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this is preliminary information on a new product now in development or undergoing evaluation. details are subject to change without notice. august 2014 docid026509 rev 1 1/30 STFC01 integrated current limiter datasheet - preliminary data features ? wide range of supply voltage: from 10 to 52 v dc (can be extended above 120 v with external components) ? very low dc current: typ.1.5 ma ? external current limitation setting ? 3 modes of operation ? retriggerable ? foldback ?latched ? configurable trip-off and recovery times ? smart current limitation for repetitive overload ? embedded current sense ? configurable undervoltage protection ? floating ground description the STFC01 is an integrated current limiter designed to work with an external p-channel power mosfet. it can be used as a universal solution to protect a power supply (from 10 v) from anomalous external current demands (for example, if the load is in latch-up condition). it can protect or replace conventional fuses and can also be used to control loads. the STFC01 features 3 user-configurable operating modes (retriggerable, latch, foldback), with different behaviors in case of overload/short- circuit events. all key parameters of the application, including the current limit, the trip-off, recovery times and the undervoltage protection, are user- configurable, making the STFC01 suitable for a wide range of applications. because of its floating ground, it can even be used on power buses with voltage above its maximum specification 52 v supply voltage. the status and control pins allow the remote control of the device and the load. 62 www.st.com
contents STFC01 2/30 docid026509 rev 1 contents 1 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 typical application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 device description and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1 supply voltage, startup and undervoltage lockout . . . . . . . . . . . . . . . . . . 10 6.2 modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2.1 latched mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.2.2 retriggerable mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.2.3 foldback mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.3 current sense/limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.3.1 repetitive overload events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.4 gate driving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.5 telecommand interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.6 floating ground configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.7 status telemetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.8 analog current sense telemetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7 application guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.1 guidelines for operation at high voltage . . . . . . . . . . . . . . . . . . . . . . . . . . 23 8 layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 10 ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 11 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
docid026509 rev 1 3/30 STFC01 block diagram 30 1 block diagram figure 1. block diagram p ower supply sec tion (pre - reg, referenc e, bias ) status telemetry analog telemetry uvlo telecommand interfac e op-amp sens e c ore logic trip - off circ uitry vcc vcc vd comp vg tms- is ns - is ns + tms+ hys uvlo tc_on tc_off set_flb set_sts i_r e f ton toff gnd sts tm v cc c urrent l im and driver am17114v1
pin configuration STFC01 4/30 docid026509 rev 1 2 pin configuration figure 2. pin connections (top view) table 1. pin description pin name type description 1 set_sts digital input configuration pin. if shorted to gnd, the current limiter at power-up is off. if connected to v cc , the current limiter at power-up is normally on. 2 tc_off digital input telecommand interface input for off pulsed signal. 3 set_flb digital input configuration pin. if connected to v cc , the foldback mode is enabled. 4 ton analog output used to set the trip-off time t on . a c on capacitor is connected between this pin and gnd. 5 toff analog output used to set t off recovery time. this pin has a double functionality. if c off capacitor is connected between this pin and gnd, it sets the t off value in retriggerable mode. if the pin is shorted to gnd, the device is configured in latched mode. 6i_ref analog input/output used to set the current reference. an external high precision resistor is connected between this pin and gnd in order to set the current reference. 7 gnd power supply ground. return of the bias current and zero voltage reference for all internal voltages. connected to the main bus ground through a decoupling resistor to operate in floating ground configuration. *,3*59
