrical Characteristics
(VIN = VOUT + 1V, CIN = 1F, COUT = 1F, CBP = 10nF, TA = 25C, unless otherwise specified) Parameter Output Voltage Accuracy Current Limit Quiescent Current (Note 6) Dropout Voltage (Note 4) Line Regulation Load Regulation (Note 5) Standby Current (Note 7) SHDN Input Bias Current Logic-Low Voltage SHDN Threshold Symbol VOUT ILIM IQ VDROP VLINE Test Conditions IOUT = 1mA RLOAD = 1 VSHDN 0.4V, IOUT = 0mA IOUT = 200mA VIN = (VOUT + 0.3V) to 6.0V, IOUT = 1mA Min -2 --------1.0 ----Typ -400 90 200 --0.01 0 --50 -70 -40 150 Max +2 -150 300 6 20 1 100 0.4 -----V VRMS dB C Units % mA A mV mV/V mV A nA
VLOAD 1mA < IOUT < 200mA ISTBY IIBSD VIL VSHDN = GND, Shutdown VSHDN = GND or VIN VIN = 3V to 5.5V, Shutdown VIN = 3V to 5.5V, Start-Up 10Hz to 100kHz, IOUT = 200mA COUT = 10F COUT = 10F, IOUT = 200mA
Logic-High Voltage VIH eNO f = 100Hz f = 10kHz PSRR TSD
Output Noise Voltage Power Supply Rejection Rate
Thermal Shutdown Temperature
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RT9178
Preliminary
Note 1. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and 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 affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. The human body model is a 100pF capacitor discharged through a 1.5K resistor into each pin. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. Dropout voltage is defined as the input to output differential at which the output voltage drops 2% below its nominal value measured at 1V differential. Note 5. Regulation is measured at constant junction temperature by using a 20mS current pulse. Devices are tested for load regulation in the load range from 1mA to 200mA. Note 6. Quiescent, or ground current, is the difference between input and output currents. It is defined by IQ = IIN - IOUT under no load condition (IOUT = 0mA). The total current drawn from the supply is the sum of the load current plus the ground pin current. Note 7. Standby current is the input current drawn by a regulator when the output voltage is disabled by a shutdown signal (VSHDN 0.4V). It is measured with VIN = 6V.
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Preliminary Typical Operating Characteristics
Output Voltage vs. Temperature
3.3 3.2
100 95
RT9178
Quiescent Current vs. Temperature
VIN = 4V CBP = 10nF CIN = 1F COUT = 1F
VIN = 4V CBP = 10nF
CIN = 1F COUT = 1F
Output Voltage (V)
3.1 3 2.9 2.8 2.7 -35 -15 5 25 45 65 85 105 125
Quiescent Current
90 85 80 75 70 -35 -15 5 25 45 65 85 105 125
Temperature (C)
Temperature (C)
0 -10 -20
PSRR
VIN = 4V CIN = 1F COUT = 1F CBP = 10nF TA = 25C
0 -10 -20
PSRR
VIN = 4V CIN = 1F COUT = 1F CBP = 10nF TA = -35C
PSRR(dB)
-40 -50 -60 -70 -80
PSRR (dB)
-30
100mA
-30 -40 -50 -60 -70 -80
100mA 1mA
1mA
-90 0.01
0.1
1
10
100
1000
-90 0.01
0.1
1
10
100
1000
Frequency (kHz)
Frequency (kHz)
0.3 0.25
Dropout Voltage
Line Transient (V)
VIN = 4V CIN = 1F COUT = 1F CBP = 10nF VIN = 3.2 to 3.8V CBP = 10nF 3.8 3.2
Line Transient
CIN = 1F COUT = 10F
Dropout Voltage (V)
TJ = +125C TJ = +25C
0.2 0.15 0.1 0.05 0 0
TJ = -35C
Output Voltage (mV)
200
20 0 -20
25
50
75
100
125
150
175
Load Current (mA)
Time: 500S/Div
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RT9178
Load Transient Load Transient (mA)
Preliminary
Load Transient Load Transient (mA)
VIN = 4.0V IOUT = 100mA to 200mA CBP = 10nF CIN = 1F, Ceramic COUT = 1F, Ceramic
100 0
VIN = 4.0V IOUT = 1mA to 100mA CBP = 10nF
CIN = 1F, Ceramic COUT = 1F, Ceramic
200 100
Output Voltage (mV)
20 0 -20
Output Voltage (mV)
20 0 -20
Time: 1mS/Div Start Up SHDN Input Voltage (V) SHDN Input Voltage (V)
6 4 2 0 3 2 1 0 VIN = 4.0V CBP = 10nF CIN = 1F, Ceramic COUT = 1F, Ceramic 6 4 2 0 3 3 2 1 0
Time: 1mS/Div Start Up
Output Voltage (V)
Output Voltage (V)
VIN = 4.0V CBP = 10nF CIN = 1F, Ceramic COUT = 10F, Ceramic
Time: 5S/Div Start Up SHDN Input Voltage (V)
6 4 2 150 100 VIN = 4.0V CBP = 10nF
Time: 10S/Div Noise
CIN = 1F, Ceramic COUT = 1F, Ceramic
Noise (V)
VIN = 4.0V CBP = 100nF CIN = 1F, Ceramic COUT = 1F, Ceramic
0 3
50 0 -50
Output Voltage (V)
2 1 0
-100
f = 10Hz to 100kHz
Time: 25S/Div
Time: 10mS/Div
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Preliminary Application Information
