? semiconductor components industries, llc, 2002 march, 2002 rev. 3 1 publication order number: ncp345/d ncp345 over voltage protection ic the ncp345 overvoltage protection circuit (ovp) protects sensitive electronic circuitry from overvoltage transients and power supply faults when used in conjunction with an external pchannel fet. the device is designed to sense an overvoltage condition and quickly disconnect the input voltage supply from the load before any damage can occur. the ovp consists of a precise voltage reference, a comparator with hysteresis, control logic, and a mosfet gate driver. the ovp is designed on a robust bicmos process and is intended to withstand voltage transients up to 30 v. the device is optimized for applications that have an external ac/dc adapter or car accessory charger to power the product and/or recharge the internal batteries. the nominal overvoltage threshold is 6.85 v so it is suitable for single cell liion applications as well as 3/4 cell nicd/nimh applications. features ? overvoltage turnoff time of less than 1.0 m sec ? accurate voltage threshold of 6.85 v (nominal) ? undervoltage lockout protection ? cntrl input compatible with 1.8 v logic levels typical applications ? cellular phones ? digital cameras ? portable computers and pdas ? portable cd and other consumer electronics - + out in v ref gnd cntrl + v cc logic fet driver undervoltage lock out load ac/dc adapter or accessory charger c1 schottky diode microprocessor port pch figure 1. simplified application diagram ncp345 note: this device contains 89 active transistors thin sot235 sn suffix case 483 1 http://onsemi.com 5 pin connections & marking diagram 1 3 in out 2 gnd cntrl 4 vcc 5 (top view) device package shipping ordering information ncp345snt1 thin sot235 3000 / 7 reel radyw y = year w = work week
ncp345 http://onsemi.com 2 figure 2. detailed block diagram - + cntrl (3) out (1) gnd (2) - + logic block driver pre regulator v cc (5) in (4) on/off uvlo out v5 vcc vcc r1 r2 r3 r4 comp bandgap reference pin function descriptions pin # symbol pin description 1 out this signal drives the gate of a pchannel mosfet. it is controlled by the voltage level on in or the logic state of the cntrl input. when an overvoltage event is detected, the out pin is driven to within 1.0 v of v cc in less than 1.0 m sec provided that gate and stray capacitance is less than 12 nf. 2 gnd circuit ground 3 cntrl this logic signal is used to control the state of out and turnon/off the pchannel mosfet. a logic high results in the out signal being driven to within 1.0 v of vcc which disconnects the fet. if this pin is not used, the input should be connected to ground. 4 in this pin senses an external voltage point. if the voltage on this input rises above the overvoltage threshold (vth), the out pin will be driven to within 1.0 v of vcc, thus disconnecting the fet. the nominal threshold level is 6.85 v and this threshold level can be increased with the addition of an external resistor between in and v cc . 5 vcc positive voltage supply. if vcc falls below 2.8 v (nom), the out pin will be driven to within 1.0 v of vcc, thus disconnecting the pchannel fet. truth table in cntrl out v th l vcc >v th h vcc
ncp345 http://onsemi.com 3 absolute maximum ratings* (t a = 25 c unless otherwise noted.) rating pin symbol min max unit out voltage to gnd 1 v o 0.3 30 v input and cntrl pin voltage to gnd 4 3 v input v cntrl 0.3 0.3 30 13 v v cc maximum range 5 v cc(max) 0.3 30 v maximum power dissipation at t a = 85 c p d 0.216 w thermal resistance junction to air r ja 300 c/w junction temperature t j 150 c operating ambient temperature t a 40 85 c v cntrl operating voltage 3 0 5.0 v storage temperature range t stg 65 150 c esd performance (hbm) all 2.5 kv * maximum ratings are those values beyond which damage to the device may occur. human body model (hbm): mil std 883c method 30157, (r = 1500 ohms, c = 100 pf, f = 3 pulses delay 1 s). electrical characteristics (for typical values t a = 25 c, for min/max values t a = 40 c to +85 c, v cc = 6.0 v, unless otherwise noted.) characteristic symbol pin min typ max unit v cc operating voltage range v cc(opt) 5 3.0 4.8 25 v supply current (i cc + i input ; v cc = 6.0 v steady state) 4,5 0.75 1.0 ma input threshold (v input connected to v cc ; v input increasing) v th 4 6.65 6.85 7.08 v input hysteresis (v input connected to v cc ; v input decreasing) v hyst 4 50 100 200 mv input impedance (input = v th ) r in 4 70 150 k cntrl voltage high v ih 3 1.5 v cntrl voltage low v il 3 0.5 v cntrl current high (v ih = 5.0 v) i ih 3 95 200 m a cntrl current low (v il = 0.5 v) i il 3 10 20 m a under voltage lockout (v cc decreasing) v lock 3 2.5 2.8 3.0 v output sink current (v cc < v th , v out = 1.0 v) i sink 1 10 33 50 m a output voltage high (v cc = v in = 8.0 v; i source = 10 ma) output voltage high (v cc = v in = 8.0 v; i source = 0.25 ma) output voltage high (v cc = v in = 8.0 v; i source = 0 ma) v oh 1 v cc 1.0 v cc 0.25 v cc 0.1 v output voltage low (input < 6.5 v; i sink = 0 ma; v cc = 6.0 v, cntrl = 0 v) v ol 1 0.1 v turn on delay input (v input connected to v cc ; v input step down signal from 8.0 to 6.0 v; measured to 50% point of out)* t on in 1 10 m sec turn off delay input (v input connected to v cc ; v input step up signal from 6.0 to 8.0 v; c l = 12 nf output > v cc 1.0 v) t off in 1 0.5 1.0 m sec turn on delay cntrl (cntrl step down signal from 2.0 to 0.5 v; measured to 50% point of out)* t on ct 1 10 m sec turn off delay cntrl (cntrl step up signal from 0.5 to 2.0 v; c l = 12 nf output > v cc 1.0 v) t off ct 1 1.0 2.0 m sec *turn on delay is guaranteed by design.
ncp345 http://onsemi.com 4 40 ambient temperature ( c) 25 10 5 20 35 50 65 80 95 50 45 40 35 30 25 20 15 10 sink current ( a) 1.0 0.9 0.8 0.7 0.6 0.5 40 25 10 5 20 35 50 65 80 95 temperature ( c) 7.05 7.00 6.95 6.90 6.85 6.80 6.75 6.70 40 25 10 5 20 35 50 65 80 95 ambient temperature ( c) voltage (v) i supply (ma) voltage (v) 50 100 150 200 250 300 350 400 450 500 2 1 0 6 4 2 0 time (nsec) t = 25 c v load cntrl v load = 50 w mosfet = mgsf3441 voltage (v) 5 101520253035404550 2 1 0 6 4 2 0 time ( m sec) t = 25 c v load cntrl v load = 50 w mosfet = mgsf3441 figure 3. typical v th threshold variation vs. temperature figure 4. typical out sink current vs. temperature v in v th , v out 1 v figure 5. typical supply current vs. temperature i cc i in , v cc 6 v figure 6. typical turnoff time cntrl to v load figure 7. typical turnon time cntrl to v load
ncp345 http://onsemi.com 5 application information - + out in v ref gnd cntrl + v cc logic fet driver undervoltage lock out load ac/dc adapter or accessory charger zener diode (optional) c1 schottky diode microprocessor port pch ncp345 zener diode (optional) figure 8. introduction in many electronic products, an external ac/dc wall adapter is used to convert the ac line voltage into a regulated dc voltage or a current limited source. line surges or faults in the adapter may result in overvoltage events that can damage sensitive electronic components within the product. this is becoming more critical as the operating voltages of many integrated circuits have been lowered due to advances in submicron silicon lithography. in addition, portable products with removable battery packs pose special problems since the pack can be removed at any time. if the user removes a pack in the middle of charging, a large transient voltage spike can occur which can damage the product. finally, damage can result if the user plugs in the wrong adapter into the charging jack. the challenge of the product designer is to improve the robustness of the design and avoid situations where the product can be damaged due to unexpected, but unfortunately, likely events that will occur as the product is used. circuit overview to address these problems, the protection system above has been developed consisting of the ncp345 over voltage protection ic and a pchannel mosfet switch such as the mgsf3441. the ncp345 monitors the input voltage and will not turn on the mosfet unless the input voltage is within a safe operating window that has an upper limit of 7.05 v. a zener diode can be placed in parallel to the load to provide for secondary protection during the brief time that it takes for the ncp345 to detect the overvoltage fault and disconnect the mosfet. the decision to use this secondary diode is a function of the charging currents expected, load capacitance across the battery, and the desired protection voltage by analyzing the dv/dt rise that occurs during the brief time it takes to turnoff the mosfet. for battery powered applications, a lowforward voltage schottky diode such as the mbrm120lt3 can be placed in series with the mosfet to block the body diode of the mosfet and prevent shorting the battery out if the input is accidentally shorted to ground. this provides additional voltage mar