docid026509 rev 1 5/30 STFC01 pin configuration 30 8 vd analog input sense pin of the external mosfet drain voltage used to detect current limitation. a small series resistor can be useful to reduce power dissipation. 9 sts digital output telemetry digital status. a resistor has to be connected between the pin and the main bus ground. 10 tms+ analog input non-inverting input of the telemetry circuit. an accurate external resistor is connected between isns+ and this pin to guarantee the requested accuracy on the output source current for the analog telemetry. 11 tms- analog input inverting input of the telemetry circuit. an accurate external resistor is connected between isns and this pin to guarantee the requested accuracy on the output source current for the analog telemetry. 12 tm analog output output source current for the analog telemetry. a resistor has to be connected between this pin and the main bus ground. 13 comp analog output output pin for current limitation loop compensation. 14 v g analog output mosfet gate driver output. 15 isns- analog input inverting input of the op-amp current limitation loop. the pin is tied directly to the hot (negative) end of the external current sense resistor. 16 isns+ analog input non-inverting input of the op-amp current limitation loop. the pin is tied directly to the hot (positive) end of the external current sense resistor. 17 v cc power supply supply input voltage. 18 hys analog output external setting of the uvlo hysteresis. a resistor has to be connected between the main bus and this pin. 19 tc_on digital input telecommand interface input for on pulsed signal. 20 uvlo analog input external setting of the uvlo turn-on threshold. the pin has to be tied to the midpoint of a resistor divider sensing the supply voltage vs. main bus ground. table 1. pin description (continued) pin name type description
typical application diagram STFC01 6/30 docid026509 rev 1 3 typical application diagram figure 3. typical application circuit note: r gnd , r sts and r tm resistors are very important for the application safety. please refer to section 7: application guidelines for their implementation. am1711 STFC01 bus supply bus ground hys uvlo tc_on tc_off on off o n o f f f f telecommand interface tms+ isns+ isns - tms- vg comp vd i_ref ton toff gnd sts tm sts tm set_sts set_flb s t s t m telemetry power section setting section undervoltage lockout r sense r tm r sts pw 1 r h r 1 r 2 vcc r tms r tms r ir c on c off r gnd c vcc r comp c comp load 3.3 k 22 nf
docid026509 rev 1 7/30 STFC01 maximum ratings 30 4 maximum ratings note: absolute maximum ratings are those values beyond which damage to the device may occur. functional operation under these conditions is not implied. table 2. absolute maximum ratings symbol parameter value unit t stg storage temperature -65 to 150 c t j maximum junction temperature 150 c v hbm esd capability, human body model 2 k v set_sts digital input -0.3 to (v cc + 0.3) v tc_off digital input -32.6 to (v cc + 0.3) v set_flb digital input -0.3 to (v cc + 0.3) v ton analog output -0.3 to + 4.6 v toff analog output -0.3 to + 4.6 v i_ref analog input/output -0.3 to + 4.6 v gnd device ground - vd analog input -32.6 to (v cc + 0.3) v sts digital output -32.6 to (v cc + 0.3) v tms+ analog input -0.3 to (v cc + 0.3) v tms- analog input -0.3 to (v cc + 0.3) v tm analog output -32.6 to (v cc + 0.3) v comp analog output -0.3 to (v cc + 0.3) v v g analog output -0.3 to (v cc + 0.3) v isns- analog input -0.3 to (v cc + 0.3) v isns+ analog input -0.3 to (v cc + 0.3) v v cc power supply -0.3 to + 54.0 v hys analog output -0.3 to (v cc + 0.3) v tc_on digital input -32.6 to (v cc + 0.3) v uvlo analog input -0.3 to (v cc + 0.3) v table 3. thermal data symbol parameter value unit r thjc thermal resistance junction-case 40 c/w r tj-a thermal resistance junction-case 40 c/w
electrical characteristics STFC01 8/30 docid026509 rev 1 5 electrical characteristics t j = - 40 c to 125 c, v cc = 37 v, unless otherwise specified. table 4. electrical characteristics symbol parameter test conditions min. typ. max. unit v cc system operating supply voltage 10 52 v supply current and uvlo v z v cc vs. gnd internal clamp voltage 18.0 19.6 21.2 v i cc on supply current, on-state v cc - gnd < v z 1.5 3 ma i cc off supply current, off-state v cc - gnd < v z 1.5 3 ma v th undervoltage lockout turn-on threshold ( 2 ) r1 = 20 k ? , r2 = 220 k ? , rh = 1.6 k ? 28 30 32 v undervoltage lockout hysteresis ( 2 ) 1.8 2 2.2 v current limitation i lim current limitation sense voltage threshold (between isns+ and isns-) 90 100 110 mv driver v g on gate voltage range, on-state v cc - 12 v v g off gate voltage range, off-state v cc i g gate source current set_sts low v g = v cc - 1 v 20 ma gate sink current set_sts high v g = v cc - 9 v -20 ma trip-off function t on trip-off time r i_ref = 120 k ? c on = 10 nf 1.2 ms t off recovery time r i_ref = 120 k ? c on = 10 nf c off = 47 nf 112 switching times t delay delay time (from tc_on to v out = 0 to 10%) latched-off configuration (see table 8 ) 29 ms t rise rise time (v out from 10% to 90%) 40 t fall fall time (v out from 90% to 10%) 30 t storage storage time (from tc_off to v out = 10%) 47
