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april 2009 doc id 13959 rev 5 1/12 12 A6902D up to 1 a step down switch ing regulator with adjustable current limit for automotive applications features qualified following the aec-q100 requirements (see ppap for more details) up to 1 a dc output current operating input voltage from 8 v to 36 v output voltage adjustable from 1.235 v to 35 v precise 3.3 v (2 %) reference voltage 250 khz internally fixed frequency voltage feedforward zero-load current operation internal current limiting protection against feedback disconnection thermal shutdown applications automotive applications adjustable current generator simple step-down converters with adjustable current limit so-8 figure 1. application schematic r1 5.6k o r2 3.3ko r3 5.1ko rsense 100m o c1 10f 35v c2 22nf c3 220pf c4 100 f 10v l1 22h d1 stps340u l6902d v cc v ref comp gnd fb out cs+ cs- v in =8v to 36v v out =3.3v v in =8v to 36v r1 5.6k o r2 3.3ko r3 5.1ko rsense 100m o c1 10f 35v c2 22nf c3 220pf c4 100 f 10v l1 22h d1 stps340u l6902d v cc v ref comp gnd fb out cs+ cs- v in =8v to 36v v out =3.3v v in =8v to 36v www.st.com
contents A6902D 2/12 doc id 13959 rev 5 contents 1 description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1 maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
A6902D description doc id 13959 rev 5 3/12 1 description the A6902D is a complete and simple step down switching regulator with adjustable current limit. based on a voltage mode structure it integrates a current error amplifier to have a constant voltage and constant current control . by means of an on board current sense resistor and the availability of the current sense pins (both compatible to vcc and for cs- compatible with gnd too) a cu rrent limit programming is very simple and accurate. moreover constant current control can be used to charge nimh and nicd batteries.the device can be used as a standard dc/dc converter with adjustable current limit (set by using the external sense resistor). the inte rnal robust p-channel dmos transistor with a typical of 250 m assures high efficiency and a minimum dropout even at high output current level. the internal limiting current (latched function) of typical value of 2.5 a protects the device from accidental output short circ uit avoiding dangerous loads damage. if the temperature of the chip goes higher than a fixed internal threshold (150 c with 20 c hysteresis), the power stage is turned off. other protections beside thermal shutdown complete the device for a safe and reliable application: overvoltage protection, frequency folback overcurrent protection and protection vs. feedback disconnection. the internal fixed switching frequency of 250 khz, and the so-8 package pin allow to built an ultra compact dc/dc converter with a minimum board space.
pin connection A6902D 4/12 doc id 13959 rev 5 2 pin connection 2.1 pin connection figure 2. pin connection (top view) 2.2 pin description table 1. pin description n pin description 1 out regulator output. 2 cs+ current error amplifier input (c urrent sense at higher voltage) 3 cs- current error amplifier input (current sense at lower voltage) 4 comp e/a output for frequency compensation. 5fb feedback input. connecting directly to this pin results in an output voltage of 1.23 v. an extenal resist ive divider is required for higher output voltages. 6v ref 3.3 v reference voltage. no cap is need for stability. 7 gnd ground. 8 vcc unregulated dc input voltage.