gin at the load since there is a small forward drop across this diode that reduces the voltage at the load. when the protection circuit turns off the mosfet, there can be a sudden rise in the input voltage of the device. this transient can be quite large depending on the impedance of the supply and the current being drawn from the supply at the time of an overvoltage event. this inductive spike can be clamped with a zener diode from in to ground. this diode breakdown voltage should be well above the worst case supply voltage provided from the ac/dc adapter or cigarette lighter adapter (cla), since the zener is only intended to clamp the transient. the ncp345 is designed so that the in and v cc pin can safely protect up to 25 v and withstand transients to 30 v. since these spikes can be very narrow in duration, it is important to use a high bandwidth probe and oscilloscope when prototyping the product to verify the operation of the circuit under all the transient conditions. a similar problem can result due to contact bounce as the dc source is plugged into the product. for portable products it is normal to have a capacitor to ground in parallel with the battery. if the product has a battery pack that is easily removable during charging, this scenario should be analyzed. under that situation, the charging current will go into the capacitor and the voltage may rise rapidly depending on the capacitor value, the charging current and the power supply response time.
ncp345 http://onsemi.com 6 normal operation figure 1 illustrates a typical configuration. the external adapter provides power to the protection system so the circuitry is only active when the adapter is connected. the ovp monitors the voltage from the charger and if the voltage exceeds a nominal voltage of 6.85 v, the out signal drives the gate of the mosfet to within 1.0 v of vcc, thus turning off the fet and disconnecting the source from the load. the nominal time it takes to drive the gate to this state is 400 nsec (1.0 usec maximum for gate capacitance of < 12 nf). typical turn off performance using the cntrl input can be seen in figure 6. the cntrl input can also be used to interrupt charging and allow the microcontroller to measure the cell voltage under a normal condition to get a more accurate measure of the battery voltage. once the over voltage is removed, the ncp345 will turn on the mosfet. the turn on circuitry is designed to turn on the mosfet more gradually to limit the inrush current. typical turnon performance is illustrated using the mgsf3441 in figure 7. this characteristic is a function of the threshold of the mosfet and will vary depending on the device characteristics such as the gate capacitance. the ovp has an under voltage lockout (uvlo) circuit which disables the gate driver circuit until the uvlo senses that the vcc voltage is above 2.6 v. once the uvlo has released the gate driver circuit, the out signal will stay high until the voltage on the in is sensed. if the input voltage to in is less than 6.85 v nominal, then the out signal will be driven low and the fet will be turned on so the source can be connected to the load. there are three events that will cause the ovp to drive the gate of the fet to a high state. voltage on vcc falls below the uvlo threshold voltage on in rises above 6.85 v (nominal) cntrl input is driven to a logic high
ncp345 http://onsemi.com 7 information for using the thin sot235 surface mount package minimum recommended footprint for surface mounted applications surface mount board layout is a critical portion of the total design. the footprint for the semiconductor packages must be the correct size to insure proper solder connection interface between the board and the package. with the correct pad geometry, the packages will self align when subjected to a solder reflow process. mm inches 1.9 0.039 1.0 0.094 0.7 0.074 2.4 0.028 0.95 0.037 0.95 0.037 thin sot235 thin sot235 power dissipation the power dissipation of the thin sot235 is a function of the pad size. this can vary from the minimum pad size for soldering to a pad size given for maximum power dissipation. power dissipation for a surface mount device is determined by t j(max) , the maximum rated junction temperature of the die, r q ja , the thermal resistance from the device junction to ambient, and the operating temperature, t a . using the values provided on the data sheet for the thin sot235 package, p d can be