L4915 ADJUSTABLE VOLTAGE REGULATOR PLUS FILTER . .. .. .. . PRELIMINARY DATA OUTPUT VOLTAGE ADJUSTABLE FROM 4 TO 11V HIGH OUTPUT CURRENT (up to 250mA) HIGH RIPPLE REJECTION HIGH LOAD REGULATION HIGH LINE REGULATION SHORT CIRCUIT PROTECTION THERMAL SHUT DOWN WITH HYSTERESIS DUMP PROTECTION DESCRIPTION This circuit combines both a filter and a voltage regulator in order to provide a high ripple rejection over a wide input voltage range. A supervisor low-pass loop of the element prevents the output transistor from saturation at low input voltage. The non linear behaviour of this control circuitry allows a fast settling of the filter. POWER MINIDIP ORDERING NUMBER : L4915 PIN CONNECTION June1993 1/7 L4915 BLOCK DIAGRAM ABSOLUTE MAXIMUM RATINGS Symbol Vi Vi IO Ptot Tstg Parameter Peak Input Voltage (300 ms) DC Input Voltage Output Current Power Dissipation Storage and Junction Temperature Value 40 28 Internally Limited Internally Limited – 40 to 150 Unit V V Value 80 20 Unit °C/W °C/W °C THERMAL DATA Symbol Rth j-amb R th j-pins Parameter Thermal Resistance Junction-ambient Thermal Resistance Junction-pins Max. Max. ELECTRICAL CHARACTERISTICS (Tamb = 25oC; Vi = 13.5 V, VO = 8.5V, circuit of Fig. 1, unless otherwise specified) Symbol Vi Vo ∆VI/O ∆VO ∆Vo 2/7 Parameter Input Voltage Output Voltage Controlled Input-output Dropout Voltage Line Regulation Load Regulation ∆Vo Load Regulation (filter mode) Vref Iq ∆Iq IAD Internal Voltage Reference Quiescent Current Quiescent Current Change Adjust Input Current Test Conditions Vi = 6 to 18V, Io = 5 to 150mA Io = 5 to 150mA, Vi = 6 to 10V Vi = 12 to 18V, Io = 10mA Io = 5 to 250mA, ton = 30µs, toff = ≥ 1ms Vi = 8.5V, Io = 5 to 150mA ton = 30µs, toff =≥ 1ms Io = 5 mA Vi = 6 to 18V, Io = 5 to 150mA Min. Typ. 1.6 1 50 Max. 20 11 2.1 20 100 Unit V V V mV mV 150 250 mV 4 2.5 1 0.05 40 2 V mA mA nA L4915 ELECTRICAL CHARACTERISTICS (continued) (Tamb = 25oC; Vi = 13.5 V, VO = 8.5V, circuit of Fig. 1, unless otherwise specified) Symbol ∆VO ∆T SVR ISC Ton Tj Parameter Test Conditions Output Voltage Drift Io = 10mA Supply Voltage Rejection Viac = 1VRMS, f = 100Hz, Io = 150mA Regulator Filter Mode Short Circuit Current Switch On Time Min. 1.2 Max. Unit mV/°C dB 250 Io = 150mA Regulator Filter Mode Thermal Shutdown Junction Temperature Typ. 71 35(*) 300 300 500(*) 145 mA ms °C (*) Depending of the CFT 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 uses a PNP-NPN connection to reduce the dropout. The reference voltage of the OP1 is derived from a REF through the 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 Figure 1). Figure 1 : Nonliner Transfer Characteristic of the Drop Control Unit the contrary, a control loop on the L4915 consents to avoid the saturation of the series element by regulating the value of the reference voltage (pin 2). In fact, whenever the input voltage decreases below (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 characteristic. The ripple rejection is externally adjustable acting on CFT as follows : Vi (jΩ) 10−6 SVR (jΩ) = =1+ R1 gm VOUT (jΩ) 1 + jw C R2 FT Where: gm = 2 ⋅ 10-5 Ω-1 = OTA’S typical transconductance value on linear region R1 = fixed ratio R2 CFT = value of capacitor in µF The output voltage is fixed to its nominal value : R1 R1 VOUT NOM = VREF 1 + = VCFT 1 + R2 R2 The ripple rejection is quite high (70dB) and independent to CFT value. On the usual voltage regulators, when the input vol-tage goes below the nominal value, the regulation transistors (series element) saturate bringing the system out of regulation and making it very sensible to every variation of the input voltage. On The reaction time of the supervisor loop is given by the transconductanceof the OTAand by CFT. When the value of the ripple voltage is 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 transconductance condition [range (3) of the characteristic] and discharges 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 = 10µF; f = 100Hz; Vo = 8.5V a SVR of 35 is obtained. 3/7 L4915 Figure 2 : Supply Voltage Rejection versus Input Voltage Figure 3 : Supply Voltage Rejection versus Frequency Figure 4 : VO versus Supply Voltage (VO = 8.5V) Figure 5 : Quiescent Current versus Input Voltage (VO = 8.5V) Figure 6 : Dropout versus Load Current 4/7 L4915 APPLICATION CIRCUIT 5/7 L4915 MINIDIP 4+4 PACKAGE MECHANICAL DATA mm DIM. MIN. A TYP. MAX. MIN. 3.3 TYP. MAX. 0.130 a1 0.7 B 1.39 1.65 0.055 0.065 B1 0.91 1.04 0.036 0.041 b b1 0.028 0.5 0.38 0.020 0.5 D 0.015 0.020 9.8 0.386 E 8.8 0.346 e 2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 F 7.1 0.280 I 4.8 0.189 L Z 6/7 inch 3.3 0.44 0.130 1.6 0.017 0.063 L4915 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 inlife 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. 7/7