EC3210 E-CMOS | Alldatasheet
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Technical content
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout GENERAL DESCRIPTION
FEATURES
The EC3210 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. The device is available in an adjustable version. Supply current during operation is only 20mA and drops to ≤1mA in shutdown. The 2.5V to 5.5V input voltage range makes the EC3210 ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. Automatic Burst Mode operation increases efficiency at light loads, further extending battery life. Switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors and capacitors. The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. The EC3210 is available in a low profile (1mm) TSOT23-5 package.
Applications
- Cellular Telephones
- Personal Information Appliances
- Wireless and DSL Modems
- Digital Still Cameras
- MP3 Players
- Portable Instruments Package Type TSOT23-5
Figure 1. Package Types of EC3210
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Pin Assignment Pin Name Description 1 RUN Run Control Input. Forcing this pin above 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. In shutdown, all functions are disabled drawing <1uA supply current. Do not leave RUN floating. 2 GND Ground Pin.
3 SW Switch Node Connection to
Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. 4 VIN Main Supply Pin. Must be closely decoupled to GND, Pin 2, with a 2.2uF or greater ceramic capacitor. 5 VFB Feedback Pin. Receives the feedback voltage from an external resistive divider across the output. 5 VOUT Output Voltage Feedback Pin. An internal resistive divider divides the output voltage down for comparison to the internal reference voltage.
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout
Ordering Information
Part Number Package Marking Marking Information EC3210ADJT2R TSOT23-5 10AJf 1. Starting with underlined 0, a bar is for production year 2012. The next bar is mark on top of A is for year 2013. The next bar is mark on bottom of A is for year 2014. The next bar is mark on top of J is year for 2015. The naming pattern continues with consecutive characters for later years. 2. AJ：Adjustable Voltage 3. f is the week of production. The big character of A~Z is for the week of 1~26, and small a~z is for the week of 27~52. Functional Block Diagram Figure 2. Function Block Diagram of EC3210
Figure 3. Type Application Circuit of EC3210 maximum rating conditions for extended periods may affect reliability.
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout
ELECTRICAL CHARACTERISTICS
(VIN=3.6V,TA=25°C, Unless otherwise specified) Parameter Symbol Conditions Min Typ Max Unit Feedback current INFB --- --- 30 nA Regulator Feedback Voltage VFB TA=25℃ 0.5880 0.6000 0.6120 V 0℃≦TA≦85℃ 0.5865 0.6000 0.6135 V -40℃≦TA≦85℃ 0.585 0.6000 0.6150 V Reference Voltage Line Regulator VFB VIN=2.5V to 5.5V --- 0.04 0.4 %/V Peak Inductor Current IPK VIN=3V,VFB=0.5V or Vout=90%,Duty Cycles <35% 1.05 1.10 1.15 A Input Voltage Range VIN 2.5 5.5 V Input DC Bias Current Active Mode IS VFB=0.5V or Vout=90%, ILoad=0A --- 300 400 uA Sleep Mode VFB=0.62V or Vout=103%, ILOAD=0A --- 45 70 uA Shut down VRUN=0V,VIN=4.2V --- 0.1 1 uA Oscillator Frequency fOSC VFB=0.6V or Vout=100% 1 1.5 2 MHz VFB=0V or Vout=0V --- 400 --- KHz RDS(ON) of P-Channel FET RPFET ISW=100mA --- 0.35 0.45 Ω RDS(ON) of N-Channel FET RNFET ISW=-100mA --- 0.35 0.45 Ω SW Leakage ILSW VRUN=0V,VSW=0V or 5V, VIN=5V --- 0.01 1 uA RUN Threshold VRUN 0.3 1 1.5 V RUN Leakage Current IRUN 0.01 1 uA
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Typical Performance Characteristics
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Typical Performance Characteristics(Cont.)
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Typical Performance Characteristics(Cont.)
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Typical Performance Characteristics(Cont.)
