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| 2.70 VOLT ULTRA LOW DROPOUT REGULATOR Issue 2 June 1997 DEVICE DESCRIPTION The ZLDO Series low dropout linear regulators operate with an exceptionally low dropout voltage, typically only 30mV with a load current of 100mA. The regulator series features output voltages in the range 2.70 to 12 volts, this device provides an output voltage of 2.70 volts. The ZLDO270 consumes a typical quiescent current of only 1mA at its maximum rated output current of 300mA. A battery low flag is available to indicate potential power fail situations. If the input voltage falls to within 200mV of the regulated output voltage then the error output pulls low. The device also features an active high disable control. Once disabled the ZLDO quiescent current falls to typically 11A. The ZLDO devices are packaged in Zetex SM8 8 pin small outline surface mount package, ideal for applications where space saving is important. The device low dropout voltage, low quiescent current and small size make it ideal for low power and battery powered applications. Battery powered circuits can make particular use of the low battery flag and shutdown features. Low Battery Flag ZLDO270 FEATURES * * * * * * * * * * * * * * * * Very low dropout voltage 6mV dropout at 10mA output 30mV dropout at 100mA output 100mV dropout at 300mA output 2.70 volt fixed output Other voltages available Low quiescent current 1mA quiescent (typ) at 300mA output Low battery flag Shutdown control Surface mount package APPLICATIONS Battery powered devices Portable instruments Portable communications Laptop/Palmtop computers Electronic organisers Vin LOW BATTERY COMPARATOR THERMAL SHUTDOWN Vo Shutdown Control SHUTDOWN BIAS CIRCUIT OUTPUT DRIVE Cs BANDGAP REFERENCE Shaping Gnd ZLDO270 ABSOLUTE MAXIMUM RATING Input Supply Voltage Range Shutdown Input Voltage Range Low Battery Output Voltage Range -0.3 to 20V -0.3 to Vin -0.3 to 20V Output Current Operating Temperature Storage Temperature Power Dissipation (Tamb=25C) 300mA -40 to 85C -55 to 150C 2W (Note 1) ELECTRICAL CHARACTERISTICS TEST CONDITIONS (Unless otherwise stated) Tamb =25C,IL=10mA,Cs=10pF,Cout =1F Parameter Output voltage Output voltage temperature coefficient Line regulation Load regulation Dropout voltage (Note3) Quiescent current Quiescent current at shutdown SYMBOL Vo Vo T CONDITIONS Vin=3.7V Vin=3.7V (Note 2, Note 4) Vin=3.7 to 20V IL=10 to 300mA Vin=3.7V IL=10mA IL=100mA IL=300mA Vin=3.7V, IL=0 Vin=3.7V, IL=0, Vshdn=Vin Vshdn=Vin=3.7V Vin=3.7V low(on) high(off) Vin=20V Vo=Gnd Vin=3.7V f=10Hz to 100kHz, IL=100mA VO + 0.2 Ibl=100A, Vin Vo Vo Vin-Vo Iq Iqs mA A A Shutdown control input Iins current Shutdown control threshold voltage Output current in shutdown mode (Note4) Output noise voltage (Note4) Low battery detect voltage Low battery flag output voltage Low battery flag leakage current Vts 0.4 1.5 50 100 V nA ILs en 140 V RMS Vin(bld) Vbl Ibl VO + 0.4 V 0.4 1 V A ZLDO270 NOTES. 1. Maximum power dissipation of the device is calculated assuming the package is mounted on a PCB measuring 2 inches square. 2 Output voltage temperature coefficient is calculated as:- VO change x 1000000 VO x temperature change 3. Dropout voltage is defined as the input to output voltage differential at which the circuit ceases to regulate. The value is measured when the output voltage has dropped by 100mV from V out measured at the nominal input Vin = Vout + 1V 4. Guaranteed by design. FUNCTIONAL DESCRIPTION The ZLDO is a high performance, ultra low dropout, low quiescent regulator. Available in SM8 surface mount packaging, the device is able to dissipate 2W(note 1) allowing complete design flexibility with an input span upto 20V and 300mA output current. The device quiescent is 1mA (typ) at 300mA load current. A low battery comparator signifies impending battery failure, whilst a shutdown function reduces quiescent current to a mere 11A (typ). A precision bandgap reference gives 2.5% output tolerance and good temperature characteristics over the range -40 to +85C. AC performance is enhanced via the use of a small external