A6902D electrical data doc id 13959 rev 5 5/12 3 electrical data 3.1 maximum ratings 3.2 thermal data table 2. absolute maximum ratings symbol parameter value unit v 8 input voltage 40 v v 1 out pin dc voltage out pin peak voltage at t = 0.1 s -1 to 40 -5 to 40 v v i 1 maximum output current int. limit. v 4 , v 5 analog pins 4 v v 2 , v 3 analog pins -0.3 to v cc v p tot power dissipation at t a 70 c 0.7 w t j operating junction temperature range -40 to 150 c t stg storage temperature range -55 to 150 c table 3. thermal data symbol parameter so8 unit r thja maximum thermal resistance junction-ambient 110 (1) 1. package mounted on board c/w
electrical characteristics A6902D 6/12 doc id 13959 rev 5 4 electrical characteristics t j = -40 to 125 c, v cc = 12 v, unless otherwise specified table 4. electrical characteristics symbol parameter test conditions min. typ. max. unit v cc operating input voltage range v 0 = 1.235 v; i 0 = 2 a 8 36 v r ds(on) mosfet on resistance 0.250 0.5 i l maximum limiting current (1) v cc = 8.5 v 1.8 2.5 3.2 a v cc = 8.5 v, t j = 25 c 2 2.5 3.2 f sw switching frequency 212 250 280 khz duty cycle 0 100 % dynamic characteristics (see test circuit) v 5 voltage feedback 8 v < v cc < 36 v, 20 ma < i 0 < 1 a 1.198 1.235 1.272 v efficiency v 0 = 5 v, v cc = 12 v 90 % dc characteristics i qop total operating quiescent current 35ma i q quiescent current duty cycle = 0; v fb = 1.5 v 2.7 ma error amplifier v oh high level output voltage v fb =1 v 3.6 v v ol low level output voltage v fb =1.5 v 0.4 v i o source source output current v comp = 1.9 v; v fb = 1 v 160 300 a i o sink sink output current v comp = 1.9 v; v fb = 1.5 v 11.5 ma i b source bias current 2.5 4 a dc open loop gain r l = 50 58 db gm transconductance i comp = -0.1 ma to 0.1 ma; v comp = 1.9 v 2.3 ms v offs input offset voltage v cs- = 1.8 v; v cs+ = v comp 90 100 110 mv i cs+ cs+ output current i 0 =1 a; r sense =100 m ; v out < v cc -2 v 1.5 3 a i cs- cs- output current i 0 =1a; r sense =100 m ; v out < v cc -2 v 1.5 3 a 8
A6902D electrical characteristics doc id 13959 rev 5 7/12 reference section reference voltage i ref = 0 to 5 ma v cc = 8 v to 36 v 3.2 3.3 3.399 v line regulation i ref = 0ma v cc = 8 v to 36 v 510mv load regulation i ref = 0 to 5 ma 8 15 mv short circuit current 5 18 35 ma 1. with t j = 85 c, i lim_min = 2 a, assured by design, characte rization and statistical correlation. table 4. electrical characteristics (continued) symbol parameter test conditions min. typ. max. unit
package mechanical data A6902D 8/12 doc id 13959 rev 5 5 package mechanical data in order to meet environmental requirements, st offers these devices in different grades of ecopack ? packages, depending on their level of environmental compliance. ecopack ? specifications, grade definitions and product status are available at: www.st.com . ecopack ? is an st trademark.
A6902D package mechanical data doc id 13959 rev 5 9/12 figure 3. package dimensions table 5. so-8 mechanical data dim mm inch min. typ. max. min. typ. max. a 1.35 1.75 0.053 0.069 a1 0.10 0.25 0.004 0.010 a2 1.10 1.65 0.043 0.065 b 0.33 0.51 0.013 0.020 c 0.19 0.25 0.007 0.010 d (1) 1. 1. dimension d does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.15 mm (0.006 inch) in total (both side). 4.80 5.00 0.189 0.197 e 3.80 4.00 0.15 0.157 e1.27 0.050 h 5.80 6.20 0.228 0.244 h 0.25 0.50 0.010 0.020 l 0.40 1.27 0.016 0.050 k0 (min), 8 (max) ddd 0.10 0.004
order codes A6902D 10/12 doc id 13959 rev 5 6 order codes table 6. ordering information order codes package packaging A6902D so-8 tu b e A6902D13tr tape and reel
A6902D revision history doc id 13959 rev 5 11/12 7 revision history table 7. document revision history date revision changes 02-oct-2007 1 initial release 5-nov-2007 2 updated: table 4 on page 6 2-may-2008 3 updated: table 4 on page 6 28-aug-2008 4 updated: coverpage and table 4 on page 6 23-apr-2009 5 updated first feature in coverpage
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