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| 4.85 VOLT ULTRA LOW DROPOUT REGULATOR ISSUE 2 - MAY 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 2.7 to 18 volts, this device provides an output voltage of 4.85 volts. The ZLDO485 consumes a typical quiescent current of only 1mA and is rated to supply load currents up to 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 ZLDO485 FEATURES * * * * * * * * * * * * * * * * Very low dropout voltage 6mV dropout at 10mA output 30mV dropout at 100mA output 100mV dropout at 300mA output 4.85 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 4-71 ZLDO485 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 SYMBOL Vo CONDITIONS Vin=5.85V Vin=5.85V (Note 2, Note 4) Vin=5.85 to 20V IL=10 to 300mA Vin=5.85V IL=10mA IL=100mA IL=300mA Vin=5.85V, IL=0 Vin=5.85V, IL=0, Vshdn=Vin Vshdn=Vin=5.85V Vin=5.85V low(on) high(off) Vin=20V Vo=Gnd Vin=5.85V f=10Hz to100kHz, IL=100mA Vo + 0.2V Ibl=100A, Vin Vo Output voltage temperature coefficient T Line regulation Load regulation Dropout voltage (Note3) Quiescent current Quiescent current at shutdown 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) Vts 0.4 1.5 50 100 V nA ILs en 190 V RMS Low battery detect voltage Low battery flag output voltage Low battery flag leakage current Vin(bld) Vbl Ibl Vo + 0.4V 0.4 1 V V A ZLDO485 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 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. 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. 4-73 ZLDO485 TYPICAL CHARACTERISTICS 1800 C(out)= 1F 1600 45 40 1400 1200 1000 800 600 400 200 5 0 100 1K 10K 100K 100 1K 10K 100K 10pF 4.7pF 2.2pF C(out)= 1F Output Impedance (m ) Ripple Rejection (dB) 35 30 25 20 15 10 10pF 4.7pF 2.2pF Frequency (Hz) Frequency (Hz) Output Impedance vs. Frequency Ripple Rejection vs. Frequency 4.89 4.88 Io= 10mA V(in)= 7V 720 V(in)= 7V 700 Quiescent Current (A) Output Voltage (V) 680 660 640 620 600 580 560 540 -40 4.87 4.86 4.85 4.84 4.83 4.82 -40 -20 0 20 40 60 80 100 -20 0 20 40 60 80 100 Temperature ( C) Temperature ( C) Output Voltage Temperature Coefficient Quiescent Current vs. Temperature 18 V(in)= 7V 5.15 V(in)= 7V Io= 10mA L.B.F. Operation Voltage (V) -20 0 20 40 60 80 100 Shutdown Current (A) 16 5.14 14 5.13 12 5.12 10 5.11 8 5.10 6 -40 5.09 -40 -20 0 20 40 60 80 100 Temperature ( C) Temperature ( C) Shutdown Current vs. Temperature Low Battery Flag Operating Point 4-74 ZLDO485 TYPICAL CHARACTERISTICS 220 V(in)=7V 200 Output Voltage Deviation (V) Io=100mA V(in)=12V Dropout Voltage (mV) 180 160 140 120 100 80 60 40 20 0 0.1 1.0 10 100 1000 85 C 25 C -40 C V(in)=7V 1 Output Voltage Deviation 0 -1 0 200 400 600 800 1000 Load Current (mA) Time (s) Dropout Voltage vs. Load Current Line Transient Response SINGLE PULSE TEST Tamb =25 C 1.0 Output Voltage Deviation (V) V(in)=7V Io=100mA DC 1s 0.1s 10ms Io=0mA Load Current (A) DC 0.1 0.5 Output Voltage Deviation 0 -0.5 0.01 0 200 400 600 800 1000 1 2 5 10 20 Time (s) Input-Output Differential Voltage (V) Load Transient Response Safe Operating Area Operation in shaded area is not guaranteed 4-75 ZLDO485 APPLICATIONS 1). Operation From A Low Voltage Battery Pack Fig.1 shows the ZLDO485 regulator being used to stabilise the output of a 6V battery pack. The ultra low dropout voltage of only 100mV at full load (300mA) given by the regulator allows the minimum number of cells to be used in the pack and also maximises the energy that can be removed from the battery before the output of the regulator starts to fail. ZLDO485 LBF Spg SC Vin Gnd D/C currents, sometimes approaching as much as a tenth of their maximum load current specification when approaching dropout conditions. Despite its 300mA output rating, when enabled the ZLDO485 consumes typically only 630uA regulating normally and 3mA when the input falls too low for regulation. 2). Post Converter Regulation 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 change 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 C1 10pF + 4.85V N/C Vout 6V C3 100nF C2 1uF Output 0V Figure 1 At a load current of 100mA the dropout voltage falls to around 30mV. The endurance of the battery pack is not only dependent on dropout voltage. When operating, some low dropout regulators can consume high quiescent Voltage Feedback D1 +12V Out TR1 D2 C4 220uF ZLDO485 LBF Spg SC Vin Gnd D/C Switching Regulator C1 10pF +4.85V Out N/C Vout 220uF C5 C2 1uF Figure 2 0V Out 4-76 ZLDO485 APPLICATIONS output impedance of the switching power supply but no higher. The low dropout voltage of the ZLDO485 allows this circuit technique to be implemented very effectively, giving a highly stable and accurate low noise supply. 4). Over Temperature Shutdown The ZLDO485 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. 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 3). Logic Controlled Power Supply Fig.3 shows all that is necessary to allow a microprocessor to control a power supply based on the ZLDO485 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 + 6.7V to 20V IC1 ZSR500 Vin Vout Gnd Microproc. System IC2 ZLDO485 LBF Spg SC Vin Gnd D/C C1 10pF + 4.85V Supply Input N/C Vout C3 100nF C2 1uF Switched Output 0V 0V Figure 3 is shutdown in this way, the quiescent current of the ZLDO485 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). 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 ZLDO485 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 b o u nd a r i e s I nd i ca te d i n t he t yp i cal characteristics. 4-77 ZLDO485 APPLICATIONS 5). Low Battery Flag The ZLDO485 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 ZLDO485 series indicates that the voltage drop across the regulator has fallen to less than typically 300mV and so supply failure is imminent. This improved warning gives both more time for the system suppl ied 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. Fig.4 shows this output being used. Note that resistor R1 is necessary only if the interrupt logic does not include a pull-up resistor. ZLDO485 LBF Spg SC Vin Gnd D/C C1 10pF + 4.85V R1 100k Microproc. System Interrupt Input N/C Vout 6V C3 100nF C2 1uF Figure 4 0V 4-78 ZLDO485 CONNECTION DIAGRAM SM8 Package Suffix - T8 Top View - Pin 6 must be left floating SEE PIN DEFINITIONS ORDERING INFORMATION Part Number ZLDO485T8 Package SM8 Part Mark ZLDO485 4-79 |
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