capacitor. PIN DEFINITIONS Pin 1 LBF - Low Battery Flag. An open collector NPN output which pulls low on failing input supply. Pin 2 SC - Shutdown Control. This high impedance logic compatible input disables the regulator when taken high. It includes a diode wired to Vin and so will pass current if taken more than 0.5V above Vin. Pin 3 Vin - Voltage Input. The power supply to the regulator. The permissible input voltage range is -0.3 to 20V. An input capacitor is not mandatory but will be useful in reducing the coupling of noise from input to output and minimising the effect of sudden changes in load current on the input voltage. Pin 4 N/C - Not Connected. Not internally connected and so can be left open or wired to any pin without affecting the performance of the regulator. Pin 5 Vout - Voltage Output. The output of the regulator. An output capacitor of 1uF or greater and having low ESR should be wired in close proximity to the regulator to ensure stability for all loads. Pin 6 D/C - Do Not Connect. This pin is wired to an internal circuit node of the regulator. No external connection should be made to this pin. Pin 7 Gnd - Ground. The ground connection of the regulator against which the output voltage is referenced. Pin 8 Spg - Shaping. The shaping node for the error amplifier of the regulator. A capacitor of 10pF wired from this pin to the output pin (pin 5) gives optimum stability. Improved AC can be achieved by reducing the value of this capacitor but stability may be impaired for some load conditions. ZLDO270 TYPICAL CHARACTERISTICS 1000 Cout = 1uF 55 50 Cout=1F Output Impedance (m ) 800 Ripple Rejection (dB) 45 40 35 30 25 20 15 10 5 0 100 2.2pF 4.7pF 10pF 600 400 200 0 100 10pF 4.7pF 2.2pF 1k 10k 100k 1k 10k 100k Frequency (Hz) Frequency (Hz) Output Impedance v Frequency Ripple Rejection v Frequency 2.730 2.725 Io=10mA Vin=5v 600 Vin=5v Quiescent Current (A) 0 20 40 60 560 520 480 440 400 -40 Output Voltage (V) 2.720 2.715 2.700 2.695 2.690 -40 -20 80 -20 0 20 40 60 80 Temperature (C) Temperature (C) Output Voltage Temperature Coefficient Quiescent Current v Temperature 16.0 Vin=5v 3.00 Vin=5v Io=10mA L.B.F. Operation Voltage (V) Shutdown Current (uA) 14.0 12.0 2.99 2.98 2.97 2.96 2.95 2.94 2.93 -40 10.0 8.0 6.0 -40 -20 0 20 40 60 80 -20 0 20 40 60 80 Temperature ( C) Temperature (C) Shutdown Current v Temperature Low Battery Flag Operating Point ZLDO270 TYPICAL CHARACTERISTICS 200 180 Vin=10v Dropout Voltage (mV) 160 140 120 100 80 60 40 20 0 0.1 1 10 100 1000 85C 25C -40C Output Voltage Deviation (V) Vin=5v 0.8 0.4 0 -0.4 0 200 400 600 800 1000 Io=100mA Output Voltage Deviation Load Current (mA) Time (s) Dropout Voltage v Load Current Line Transient Response Vin=5v 1.0 Io=100mA DC 1s 0.1s 10ms Output Voltage Deviation (V) 0.4 0 Output Voltage Deviation Load Current (A) 160 200 Io=0mA 0.1 -0.2 -0.4 0 40 80 120 0.01 1 2 5 10 20 Time (s) Input-Output Differential Voltage (V) Load Transient Response Safe Operating Area Operation in shaded area not guaranteed ZLDO270 APPLICATIONS 1). Simple 2.70V Supply +5V In IC1 ZLDO270 LBF Spg SC Vin Gnd D/C 2). Post Converter Regulation +5V Out C1 10pF +2.70V Out N/C Vout C3 100nF C2 1F 0V In 0V Out Figure 1 Using a circuit such as Figure 1, the ZLDO270 can easily provide a 2.70V logic supply from an available 5V rail where most standard regulators could not guarantee correct operation. Although this approach is not particularly energy efficient, if the load taken at 2.70V is not too large, then the added complexity and cost of a 2.70V switching converter may not be justifiable and so this linear solution can be preferable. This circuit will also give far less noise than a switching regulator which can be important when handling low level analogue signals or low voltage measurements. Voltage Feedback D1 A common problem with multiple output switch mode converters is that only one output can be used in the feedback control loop of the switching regulator. Thus only one output is fully regulated. All other outputs are prone to tracking errors that occur if the load on any output changes significantly. By