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Function Description the EA amplifier’s output rises above the sleep threshold Main Control Loop The EC3210 uses a constant frequency, current mode step-down architecture. Both the main (P-channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator, ICOMP , resets the RS latch. The peak inductor current at which ICOMP resets the RS latch, is controlled by the output of error amplifier EA. When the load current increases, it causes a slight decrease in the feedback voltage, FB, relative to the 0.6V reference, which in turn,causes the EA amplifier’s output voltage to increase until the average inductor current matches the new load current. While the top MOSFET is off, the bottom MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current reversalcomparator IRCMP, or the beginning of the next clock cycle. Burst Mode Operation The EC3210 is capable of Burst Mode operation in which the internal power MOSFETs operate intermittently based on load demand. In Burst Mode operation, the peak current of the inductor is set to approximately 200mA regardless of the output load. Each burst event can last from a few cycles at light loads to almost continuously cycling with short sleep intervals at moderate loads. In between these burst events, the power MOSFETs and any unneeded circuitry are turned off, reducing the quiescent current to 30uA. In this sleep state, the load current is being supplied solely from the output capacitor. As the output voltage droops, signaling the BURST comparator to trip and turn the top MOSFET on. This process repeats at a rate that is dependent on the load demand. ShortCircuit Protection When the output is shorted to ground, the frequency of the oscillator is reduced to about 400kHz, 1/4 the nominal frequency. This frequency foldback ensures that the inductor current has more time to decay, thereby preventing runaway. The oscillator’s frequency will progressively increase to 1.5MHz when VFB or VOUT rises above 0V. Dropout Operation As the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor. An important detail to remember is that at low input supply voltages, the RDS(ON) of the P-channel switch increases (see Typical Performance Characteristics). Therefore, the user should calculate the power dissipation when the EC3210 is used at 100% duty cycle with low input voltage (See Thermal Considerations in the Applications Information section).
voltage for various output voltages.
- External component selection is driven by the load
values will cause the burst frequency to increase. Figure 4. Maximum Output Current vs Input Voltag e
size/current and price/current relationship of an inductor. inductors that work well in EC3210 applications. Table 1. Representative Surface Mount Inductors the manufacturer if there is any question. low ESR so they give the lowest ESR for a given volume.
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Function Description(Cont.) RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC) The RDS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Charateristics curves. Thus, to obtain I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. Other losses including CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss. Thermal Considerations In most applications the EC3210 does not dissipate much heat due to its high efficiency. But, in applications Figure 6:Power Lost VS Load Current where the EC3210 is running at high ambient 1. The VIN quiescent current is due to two components: temperature with low supply voltage and high duty the DC bias current as given in the electrical cycles, such as in dropout, the heat dissipated may characteristics and the internal main switch and exceed the maximum junction temperature of the part. If synchronous switch gate charge currents. The gate the junction temperature reaches approximately 150°C, charge current results from switching the gate both power switches will be turned off and the SW node capacitance of the internal power MOSFET switches. will become high impedance. Each time the gate is switched from high to low to high To avoid the EC3210 from exceeding the maximum again, a packet of charge, dQ, moves from VIN to junction temperature, the user will need to do some ground. The resulting dQ/dt is the current out of VIN that thermal analysis. The goal of the thermal analysis is to is typically larger than determine whether the power dissipated exceeds the the DC bias current. In continuous mode, IGATECHG maximum junction temperature of the part. The =f(QT + QB) where QT and QB are the gate charges of temperature rise is given by: the internal top and bottom switches. Both the DC bias TR = (PD)(qJA) and gate charge losses are proportional to VIN and where PD is the power dissipated by the regulator and thustheir effects will be more pronounced at higher qJA is the thermal resistance from the junction of the die supply voltages. to the ambient temperature. 2. I2R losses are calculated from the resistances of the The junction temperature, TJ, is given by: internal switches, RSW, and external inductor RL. In TJ = TA + TR continuous mode, the average output current flowing where TA is the ambient temperature. through inductor L is “chopped” between the main switch As an example, consider the EC3210 in dropout at an and the synchronous switch. Thus, the series resistance input voltage of 2.7V, a load current of 800mA and an looking into the SW pin is a function of both top and ambient temperature of 70°C. From the typical bottom MOSFET RDS(ON) and the duty cycle (DC) as performance graph of switch resistance, the RDS(ON) of follows: the P-channel switch at 70°C is approximately 0.52W.
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout Function Description(Cont.) Therefore, power dissipated by the part is: PD = ILOAD 2 • RDS(ON) = 187.2mW For the SOT-23 package, the qJA is 250°C/ W. Thus, the junction temperature of the regulator is: which is below the maximum junction temperature of 125°C. Note that at higher supply voltages, the junction temperature is lower due to reduced switch resistance (RDS(ON)). Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to (ΔILOAD • ESR), where ESR is the effective series resistance of COUT. ΔILOAD also begins to charge or discharge COUT, which generates a feedback error signal. The regulator loop then acts to return VOUT to its steadystate value. During this recovery time VOUT can be monitored for overshoot or ringing that would indicate a stability problem. For a detailed explanation of switching control loop theory, see Application Note 76. A second, more severe transient is caused by switching in loads with large (>1μF) supply bypass capacitors. The discharged bypass capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem if the load switch resistance is low and it is driven quickly. The only solution is to limit the rise time of the switch drive so that the load rise time is limited to approximately (25 • CLOAD).Thus, a 10μF capacitor charging to 3.3V would require a 250μs rise time, limiting the charging current to about 130mA.
EC3210 1.5MHz, 800mA, Synchronous Step-Down Regulator Dropout
Package Information
TSOT235 Package Outline Dimensions