LM8801 NSC | Alldatasheet
Document overview
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Technical content
Features
■ Over 90% efficiency at 6 MHz Operation ■ 600 mA maximum load capability ■ 6 MHz PWM fixed switching frequency (typ.) ■ 27 µA (typ.) quiescent current in PFM mode ■ Wide Input Voltage Range: 2.3V to 5.5V ■ ±1.5% DC output voltage precision over temperature ■ Best-in-class load transient response ■ Low output ripple in PFM mode ■ Automatic PFM/PWM mode switching ■ Current overload and thermal shutdown protection ■ Internal soft-start ■ Micro SMD 6–bump package (1.065 x 1.265 , 0.6 mm height) ■ Total solution size < 7mm2 (works with 0402 capacitors) ■ UVLO
Applications
■ Mobile Phones ■ MP3 players ■ Wireless LAN ■ PDAs, Pocket PCs ■ Portable Hard Disk Drives Typical Application Circuit 30082230 Efficiency vs. Output Current (Auto Mode, VOUT = 1.82V) 30082201 © 2009 National Semiconductor Corporation 300822 www.national.com LM8801 High Precision 6MHz, 600 mA Synchronous Step-Down DC-DC Converter for Mobile
FIGURE 1. 6-Bump micro SMD Package date code; “V” is an NSC internal code for die traceability. Both will vary in production. A1 Mode Auto mode and forced PWM model selection. Forced PWM = HIGH; Auto = LOW. A2 VIN Power supply input. Connect to the input filter capacitor (Typical Application Circuit, page 1). B1 SW Switching node connection to the internal PFET switch and NFET synchronous rectifier. when > 1.2V. Do not leave this pin floating.
Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN Pin to GND −0.2V to 6.0V EN, MODE pin to GND −0.2V to 6.0V FB, SW pin (GND−0.2V) to (VIN + 0.2V) w/ 6.0V max Junction Temperature (TJ-MAX) +150°C Storage Temperature Range −65°C to +150°C Continuous Power Dissipation (Note 3) Internally Limited Maximum Lead Temperature (Soldering, 10 sec.) 260°C ESD Rating (Note 4) Human Body Model 2 kV Machine Model 200V Operating Ratings (Notes 1, 2) Input Voltage Range 2.3V to 5.5V Recommended Load Current 0 mA to 600 mA Junction Temperature (TJ) Range −30°C to +125°C Ambient Temperature (TA) Range (Note 5) −30°C to +85°C Thermal Properties Junction-to-Ambient Thermal Resistance (θJA) (Micro SMD) (Note 6) 85°C/W Electrical Characteristics (Notes 2, 7, 8) Limits in standard typeface are for TA = 25°C. Limits in boldface type apply over the operating ambient temperature range (−30°C ≤ TA = TJ ≤ +85°C). Unless otherwise noted, specifications apply to the LM8801 open loop Typical Application Circuit with VIN = EN = 3.6V. Symbol Parameter Condition Min Typ Max Units VFB Feedback Voltage Tolerance PWM -1.5 +1.5 % VOUT Line Reg. (closed loop) 2.3V ≤ VIN ≤ 5.5V; IOUT = 10 mA (PFM) 0.2 %/V 2.3V ≤ VIN ≤ 5.5V; IOUT = 200 mA (PWM) 0.048 Load Reg. (closed loop) 0.1 mA ≤ IOUT ≤ 600 mA; VIN = 3.6V (Auto) 0.0019 %/mA ISHDN Shutdown Supply Current EN = 0V, SW = GND 0.08 1.0 µA IQ_PFM Quiescent Current in PFM Mode No load, device is not switching 27 35 µA IQ_PWM Quiescent Current in PWM Mode No load, device is not switching 0.57 0.7 mA RDSON (P) Pin-Pin Resistance for PFET VIN = VGS = 3.6V 220 mΩ RDSON (N) Pin-Pin Resistance for Sync NFET VIN = VGS = 3.6V 180 mΩ ILIM PFET Peak Current Limit 900 1100 1300 mA VIH Logic High Input, all control pins 1.2 V VIL Logic Low Input 0.4 V IEN,MODE Pin Input Current 0.01 1 µA FOSC Internal Oscillator Frequency PWM Mode 5.6 6.0 6.4 MHz UVLO Under-Voltage Lock Out 2.0 V 3 www.national.com LM8801
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ = 140°C (typ.). Note 4: The Human Body Model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. MIL-STD-883–3015.7. Note 5: In applications where high power dissipation and/or poor package resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125°C), the maximum power dissipation of the device in the application (PD-MAX) and the junction-to-ambient thermal resistance of the part/package (θJA) in the application, as given by the following equation: TA-MAX = TJ-MAX− (θJAx PD-MAX). Due to the pulsed nature of testing the part, the temp in the Electrical Characteristic table is specified as TA = TJ. Note 6: Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high power dissipation exists, special care must be given to thermal dissipation issues in board design. Note 7: Min and Max limits are guaranteed by design, test or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 8: The parameters in the electrical characteristic table are tested under open loop conditions at VIN = 3.6V unless otherwise specified. For performance over the input voltage range and closed loop condition, refer to the datasheet curves. www.national.com 4 LM8801