docid026509 rev 1 9/30 STFC01 electrical characteristics 30 note: the operating range of current limitation and load depends on the current capability of the power mosfet. this range can be extended to higher values according to the current capability of the power mosfet. undervoltage lockout threshold calculation (see figure 3 ): v on = v th = 2.5 v * ((r 1 +r 2 ) / r 1 ); v off = 2.5 v * ((r 1 + r 2 + r h ) / (r 1 + r h )); v hy = v th - v off mgnd is the main bus ground voltage. telecommand v tc_on/tc_off telecommand input voltage turn-on/off 2 2.8 3.6 v t pulse telecommand minimum pulse time 30 100 s t pulse_noise telecommand immunity pulse time 10 s telemetry v tm telemetry output voltage range r sense = 100 m ? r tms = 5 k ? r tm = 240 k ? i sense = 500 ma 2.4 v v tm(off) telemetry output voltage range, off-state r sense = 100 m ? r tms = 5 k ? r tm = 240 k ? i sense = 0 ma mgnd v status v status sts output voltage range r sts = 50 k ? 5v v status(off) sts output voltage range, off-state mgnd table 4. electrical characteristics (continued) symbol parameter test conditions min. typ. max. unit
device description and operation STFC01 10/30 docid026509 rev 1 6 device description and operation the STFC01 (integrated current limiter) is a versatile monolithic device used as a high-side gate driver or intelligent power switch driver, to give current limitation and protect the main bus in case of excessive current demands. the device can operate with a supply voltage range from 10 v to 52 v. an undervoltage lockout circuitry guarantees the appropriate power supply integrity. because of the wide spectrum of load voltage that can be requested, this device can be configured to protect a broad variety of loads. in case of overload, the device behavior changes according to its configured mode of operation: ? if the current limiter is configured in retriggerable mode, after the trip-off time, the device switches off and remains in this state for a recovery time that is externally programmable. once this time elapses, the device switches cyclically on and off again while the overload persists. ? if configured in foldback mode, in case of overload, the device provides current limitation, with a value decreasing with the output voltage, reaching a fixed and safe value even if a short-circuit persists. ? if configured in latched mode, the device has the current limitation feature for an externally configurable time, called trip-off time, and if the overcurrent condition exceeds this time, the device switches off. in this case, the device may be switched on again, through the telecommand pin only. the core of the device consists of the driver block, designed to drive an external p-channel power mosfet connected as high-side configuration. current sensing, current limitation detection, remote control, telemetry and protection functions are also included allowing the design of high reliability systems. thanks to the remote monitor and telecommand interface features, the STFC01 performs the full control and the partitioning of each load connected to the device. 6.1 supply voltage, startup and undervoltage lockout the device can be directly supplied with a voltage range from 10 v to 52 v. a zener diode chain is embedded to clamp the voltage level between v cc and gnd at 20 v (typ. 19.6 v). the device can be configured to power up either in off or on-state, depending on the configuration of set_sts pin. if the device is configured on at power-up (set_sts pin is connected to v cc ), when the supply bus reaches the turn-on threshold, the device is ready to drive the mosfet. there is no point in receiving the on command by the telecommand interface to enable the device. table 5. power-up settings set_sts mode gnd off @ power-up v cc on @ power-up
docid026509 rev 1 11/30 STFC01 device description and operation 30 if the device is configured off at power-up (set_sts pin is connected to gnd), when the supply bus reaches the turn-on threshold, the device waits for the on command on the telecommand interface to switch on. the uvlo circuit protects the device from an incorrect bias condition. the setting of the disconnection and reconnection thresholds (turn-off and turn-on) is performed by r h -r 1 -r 2 external resistor divider connected between v cc and the main bus ground (mgnd). the connection point between r 1 and r 2 is tied to the ulvo pin ( figure 3 ). hysteresis is implemented to avoid undesired oscillations caused by bus voltage transients. the hysteresis value