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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. PIN CONNECTION
POWER MINIDIP ORDERING NUMBER : L4915
June1993
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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
C
THERMAL DATA
Symbol Rth j-amb R th j-pins Parameter Thermal Resistance Junction-ambient Thermal Resistance Junction-pins Max. Max. Value 80 20 Unit C/W C/W
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 Vo Vref Iq Iq IAD 2/7 Parameter Input Voltage Output Voltage Controlled Input-output Dropout Voltage Line Regulation Load Regulation Load Regulation (filter mode) 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 = 30s, toff = 1ms Vi = 8.5V, Io = 5 to 150mA ton = 30s, toff = 1ms Io = 5 mA Vi = 6 to 18V, Io = 5 to 150mA Min. 4 1.6 1 50 150 2.5 1 0.05 40 Typ. Max. 20 11 2.1 20 100 250 Unit V V V mV mV mV V mA mA nA
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L4915
ELECTRICAL CHARACTERISTICS (continued) (Tamb = 25oC; Vi = 13.5 V, VO = 8.5V, circuit of Fig. 1, unless otherwise specified)
Symbol VO T SVR Parameter Output Voltage Drift Supply Voltage Rejection Test Conditions Io = 10mA Viac = 1VRMS, f = 100Hz, Io = 150mA Regulator Filter Mode 250 Io = 150mA Regulator Filter Mode Min. Typ. 1.2 71 35(*) 300 300 500(*) 145 Max. Unit mV/C dB
ISC Ton Tj
Short Circuit Current Switch On Time
mA ms C
Thermal Shutdown Junction Temperature
(*) 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 (j) 10-6 SVR (j) = = 1 + gm R1 VOUT (j) 1 + R2 jw C FT
Where: gm = 2 10-5 -1 = OTA'S typical transconductance value on linear region R1 = fixed ratio R2 CFT = value of capacitor in F 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 = 10F; f = 100Hz; Vo = 8.5V a SVR of 35 is obtained.
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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
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
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L4915
APPLICATION CIRCUIT
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L4915
MINIDIP 4+4 PACKAGE MECHANICAL DATA
DIM. MIN. A a1 B B1 b b1 D E e e3 e4 F I L Z 0.44 3.3 1.6 0.017 8.8 2.54 7.62 7.62 7.1 4.8 0.130 0.063 0.38 0.7 1.39 0.91 0.5 0.5 9.8 0.346 0.100 0.300 0.300 0.280 0.189 0.015 1.65 1.04 mm TYP. 3.3 0.028 0.055 0.036 0.020 0.020 0.386 0.065 0.041 MAX. MIN. inch TYP. 0.130 MAX.
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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. (c) 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.
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