The RT9178 is ideal for mobile phone and similar battery-powered wireless applications. It provides up to 200mA, from a 2.5V to 6V input. Like any lowdropout regulator, the device requires input and output decoupling capacitors. These capacitors must be correctly selected for good performance (see Capacitor Characteristics Section). Please note that linear regulators with a low dropout voltage have high internal loop gains which require care in guarding against oscillation caused by insufficient decoupling capacitance. INPUT CAPACITOR An input capacitance of 1F is required between the device input pin and ground directly (the amount of the capacitance may be increased without limit). The input capacitor MUST be located less than 1 cm from the device to assure input stability (see PCB Layout Section). A lower ESR capacitor allows the use of less capacitance, while higher ESR type (like aluminum electrolytic) require more capacitance. Capacitor types (aluminum, ceramic and tantalum) can be mixed in parallel, but the total equivalent input capacitance/ESR must be defined as above to stable operation. There are no requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will be 1F over the entire operating temperature range. OUTPUT CAPACITOR The RT9178 is designed specifically to work with very small ceramic output capacitors. The recommended minimum capacitance (temperature characteristics X7R, X5R, Z5U, or Y5V) in 1F to 10F range with 5m to 50m range ceramic capacitor between LDO output and GND for transient stability, but it may be increased without limit. Higher capacitance values help to improve transient.
RT9178
The output capacitor's ESR is critical because it forms a zero to provide phase lead which is required for loop stability. REFERENCE BYPASS CAPACITOR (BP) Connecting a 10nF between the BP (reference bypass) pin and GND significantly reduces noise on the regulator output. It should be noted that the capacitor is connected directly to a high impedance circuit in the band gap reference. Because this circuit has only a few microamperes flowing into it, any significantly loading on this node will cause a change on the regulated output voltage. For this reason, DC leakage current through the noise bypass capacitor must never exceed 100nA, and should be kept as low as possible for best output voltage accuracy. The type of capacitors best suited for the noise bypass capacitor with either NP0 or C0G dielectric typically have very low leakage. 10nF polypropylene and polycarbonate film capacitors are available in small surface mount packages and typically have extremely low leakage current. NO LOAD STABILITY The device will remain stable and in regulation with no external load. This is specially important in CMOS RAM keep-alive applications. SHUTDOWN INPUT OPERATION The RT9178 is shutdown by pulling the SHDN pin low, and turned on by driving the input high. If the shutdown feature is not required, the SHDN pin should be tied to VIN to keep the regulator on at all times (the SHDN pin MUST NOT be left floating). To assure proper operation, the signal source used to drive the SHDN pin must be able to swing above and below the specified turn-on/off voltage thresholds listed in the "Electrical Characteristics" under VIH and VIL. The ON/OFF signal may comes from either CMOS output, or an open-collector output with pullup resistor to the device input voltage or another logic supply. The high-level voltage may exceed the device input voltage, but must remain within the absolute maximum ratings for the SHDN pin.
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RT9178
Preliminary
Aluminum electrolytics also typically have large temperature variation of capacitance value. Equally important to consider is a capacitor's ESR change with temperature: this is not an issue with ceramics, as their ESR is extremely low. However, it is very important in tantalum and aluminum electrolytic capacitors. Both show increasing ESR at colder temperatures, but the increase in aluminum electrolytic capacitors is so severe they may not be feasible for some applications. Ceramic: For values of capacitance in the 10F to 100 F range, ceramics are usually larger and more costly than tantalums but give superior AC performance for by-passing high frequency noise because of very low ESR (typically less than 10m). However, some dielectric types do not have good capacitance characteristics as a function of voltage and temperature. Z5U and Y5V dielectric ceramics have capacitance that drops severely with applied voltage. A typical Z5U or Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. The Z5U and Y5V also exhibit a severe temperature effect, losing more than 50% of nominal capacitance at high and low limits of the temperature range. X7R and X5R dielectric ceramic capacitors are strongly recommended if ceramics are used, as they typically maintain a capacitance range within 20% of nominal over full operating ratings of temperature and voltage. Of course, they are typically larger and more costly than Z5U/Y5U types for a given voltage and capacitance. Tantalum: Solid tantalum capacitors are recommended for use on the output because their typical ESR is very close to the ideal value required for loop compensation. They also work well as input capacitors if selected to meet the ESR requirements previously listed.