ensuring close coupling of all transformer windings and minimising the impedance of all outputs, these errors can be reduced but never eliminated. A simple way round this problem is to wind the switching regulator transformer to give a slightly higher voltage than required and regulate down from this to the desired voltage with a linear regulator. This is indicated in Figure 2. To keep losses low and so maintain the advantages of a switch mode supply, it is important that the voltage drop across this regulator is kept as low as possible, i.e. just high enough to compensate for the poor output impedance of the switching power supply but no higher. The low dropout voltage of the ZLDO270 allows this circuit technique to be implemented very effectively, giving a highly stable and accurate low noise supply. +5V Out TR1 D2 C4 220F ZLDO270 LBF Spg SC Gnd Vin D/C N/C Vout Switching Regulator C1 10pF +2.70V Out 220F C5 C2 1F Figure 2 0V Out ZLDO270 APPLICATIONS 3). Low Battery Flag The ZLDO270 provides an output called Low Battery Flag (LBF). Unlike many regulators that only signal that they are falling out of regulation, the LBF output of the ZLDO270 indicates that the voltage drop across the regulator has fallen to less than typically 200mV and so supply failure is imminent. 4). Over Temperature Shutdown The ZLDO270 regulator includes an over temperature shutdown circuit that disables the regulator if its chip temperature should exceed 125C for any reason. Although intended to provide a limited guard against excessive internal power dissipation, this circuit will shut down the regulator if its ambient rises above 125C. ZLDO270 LBF Spg SC Gnd Vin D/C N/C Vout C1 10pF +2.70V R1 100k Microproc. System Interrupt Input 4.8V C3 100nF C2 1F Figure 3 This improved warning gives both more time for the system supplied to shutdown gracefully and maintains regulation while this happens. This could be a vital point if measurements are under way and must be completed accurately for instance. The LBF output is driven by an open collector NPN transistor which pulls low when the supply to the regulator is failing. Figure 3 shows this output being used. Note that resistor R1 is necessary only if the interrupt logic does not include a pull-up resistor. 0V Thus, the regulator could be used to disable a circuit in the event of the ambient temperature within which the circuit is mounted becoming too high. Any internal power dissipation caused as a result of supplying load current, will reduce the ambient temperature at which shutdown occurs. Note that to achieve the extremely low dropout voltage and high current performance provided by the ZLDO devices, the parts can be damaged by sustained output shorts or excessive loads when combined with high input supply voltages. To ensure reliable operation, keep loads within the SOA graph boundaries indicated in the typical characteristics. ZLDO270 APPLICATIONS 5). Logic Controlled Power Supply Fig.4 shows all that is necessary to allow a microprocessor to control a power supply based on the ZLDO270. The Shutdown Control pin (pin 2), is a logic compatible input that disables the regulator when a voltage in excess of 1.5V is applied. The current required to drive this input is less than 10A. When the regulator is shutdown in this way, the quiescent current of the ZLDO270 falls to around 11A. This makes the regulator suitable for a wide range of battery powered applications where intermittent operation occurs. The shutdown control pin should not be taken to a voltage higher than Vin if low quiescent supply current is important. The shutdown control is a high impedance input and so if not required, should be wired to the ground pin (pin 7). +5.0V to 20V IC1 ZSR330 Vin Vout Gnd Microproc. System IC2 ZLDO270 LBF Spg SC Gnd Vin D/C C1 10pF +2.70V Supply Input N/C Vout C3 100nF C2 1F Switched Output 0V 0V Figure 4 ZLDO270 Connection Diagram SM8 Package Suffix - T8 Top View - Pin 6 must be left floating SEE PIN DEFINITIONS Ordering Information Part Number ZLDO270T8 Package SM8 Part Mark ZLDO270 |
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