can be set through the connection of the resistor r h between v cc and hys pin ( figure 3 ). r 1 , r 2 and r h can be chosen using the following equations: equation 1 equation 2 equation 3 where: ?v on is the undervoltage lockout turn-on threshold ?v off is the undervoltage lockout turn-off threshold ?v hys is the undervoltage lockout hysteresis in equation 1 , v on is obtained assuming that r h is greater than the drain-to-source on resistor of the internal switch connected between hys and v cc pads (switch embedded in the device used to short the r h resistor and whose on-resistance acts in parallel to r h ). the value of this resistor is about 160 . an internal masking time ignores bus undervoltage events lower than 50 s. this allows the device to be protected from the turn-off in case of glitches or transient noise occurring on the main supply bus. if a masking time value, higher than 50 s, is needed, an external capacitor can be connected between the main supply bus and uvlo pin. once uvlo event is triggered and recovered, the device restarts according to the configuration defined by set_sts pin. v on 2.5 r 1 r 2 + r 1 ------------------- - ? = v off 2.5 r 1 r 2 r h ++ r 1 r h + ---------------------------------- ? = v hys v on v off ? =
device description and operation STFC01 12/30 docid026509 rev 1 6.2 modes of operation when an overcurrent event occurs, the device detects this condition and the trip-off timer starts. the device drives the external mosfet to limit the current across the load (current limitation mode) and if the overcurrent condition lasts more than t on trip-off time, at the end of t on period, the external mosfet turns off. instead, if the overcurrent event lasts for an interval shorter than t on , the device limits the current for the duration of the fault and recovers as soon as the overcurrent condition disappears (mosfet is driven to its low- ohmic status with the channel well-saturated). t on trip-off time can be set through c on external capacitor connected between t on and gnd pin, as shown in the application diagram ( figure 3 ). c on capacitor is charged with i ref constant current whose value is externally set by r ir resistor connected between i_ref and gnd pins, so that t on trip-off time value is defined by the following equation. equation 4 t on = c on * r ir c on capacitor charging phase starts as soon as the overcurrent event is detected by i ref constant current value, externally set by r ir resistor connected between i_ref and gnd pin. at the end of a current limitation period (either t on time has elapsed and the mosfet is switched off or the overcurrent event has disappeared), the discharging phase of the c on capacitor starts with a current which is 20 times smaller than the charging phase. with this high charge/discharge ratio, if the overcurrent event occurs frequently and each time for a shorter period than t on trip-off time, the mosfet turns off (after a number of overcurrent events). in this manner, the device implements a sort of memory of overcurrent events whose single duration is shorter than t on , thus avoiding dangerous thermal stress to the mosfet (hiccup mode). the procedure can be latched or retriggerable and depends on how toff pin is connected. table 6. toff pin settings toff mode gnd latched c off retriggerable
docid026509 rev 1 13/30 STFC01 device description and operation 30 6.2.1 latched mode the device is configured as a latched current limiter (see figure 4 ) when toff pin is shorted directly to gnd. in this mode, if the duration of the overcurrent event is longer than trip-off time, the external mosfet latches off and remains off until the reset is given by either the telecommand interface or uvlo activation/deactivation cycle. when the device is configured as a latched current limiter, the use of the telecommand interface is required. moreover, if this configuration mode is set, the start-up mode of the device can be selected between latched-off (the device is off at power-up) and latched-on (the device is on at power-up) using set_sts pin. figure 4 refers to latched-off start-up mode selection. figure 4. typical application diagram with the STFC01 configured as latched current limiter, latched-off at startup note: r gnd , r sts and r tm resistors are very important for the safety of the application. please refer to section 7: application guidelines for their implementation. am17116v1 STFC01 hys uvlo tc_on tc_off on off tms+ isns+ isns - tms - vg comp vd i_ref ton toff gnd sts tm sts tm set_sts set_slb vcc latched configuration load bus supply bus ground
