L4916 june 2000 voltage regulator plus filter ? . fixed output voltage 8.5 v . 250 ma output current . high ripple rejection . high load regulation . high line regulation . short circuit protection . thermal shut down with hysteresis . dump protection this circuit combines both a filter and a voltage regu- lator 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 volt- ages. the non linear behaviour of this control circuitry allows a fast settling of the filter. power minidip (4 + 4) ordering number : L4916 block diagram description 1/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
absolute maximum ratings symbol parameter value unit v i peak input voltage (300 ms) 40 v v i dc input voltage 28 v i o output current internally limited p tot power dissipation internally limited t stg , t j storage and junction temperature C 40 to 150 c pin connection (top view) thermal data symbol parameter value unit r th j-amb r th j-pins thermal resistance junction-ambient thermal resistance junction-pins max max 80 20 c/w c/w L4916 2/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
electrical characteristics (t amb = 25 c; v i = 13.5 v, test circuit of fig. 1, unless otherwise specified) symbol parameter test conditions min. typ. max. unit v i input voltage 20 v v o output voltage v i = 12 to 18 v i o = 5 to 150 ma 8.1 8.5 8.9 v d v i/o controlled input-output dropout voltage v i = 5 to 10 v i o = 5 to 150 ma 1.6 2.1 v d v o line regulation v i = 12 to 18 v i o = 10 ma 120mv d v o load regulation i o = 5 to 250 ma t on = 30 m s t off = 3 1 ms 50 100 mv d v o load regulation (filter mode) v i = 8.5 v i o = 5 to 150 ma t on = 30 m s t off = 3 1 ms 150 250 mv i q quiescent current i o = 5 ma 1 2 ma d i q quiescent current change v i = 6 to 18 v i o = 5 to 150 ma 0.05 ma d v o d t output voltage drift i o = 10 ma 1.2 mv/ c svr supply voltage rejection v iac = 1 v rms f = 100 hz i o = 150 ma v idc = 12 to 18 v v idc = 6 to 11 v 70 35(*) db db i sc short circuit current 250 300 ma t on switch on time i o = 150 ma v i = 5 to 11 v v i = 11 to 18 v 500(*) 300 ms ms t j thermal shutdown junction temperature 145 c (*) depending of the c ft capacitor. figure 1 : test and application circuit. L4916 3/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
figure 2 : p.c. board and component layout of fig. 1 (1 : 1 scale). principle of operation during normal operation (input voltage upper than v i min = v out nom + d v i/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 connec- tion 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 v ref . in this condition the device works in the range (1) of the characteristic of the non linear drop control unit (see fig.3). the output voltage is fixed to its nominal value: r1 v out nom = v ref (1 + ) = r2 r1 v cft (1 + ) r2 r1 = internally fixed ratio = 2.4 r2 the ripple rejection is quite high (70 db) and inde- pendent from c ft 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 making it very sensible to every variation of the input voltage. on the contrary, a control loop on the L4916 consents to avoid the saturation of the series element by regulating the value of the reference voltage (pin 2). in fact, when- ever the input voltage decreases below v i min the supervisor loop, utilizing a non linear ota, forces the reference voltage at pin 2 to decrease by dis- charging c ft . so, during the static mode, when the input voltage goes below v min the drop out is kept fixed to about 1.6v. in this condition the device works as a low pass filter in the range (2) of the ota characteristic. the ripple rejection is externally ad- justable acting on c ft as follows : v i (jw) svr (jw) = = v out (jw) 10 -6 1 + gm r1 (1 + ) jwc ft r 2 where: gm = 2 . 10 -5 w -1 = otas typical transconductance value on linear region r1 = fixed ratio r2 c ft = value of capacitor in m f the reaction time of the supervisor loop is given by the transconductance of the ota and by c ft . when the value of the ripple voltage is so high and its ne- gative peak is fast enough to determine an istanta- neous decrease of the dropout till 1.2 v, the ota works in a higher transconductance condition [range (3) of the characteristic] and discharge the capacitor rapidously. if the ripple frequency is high enough the capacitor wont charge itself completely, and the output volt- age reaches a small value allowing a better ripple re- jection ; the devices again working as a filter (fast transient range). with c ft = 10 m f; f = 100 hz a svr of 35 is obtained. L4916 4/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
figure 3 : nonliner transfer characteristic of the drop control unit. figure 4 : supply voltage rejection vs. input voltage. figure 5 : supply voltage rejection vs. frequency. figure 6 : v o vs. supply voltage. figure 7 : quiescent current vs. input voltage. 1) normal operating range (high ripple rejection) 2) drop controlled range (medium ripple rejection) 3) fast discharge of c ft L4916 5/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
figure 8 : dropout vs. load current. figure 9 : inhibit function realized on c ft pin. L4916 6/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
powerminidip dim. mm inch min. typ. max. min. typ. max. a 3.3 0.130 a1 0.7 0.028 b 1.39 1.65 0.055 0.065 b1 0.91 1.04 0.036 0.041 b 0.5 0.020 b1 0.38 0.5 0.015 0.020 d 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 3.3 0.130 z 0.44 1.6 0.017 0.063 outline and mechanical data L4916 7/8 obsolete product(s) - obsolete product(s) obsolete product(s) - obsolete product(s)
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