L4918 VOLTAGE REGULATORS PLUS FILTER .. .. .. .. PRELIMINARY DATA FIXED OUTPUT VOLTAGE 8.5V 250mA OUTPUT CURRENT HIGH RIPPLE REJECTION HIGH LOAD REGULATION HIGH LINE REGULATION SHORT CIRCUIT PROTECTION THERMAL SHUT DOWN WITH HYSTERESIS DUMP PROTECTION DESCRIPTION The L4918 combines both a filter and a voltage regulator in order to provide a high ripple rejection over a wider input voltage range. A supervisor low-pass loop of the element prevents the output transistor from saturation at low input vol tages. The non linear behaviour of this control circuitry allows a fast setting of the filter. PENTAWATT ORDERING NUMBER : L4918 BLOCK DIAGRAM October 1988 1/6 L4918 PIN CONNECTION (top view) Figure 1 : Application and Test Circuit. ABSOLUTE MAXIMUM RATINGS Symbol Parameter Value Unit Vi Peak Input Voltage (300 ms) 40 V Vi DC Input Voltage 28 V IO Output Current Internally Limited Ptot Power Dissipation Internally Limited Tstg, Tj Storage and Junction Temperature – 40 to 150 °C THERMAL DATA Symbol Parameter Rth j-case Thermal Resistance Junction-case 2/6 Max Value Unit 4 °C/W L4918 ELECTRICAL CHARACTERISTICS (Tamb = 25 °C; Vi = 13.5 V, unless otherwise specified) Symbol Parameter Vi Input Voltage VO Output Voltage Test Conditions Vi = 12 to 18 V IO = 5 to 150 mA Min. Typ. Max. Unit 20 V 8.1 8.5 8.9 V 1.6 2.1 V 1 20 mV 100 mV 150 250 mV 1 2 mA ∆VI/O Controlled Voltage ∆VO Line Regulation Vi = 12 to 18 V IO = 10 mA ∆VO Load Regulation IO = 5 to 250 mA ton = 30 µs toff = ≥ 1 ms ∆VO Load Regulation (filter mode) Vi = 8.5 V IO = 5 to 150 mA ton = 30 µs toff = ≥ 1 ms Iq Quiescent Current IO = 5 mA ∆Iq Quiescent Current Change Vi = 6 to 18 V IO = 5 to 150 mA 0.05 mA ∆VO ∆T Output Voltage Drift IO = 10 mA 1.2 mV/°C SVR Supply Voltage Rejection Viac = 1 Vrms f = 100 Hz IO = 150 mA VIDC = 12 to 18 V VIDC = 6 to 11 V 71 35(*) dB dB 300 mA 500(*) 300 ms ms 150 °C Input-output ISC Short Circuit Current ton Switch On Time TJSD Thermal Shutdown Temperature Dropout Vi = 5 to 10 V IO = 5 to 150 mA 250 IO = 150 mA Vi = 5 to 11 V Vi = 11 to 18 V Junction (*) Depending of the C FT capacitor PRINCIPLE OF OPERATION During normal operation (input voltage upper than VI MIN = VOUT NOM + ∆VI/O). The device works as a normal voltage regulator built around the OP1 of the block diagram. The series pass element use a PNP-NPN connection to reduce the dropout. The reference voltage of the OP1 is derived from a REF throughthe OP2 and Q3, acting as an active zener diode of value VREF. In this condition the device works in the range (1) of the characteristic of the non linear drop control unit (see fig.2). The output voltage is fixed to its nominal value: R1 R1 VOUT NOM = VREF (1 + ) = VCFT (1 + ) R2 R2 R1 = INTERNALLY FIXED RATIO = 2.4 R2 The ripple rejection is quite high (71 dB) and independent from CFT value. On the usual voltage regulators, when the input voltage goes below the nominal value, the regulation transistors (series element) saturate bringing the system out of regulation making it very sensible to every variation of the input voltage. Onthe contrary, a control loop on the L4918 consents to avoid the saturation of the series element by regulating the value of the reference voltage (pin 2). In fact, whenever the input voltagedecreasesbelow VI MIN the supervisor loop, utilizing a non linear OTA, forces the reference voltage at pin 2 to decrease by discharging CFT. So, during the static mode, when the input voltage goes below VMIN the drop out is kept fixed to about 1.6 V. In this condition the device works as a low pass filter in the range (2) of the OTA charac3/6 L4918 teristic. The ripple rejection is externally adjustable acting on CFT as follows: VI (jw) SVR (jw) = = Vout (jw) 10–6 1+ gm R1 (1 + ) R2 jwCFT Where: gm = 2 . 10-5 Ω-1 = OTA’S typical transconductance value on linear region R1 = fixed ratio R2 Figure 2 : Nonliner Transfer Characteristic of the Drop Control Unit. CFT = value of capacitor in µF The reaction time of the supervisor loop is given by the transconductanceof the OTA and by CFT. When the value of the ripple voltageis so high and its negative peak is fast/enough to determine an istantaneous decrease of the dropout till 1.2V, the OTA works in a higher transconductancecondition [range (3) of the characteristic] and discharge the capacitor rapidously. If the ripple frequency is high enough the capacitor won’t charge itself completely, and the output voltage reaches a small value allowing a better ripple rejection; the device’s again working as a filter (fast transient range). With CFT =10 µF ; f = 100 Hz a SVR of 35 is obtained. Figure 3 : Supply Voltage Rejection vs. Fre- 1) Nor mal operati ng range ( high ri ppl e rej ect ion) 2) Drop controlled range (medium rippl e rejection) 3) Fast discharge of C FT Figure 4 : Supply voltage Rejection vs. Input Voltage. 4/6 Figure 5 : Output Voltage vs. Input Voltage. L4918 PENTAWATT PACKAGE MECHANICAL DATA mm DIM. MIN. inch TYP. MAX. A MIN. TYP. 4.8 C MAX. 0.189 1.37 0.054 D 2.4 2.8 0.094 0.110 D1 1.2 1.35 0.047 0.053 E 0.35 0.55 0.014 0.022 F 0.8 1.05 0.031 0.041 F1 1 1.4 G 3.4 G1 6.8 H2 H3 0.039 0.055 0.126 0.134 0.260 0.268 10.4 10.05 0.276 0.409 10.4 0.396 0.409 L 17.85 0.703 L1 15.75 0.620 L2 21.4 0.843 L3 0.142 22.5 0.886 L5 2.6 3 0.102 0.118 L6 15.1 15.8 0.594 0.622 L7 6 6.6 0.236 0.260 M 4.5 M1 4 0.157 3.65 3.85 0.144 0.152 E L D1 C D M A M1 L1 L2 L5 G G1 L3 H3 H2 L7 F Dia. F1 Dia 0.177 L6 5/6 L4918 Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON Microelectronics. 1994 SGS-THOMSON Microelectronics - All Rights Reserved SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A. 6/6