calculated as follows: p d t j(max) t a r ja the values for the equation are found in the maximum ratings table on the data sheet. substituting these values into the equation for an ambient temperature t a of 25 c, one can calculate the power dissipation of the device which in this case is 400 milliwatts. p d 150 c25 c 300 c w 417 milliwatts the 300 c/w for the thin sot235 package assumes the use of the recommended footprint on a glass epoxy printed circuit board to achieve a power dissipation of 417 milliwatts. soldering precautions the melting temperature of solder is higher than the rated temperature of the device. when the entire device is heated to a high temperature, failure to complete soldering within a short time could result in device failure. therefore, the following items should always be observed in order to minimize the thermal stress to which the devices are subjected. always preheat the device. the delta temperature between the preheat and soldering should be 100 c or less.* when preheating and soldering, the temperature of the leads and the case must not exceed the maximum temperature ratings as shown on the data sheet. when using infrared heating with the reflow soldering method, the difference shall be a maximum of 10 c. the soldering temperature and time shall not exceed 260 c for more than 10 seconds. when shifting from preheating to soldering, the maximum temperature gradient shall be 5 c or less. after soldering has been completed, the device should be allowed to cool naturally for at least three minutes. gradual cooling should be used as the use of forced cooling will increase the temperature gradient and result in latent failure due to mechanical stress. mechanical stress or shock should not be applied during cooling. *soldering a device without preheating can cause excessive thermal shock and stress which can result in damage to the device.
ncp345 http://onsemi.com 8 package dimensions notes: 1. dimensioning and tolerancing per ansi y14.5m, 1982. 2. controlling dimension: millimeter. 3. maximum lead thickness includes lead finish thickness. minimum lead thickness is the minimum thickness of base material. dim min max min max inches millimeters a 2.90 3.10 0.1142 0.1220 b 1.30 1.70 0.0512 0.0669 c 0.90 1.10 0.0354 0.0433 d 0.25 0.50 0.0098 0.0197 g 0.85 1.00 0.0335 0.0413 h 0.013 0.100 0.0005 0.0040 j 0.10 0.26 0.0040 0.0102 k 0.20 0.60 0.0079 0.0236 l 1.25 1.55 0.0493 0.0610 m 0 10 0 10 s 2.50 3.00 0.0985 0.1181 0.05 (0.002) 123 54 s a g l b d h c k m j thin sot235 sn suffix plastic package case 48301 issue a on semiconductor and are trademarks of semiconductor components industries, llc (scillc). scillc reserves the right to make changes without further notice to any products herein. scillc makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does scillc assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. atypicalo parameters which may be provided in scill c data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including atypicalso must be validated for each customer application by customer's technical experts. scillc does not convey any license under its patent rights nor the rights of others. scillc products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body , or other applications intended to support or sustain life, or for any other application in which the failure of the scillc product could create a sit uation where personal injury or death may occur. should buyer purchase or use scillc products for any such unintended or unauthorized application, buyer shall indemnify and hold scillc and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthori zed use, even if such claim alleges that scillc was negligent regarding the design or manufacture of the part. scillc is an equal opportunity/affirmative action employer. publication ordering information japan : on semiconductor, japan customer focus center 4321 nishigotanda, shinagawaku, tokyo, japan 1410031 phone : 81357402700 email : r14525@onsemi.com on semiconductor website : http://onsemi.com for additional information, please contact your local sales representative. ncp345/d literature fulfillment : literature distribution center for on semiconductor p.o. box 5163, denver, colorado 80217 usa phone : 3036752175 or 8003443860 toll free usa/canada fax : 3036752176 or 8003443867 toll free usa/canada email : onlit@hibbertco.com n. american technical support : 8002829855 toll free usa/canada
|