FIGURE 2. Simplified Functional Diagram
Typical Performance Characteristics LM8801TL-1.82, Typical Application Circuit (page 1), VOUT = 0.5 µH, 2012 (MIPSZ2012D0R5), unless otherwise noted. Efficiency vs. Output Current (Auto Mode) 30082202 Efficiency vs. Output Current (PWM Mode) 30082203 Efficiency vs. Output Current (PWM Mode) 30082212 Output Voltage vs. Output Current (Auto Mode) 30082204 Output Voltage vs. Supply Voltage (PWM) 30082207 PFM ↔ PWM Mode Change Point 30082211 www.national.com 6 LM8801
Typical Switching Waveform (PWM Mode, IOUT = 300 mA) 30082210 Typical Switching Waveform (PFM Mode IOUT = 50 mA) 30082208 Load Transient Response (0 ↔ 150 mA) 30082235 Load Transient Response (50 ↔ 350 mA) 30082236 Load Transient Response (150 ↔ 400 mA) 30082237 Load Transient Response (250 ↔ 600 mA) 30082238 7 www.national.com LM8801
(3.0 VIN ↔ 3.6 VIN, 250 mA) 30082239 Startup in PFM Mode (IOUT = 20 mA) 30082240 Startup in PWM Mode (IOUT = 300 mA) 30082241 www.national.com 8 LM8801
external power components are required for implementation. switch on time to control the average current sent to the load. erage voltage at the SW pin. the converter to achieve excellent load and line regulation. proportional to the input voltage is introduced. by the clock turning off the NFET and turning on the PFET. drop during a load transient from light to heavy load. FIGURE 3. Operation in PFM Mode and Transfer to PWM Mode
INTERNAL SYNCHRONOUS RECTIFICATION While in PWM mode, the LM8801 uses an internal NFET as a synchronous rectifier to reduce rectifier forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in efficiency whenever the output voltage is relatively low compared to the voltage drop across an ordinary rectifier diode. CURRENT LIMITING A current limit feature allows the LM8801 to protect itself and external components during overload conditions. PWM mode implements current limit using an internal comparator that trips at 1.1A (typ). If the output is shorted to ground the device enters a timed current limit mode where the NFET is turned on for a longer duration until the inductor current falls below a low threshold, ensuring inductor current has more time to decay, thereby preventing runaway. SHUTDOWN MODE Setting the EN input pin low (<0.4V) places the LM8801 in shutdown mode. During shutdown the PFET switch, NFET switch, reference, control and bias circuitry of the LM8801 are turned off. Setting EN high (>1.2V) enables normal operation. While turning on the device with EN soft-start is activated. EN pin should be set low to turn off the LM8801 during system power up and under-voltage conditions when the supply is less than 2.3V. Do not leave the EN pin floating. SOFT-START The LM8801 has a soft-start circuit that limits in-rush current during start-up. During start-up the switch current limit is in- creased in steps. Soft start is activated only if EN goes from logic low to logic high after VIN reaches 2.3V. THERMAL SHUTDOWN PROTECTION The LM8801 has a thermal overload protection function that operates to protect itself from short-term misuse and overload conditions. When the junction temperature exceeds around 150°C, the device inhibits operation. Both the PFET and the NFET are turned off. When the temperature drops below 130°C, normal operation resumes. Prolonged operation in thermal overload conditions may damage the device and is considered bad practice. UVLO (UNDER-VOLTAGE LOCK OUT) The LM8801 has an UVP comparator to turn the power device off in the case the input voltage or battery voltage is too low. The typical UVP threshold is around 2V with 100 mV hystere- sis. www.national.com 10 LM8801
Application Information
There are two main considerations when choosing an induc- tor; the inductor should not saturate, and the inductor current ripple is small enough to achieve the desired output voltage ripple. Different manufacturers follow different saturation cur- rent rating specifications, so attention must be given to de- tails. Saturation current ratings are typically specified at 25°C so ratings at maximum ambient temperature of application should be requested from manufacturer. Minimum value of inductance to guarantee good perfor- mance is 0.3 µH at (ILIM typ.) bias current over the ambient temp range. Shielded inductors radiate less noise and should be pre- ferred. There are two methods to choose the inductor satu- ration current rating. Method 1: The saturation current should be greater than the sum of the maximum load current and the worst case average to peak inductor current. This can be written as:
- IRIPPLE: average to peak inductor current
- IOUTMAX: maximum load current (600 mA)
- VIN: maximum input voltage in application
- L: minimum inductor value including worst case tolerances (30% drop can be considered for method 1)
- f: minimum switching frequency (5.4 MHz)
- VOUT: output voltage Method 2: A more conservative and recommended approach is to choose an inductor that can handle the maximum current limit of 1300 mA. The inductor's resistance should be less than around 0.1Ω for good efficiency. Table 1 lists suggested inductors and sup- pliers. INPUT CAPACITOR SELECTION A ceramic input capacitor of 2.2 µF, 6.3V is sufficient for most applications. Place the input capacitor as close as possible to the VIN pin of the device. A larger value or higher voltage rat- ing may be used to improve input voltage filtering. Use X7R or X5R types; do not use Y5V. DC bias characteristics of ce- ramic capacitors must be considered when selecting case sizes like 0402 and 0603. The input filter capacitor supplies current to the top switch of the LM8801 in the first half of each cycle and reduces voltage ripple imposed on the input power source. A ceramic capacitor's low ESR provides the best noise filtering of the input voltage spikes due to this rapidly changing current. Se- lect an input filter capacitor with sufficient ripple current rating. The input current ripple can be calculated as: The worst case is when VIN = 2 x VOUT.
TABLE 1. Suggested Inductors and Suppliers
- DC bias characteristics vary from manufacturer to man-
pacitance and sufficiently low ESR to perform these functions. culations is at the switching frequency of the part. Table 2 lists suggested capacitors and suppliers.
TABLE 2. Suggested Capacitors and Suppliers detailed in National Semiconductor Application Note 1112. specific instructions how to do this. joints can result in erratic or degraded performance. a few simple design rules, as illustrated in Figure 4. FIGURE 4. LM8801 Board Layout (Top View)
- Place the LM8801 on 8.26 mil pads. As a thermal relief,
Micro SMD Package Assembly and Use).
- Place the LM8801, inductor and filter capacitors close
input filter capacitor very close to the VIN and GND pin.
- Arrange the components so that the switching current
- Connect the ground pins of the LM8801, and filter
impedance ground connection.
- Use wide traces between the power components and for power connections to the DC-DC converter circuit. This reduces voltage errors caused by resistive losses across the traces. 6. Route noise sensitive traces such as the voltage feedback path away from noisy traces between the power components. The voltage feedback trace must remain close to the LM8801 circuit and should be routed directly from FB to VOUT at the output capacitor and should be routed opposite to noise components. This reduces EMI radiated onto the DC-DC converter’s own voltage feedback trace. 7. Place noise sensitive circuitry, such as radio IF blocks, away from the DC-DC converter, CMOS digital blocks and other noisy circuitry. Interference with noise- sensitive circuitry in the system can be reduced through distance. In mobile phones, for example, a common practice is to place the DC-DC converter on one corner of the board, arrange the CMOS digital circuitry around it (since this also generates noise), and then place sensitive preamplifiers and IF stages on the diagonally opposing corner. Often, the sensitive cir- cuitry is shielded with a metal pan and power to it is post- regulated to reduce conducted noise, using low-dropout linear regulators. 13 www.national.com LM8801
Physical Dimensions inches (millimeters) unless otherwise noted 6–bump (Large) micro SMD, 0.4 mm pitch X1 = 1.065 mm ± 0.030 mm X2 = 1.265 mm ± 0.030 mm X3 = 0.6 mm ± 0.075 mm * Pin A1 is established by lower left corner with respect to text orientation www.national.com 14 LM8801
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