device description and operation STFC01 14/30 docid026509 rev 1 6.2.2 retriggerable mode the device is configured as a retriggerable current limiter (see figure 5 ) when c off external capacitor is connected between toff pin and gnd. in retriggerable mode, if the duration of the overcurrent is longer than t on trip-off time, the external mosfet is switched off (as when the latched mode is selected) but the mosfet stays off during the recovery time t off . when t off time elapses, the device restarts autonomously to its normal condition, turning on again the mosfet. t on trip-off time, as well as t off recovery time, can be externally set through c off external capacitor connected between toff and gnd pin, as shown in the application diagram with the STFC01 configured as a retriggerable current limiter ( figure 5 ). c off capacitor is charged with a constant current whose value is a fraction (1/20) of i ref (externally set by r ir resistor connected between i_ref and gnd pin). c off capacitor charging phase starts as soon as t on time has elapsed, therefore t off time is equal to c off charging time defined by: equation 5 t off = 20 * r ir * c off for safety reasons, c off capacitor is quickly discharged. t off is generated not only after a current limitation event whose duration is longer than t on time, but also after any event that turns off the device. when the device is configured as a retriggerable current limiter, the following settings are recommended: ? to select the option on at power-up, connecting set_sts pin to v cc ? to disable the telecommand interface, connecting tc_on and tc_off pins to v cc figure 5. typical application diagram with the STFC01 configured as retriggerable current limiter note: r gnd , r sts and r tm resistors are very important for the safety of the application. please refer to section 7: application guidelines for their implementation. am17117v1 STFC01 hys uvlo tc_on tc_off tms+ isns+ isns - tms - vg comp vd i_ref ton toff gnd sts tm sts tm set_sts set_flb vcc retriggerable configuration load bus supply bus ground
docid026509 rev 1 15/30 STFC01 device description and operation 30 6.2.3 foldback mode the device can be configured as a foldback current limiter through set_flb configuration pin (see figure 6 ). a foldback current limiter is a special device that never turns off, otherwise the application could be compromised. when an overcurrent event is detected, the device implements the current limitation feature whose value depends on the output voltage, reaching a small and safe value even if a short-circuit on the load occurs and remains. if the foldback mode is selected: ? select the option on at power-up, connecting set_sts pin to v cc ? disable trip-off function, connecting ton and toff pin to gnd ? disable the telecommand interface, connecting tc_on and tc_off pin to v cc when configured as a foldback current limiter, additional resistors have to be connected between vd and isns- pin and each end of r sense resistor, isns- and isns+ (see figure 6 ). figure 6. typical applicati on diagram with the STFC01 configured as a foldback current limiter note: r gnd , r sts and r tm resistors are very important for the safety of the application. please refer to section 7: application guidelines for their implementation. the device can be configured in different modes using suitable combinations of the configuration pins quoted in the table below. table 7. foldback mode setting set_flb mode gnd foldback mode disabled v cc foldback mode enabled am17118v1 STFC01 hys uvlo tc_on tc_off tms+ isns+ isns - tms - vg comp vd i_ref ton toff gnd sts tm sts tm set_sts set_flb vcc foldback configuration load r r r flb bus supply bus ground
device description and operation STFC01 16/30 docid026509 rev 1 6.3 current sense/limitation the voltage drop on the external r sense resistor (see figure 3 ) is continuously monitored (by isns+ and isns- pins) and compared with a fixed 100 mv internally generated threshold. if the voltage drop on r sense surpasses 100 mv, the current demand becomes excessive and the timer counts the trip-off time t on and the device enters the current limitation mode. in this condition, the limitation control loop is enabled to force v g to the proper voltage level, limiting the current to the load. rc compensation network could be connected between v g and comp pin to improve the loop stability. the current limitation threshold can be externally set according to the application requirements by r sense resistor. when configured as either retriggerable or latched current limiter, it is: equation 6 where i lim is the limitation current, r sense resistor can be chosen by: equation 7 if configured as a foldback current limiter (see figure 6 ), it is: equation 8 table 8. device configuration truth table configuration set_flb set_sts tc_on tc_off ton toff status at power-up latched-off 0 0 telecommand telecommand c on gnd off @ power-up latched-on 0 1 telecommand telecommand c on gnd on @ power-up retriggerable 01 v cc v cc c on c off on @ power-up foldback 11 v cc v cc gnd gnd on @ power-up i lim 100mv r sense ? = r sense 100mv 100i lim ? = i lim 100mv r r flb ------------ - v cc v d ? () ? r sense -------------------------------------------------------------------- - =