QUICK START-UP TIME The start-up time is determined by the time constant of the bypass capacitor. The smaller the capacitor value, the shorter the power up time, but less noise gets reduced. As a result, start-up time and noise reduction need to be taken into design consideration when choosing the value of the bypass capacitor. INPUT-OUTPUT (DROPOUT) VOLTAGE A regulator's minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Because the device uses a PMOS, its dropout voltage is a function of drain-to-source on-resistance, RDS(ON), multiplied by the load current: VDROUPOUT = VIN - VOUT = RDS(ON) x IOUT CURRENT LIMIT The RT9178 monitors and controls the PMOS' gate voltage, limiting the output current to 400mA (typ). The output can be shorted to ground for an indefinite period of time without damaging the part. SHORT-CIRCUIT PROTECTION The device is short circuit protected and in the event of a peak over-current condition, the short-circuit control loop will rapidly drive the output PMOS pass element off. Once the power pass element shuts down, the control loop will rapidly cycle the output on and off until the average power dissipation causes the thermal shutdown circuit to respond to servo the on/off cycling to a lower frequency. Please refer to the section on thermal information for power dissipation calculations. CAPACITOR CHARACTERISTICS It is important to note that capacitance tolerance and variation with temperature must be taken into consideration when selecting a capacitor so that the minimum required amount of capacitance is provided over the full operating temperature range. In general, a good tantalum capacitor will show very little capacitance variation with temperature, but a ceramic may not be as good (depending on dielectric type).
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Preliminary
Tantalums also have good temperature stability: a good quality tantalum will typically show a capacitance value that varies less than 10~15% across the full temperature range of 125C to -40C. ESR will vary only about 2X going from the high to low temperature limits. The increasing ESR at lower temperatures can cause oscillations when marginal quality capacitors are used (if the ESR of the capacitor is near the upper limit of the stability range at room temperature). Aluminum: This capacitor type offers the most capacitance for the money. The disadvantages are that they are larger in physical size, not widely available in surface mount, and have poor AC performance (especially at higher frequencies) due to higher ESR and ESL. Compared by size, the ESR of the aluminum electrolytic is higher than either tantalum or ceramic, and it also varies greatly with temperature. A typical aluminum electrolytic can exhibit an ESR increase of as much as 50X when going from 25C down to -40C. It should also be noted that many aluminum electrolytics only specify impedance at a frequency of 120Hz, which indicates they have poor high frequency performance. Only aluminum electrolytics that have an impedance specified at a higher frequency (between 20kHz and 100kHz) should be used for the device. Derating must be applied to the manufacturer's ESR specification, since it is typically only valid at room temperature. Any applications using aluminum electrolytics should be thoroughly tested at the lowest ambient operating temperature where ESR is the maximum. THERMAL CONSIDERATIONS The RT9178 series can deliver a current of up to 200mA over the full operating junction temperature range. However, the maximum output current must be derated at higher ambient temperature to ensure the junction temperature does not exceed 125C.
RT9178
With all possible conditions, the junction temperature must be within the range specified under operating conditions. Power dissipation can be calculated based on the output current and the voltage drop across regulator. PD = (VIN - VOUT) IOUT + VIN IGND The final operating junction temperature for any set of conditions can be estimated by the following thermal equation: PD (MAX) = ( TJ (MAX) - TA ) / JA Where TJ (MAX) is the maximum junction temperature of the die (125C) and TA is the maximum ambient temperature. The junction to ambient thermal resistance (JA) for SOT-25 package at recommended minimum footprint is 250C/W (JA is layout dependent). Visit our website in which "Recommended Footprints for Soldering Surface Mount Packages" for detail. PCB LAYOUT Good board layout practices must be used or instability can be induced because of ground loops and voltage drops. The input and output capacitors MUST be directly connected to the input, output, and ground pins of the device using traces which have no other currents flowing through them. The best way to do this is to layout CIN and COUT near the device with short traces to the VIN, VOUT, and ground pins. The regulator ground pin should be connected to the external circuit ground so that the regulator and its capacitors have a "single point ground". It should be noted that stability problems have been seen in applications where "vias" to an internal ground plane were used at the ground points of the device and the input and output capacitors. This was caused by varying ground potentials at these nodes resulting from current flowing through the ground plane. Using a single point ground technique for the regulator and it's capacitors fixed the problem. Since high current flows through the traces going into VIN
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RT9178
Preliminary
and coming from VOUT, Kelvin connect the capacitor leads to these pins so there is no voltage drop in series with the input and output capacitors. Optimum performance can only be achieved when the device is mounted on a PC board according to the diagram below:
BP
VOUT
VIN
GND
SHDN
SOT-25 (Type I) Board Layout
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Preliminary Package Information
RT9178
H D L C B
b A A1 e
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.889 0.000 1.397 0.356 2.591 2.692 0.838 0.102 0.356 Max 1.295 0.152 1.803 0.559 2.997 3.099 1.041 0.254 0.610
Dimensions In Inches Min 0.035 0.000 0.055 0.014 0.102 0.106 0.033 0.004 0.014 Max 0.051 0.006 0.071 0.022 0.118 0.122 0.041 0.010 0.024
SOT- 25 Surface Mount Package
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RT9178
Preliminary
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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