1/9 may 2001 n regulated 5v 4% charge pump n output current guaranteed over temperature : 20ma (v i 2v ), 30ma (v i 3v ) n no inductors; very low emi noise n uses small, inexpensive capacitors n logic controlled 1 m a max shut-down supply current n shut down disconnects load from input n available in so-8 and dip-8 packages description the st619lb is a step-up charge pump dc-dc converter which delivers a regulated 5v 4% output at 30ma and over temperature. the input voltage range is 2v to 3.6v (two battery cells). it requires only four external capacitor: two 0.22 m f flying capacitors, and 10 m f capacitors at the input and output. low operating supply current (typ 200 m a) make the device ideal for small, portable and battery powered applications. when shut down the load is disconnected from the input and the supply current is typically 0.02 m a. the st619lb is available in so-8 and dip-8 packages. st619lb series dc-dc converter regulated 5v charge pump schematic diagram dip-8 so-8
st619lb series 2/9 operating principle the st619lb is able to provide a regulated 5v output from a 2v to 3.6v (two battery cells) input. internal charge pump and external capacitors generate the 5v output, eliminating the need for inductors. the output voltage is regulated to 5v, 4% by a pulse skipping controller that turns on the charge pump when the output voltage begins to drop. to maintain the greatest efficiency the internal charge pump of the device operates as a voltage doubler when v i ranges from 3.0v to 3.6v and as a voltage tripler when v i ranges from 2.0v to 2.5v. when v i ranges from 2.5v to 3.0v , the st619lb switches between doubler and tripler mode on alternating cycles, making a 2.5 x v i charge pump. to further enhance the efficiency over the input range, an internal comparator selects the higher of v i or v o to run the st619lb's circuitry. with v i = 2v and i o = 20ma the typical efficiency value is 80%. in tripler mode (see block diagram), when the s1 switches close, the s2 switches open and capacitors c1 and c2 charge up to v i .onthe second half of the cycle, c1 and c2 are connected in series between in and out when the s1 switches open and s2 switches close. in the doubler mode only c2 is used. during one oscillator cycle, energy is transferred from the input to the charge pump capacitors, and then from the charge pump capacitors to the output capacitors and load. the number of cycles within a given time frame increases as the load increases or as the input supply voltage decreases. in the limiting case , the charge pumps operate continuously, and the oscillator frequency is nominally 500khz. shut down mode the st619lb enters low power shut down mode when shdn is a logic high. in shut down mode, out is disconnected from the in and v o falls to 0v. the shdn pin is connected to ground for normal operation. shdn is a cmos compatible input. absolute maximum ratings absolute maximum ratings are those values beyond which damage to the device may occur. functional operation under these condition is not implied. thermal data (*) this value depends from thermal design of pcb on which the device is mounted. symbol paramet er value unit v i dc input voltage -0.3 to 5.5 v v o output voltage -0.3 to 5.5 v v shdn shutdown input voltage -0.3 to (v i + 0.3) v i o output current continuous 120 ma t stg storage temperature range -55 to +150 c t op operating junction temperature range -40 to +85 c symbol parameter so-8 dip-8 unit r thj-amb thermal resistance junction-ambient (*) 160 100 c/w
st619lb series 3/9 connection diagram (top view) ordering codes pin description electrical characteristics (v i =2 to 3.6v, c 1 =c 2 =0.22 m f, c 3 =c 4 =10 m f, t a = -40 to 85 c, unless otherwise specified. typical value are referred at t a =25 c) note: do not overload or short the output to ground. if the above conditions are not observed the device may be damaged. type dip-8 so-8 so-8 (t&r) st619lb ST619LBN st619lbd st619lbdr pin n symbol name and function 1 c1+ positive terminal for the first charge pump capacitor 2 in input supply voltage 3 out 5v output voltage. v o =0v when in shutdown mode. 4 c2+ positive terminal for the second charge pump capacitor 5 c2- negative terminal for the second charge pump capacitor 6 gnd ground 7 shdn active high c-mos logic level shutdown input. shdn is connected to gnd for normal operation. 8 c1- negative terminal for the first charge pump capacitor symbol parameter test conditions min. typ. max. unit v i input voltage 2 3.6 v v o output voltage v i = 2 to 3.6v i o =0 to 20ma v i = 3 to 3.6v i o =0 to 30ma 4.8 4.8 5 5 5.2 5.2 v v v ripple output voltage ripple no load, full load 100 mv i i no load supply current v i = 2 to 3v no load v i = 3 to 3.6v no load 200 75 300 150 m a m a i shdn shutdown supply current v i = 2 to 3.6v no load v shdn =v i 0.02 1 m a n efficency v i =3v i o =20ma v i =3v i o =30ma v i =2v i o =20ma 82 82 80 % % % f osc switching frequency full load 500 khz v ih shdn input threshold 0.7v i v v il shdn input threshold 0.4 v i ih shdn input current v shdn =v i 0.005 1 m a
st619lb series 4/9 typical performance characteristics (unless otherwise specified t a =25 c) figure 1 : no load supply current vs input voltage figure 2 : shutdown supply current vs input voltage figure 3 : maximum output current vs input voltage figure 4 : output voltage vs output current figure 5 : efficency vs output current figure 6 : efficency vs input voltage
st619lb series 5/9 figure 7 : output voltage vs input voltage figure 8 : start-up figure 9 : output voltage vs temperature figure 10 : line transient response figure 11 : load transient response r l =250 w v i =3v, i o =0 to 25ma
st619lb series 6/9 application information charge pump capacitors c1 and c2 the values of charge pump capacitors c1 and c2 are critical to ensure adequate output current and avoid excessive peak currents. it is suggested to use values in the range of 0.22 m f to 1.0 m fand avoid the use of higher values of c o capacitors, in order to obtain best performance. ceramic or tantalum capacitors are recommended. input and output capacitors c3 and c4 the type of input capacitor (c3) and output filter capacitor (c4) used is not critical, but it does affect performance. tantalums, ceramics or aluminium electrolytic are suggested. for lowest ripple, use large, low effective series resistance (esr) ceramic tantalum capacitors. if the input supply source impedance is very low, c3 can be omitted. the typical application circuit shows the component values for proper operation using minimal board space. the input bypass capacitor (c3) and output filter capacitor (c4) should be at least 10 m f. many capacitors exhibit 40% to 50% variation over temperature. compensate for capacitor temperature coefficient by selecting a large nominal value to ensure proper operation over temperature. layout consideration in the below figure, the typical application demoboard of st619lb is reported. a good layout ensures stability and helps maintain the output voltage under heavy loads. for best performance, use very short connections to the capacitors. typical application circuit typical application demoboard
|