docid026509 rev 1 17/30 STFC01 device description and operation 30 6.3.1 repetitive overload events in case of repetitive overload events each one, having a duration t < t on , a ?memory? of the previous current limitation events, keeps the junction temperature of the external mosfet at safety level. this function, working both in latched and retriggerable modes, is depicted in the following figures. figure 7. behavior under repetitive overloads figure 8. behavior under repetitive overloads (magnification) am17119v1 i out (internal signal) v con v drain (internal signal) v cur_lim am17120v1 (internal signal) v con i out v drain v pulse
device description and operation STFC01 18/30 docid026509 rev 1 6.4 gate driving the driver circuit is designed to drive an external p-channel power mosfet (connected in high-side configuration) providing on v g pin a voltage signal in the range from v cc to v cc - 12 v. when the device works in normal operating mode (which means the device is neither off nor in current limitation mode) v g node is pulled down and the gate of the external mosfet is internally clamped about 12 v below the supply voltage v cc making the channel of the mosfet well-saturated. ? when the mosfet has to be switched off, v g goes up to v cc ? when the mosfet is in current limitation mode, v g voltage is defined by the limitation control loop 6.5 telecommand interface the STFC01 can be enabled or disabled by two digital signals through tc_on and tc_off pins. if the voltage on tc_on pin is forced low for a typical pulse time of 100 s, the device switches on. in the same way, a low voltage for a typical pulse time of 100 s forced on tc_off pin switches off the device. to have a more robust implementation, unwanted on/off pulses, having a short duration (shorter than 10 s), are ignored to have a sort of noise immunity of the telecommand system. in case of contemporaneous application of on and off commands, off command has the priority, which means that in case of a failure of the telecommand interface resulting in a permanent on-state, the device can be switched off by sending the off command. 6.6 floating ground configuration as mentioned in section 6.1 , a zener diode chain is embedded to clamp the voltage level between v cc and gnd at about v z = 20 v (typ. 19.6 v). if the operating supply bus is v cc < v z , the zener clamp is off and the total current consumption of the device is about 1.5 ma @ v cc ~ 19.4 v, near the on threshold for the clamp. if the operating supply bus is v cc > v z , the zener clamp is on and the current consumption of this zener diode chain is added to the previous current consumption of the device. in order to benefit from the floating ground feature and therefore to improve the device performance in terms of power line rejection, the device should operate with the zener clamp active. a good trade-off is to establish a total current consumption of 2 ma, therefore the floating ground resistor is sized according to the following resistor. equation 9 where: r gnd v cc v z ? i cc -------------------- - =
docid026509 rev 1 19/30 STFC01 device description and operation 30 v cc = system operating supply voltage v z = v cc vs. gnd internal clamp voltage i cc = supply current whose recommend value is 2 ma the implementation of the floating ground feature is useful to avoid the collapse of the bus supply vs. the bus ground, compromising the application as a result of a possible short of the supply line vs. ground inside the device. in case of a short-circuit inside the device, the external r gnd resistor ( figure 3 ) connected between gnd pin and the main bus ground has to sustain the overall voltage between the bus supply and ground. the power dissipation of this resistor has to be sized properly to dissipate the power according to the steady-state value of the supply bus. additional single point failure protection recommendations can be found in section 7: application guidelines . 6.7 status telemetry the status telemetry circuit gives information about the device status. this information can be retrieved by monitoring sts output pin. when on command is received through tc_on pin or the device turns on because of the undervoltage event to a normal operation mode, sts output is forced high. sts output is forced low when one of the following events occurs. ? the device turns off the external mosfet as a consequence of a current limitation event ? off command is received through tc_off pin to turn off the device ? off command is received through tc_off pin to reset a latch condition sts is an open drain pin, which is able to source a 100 a fixed current, so that an external resistor r sts ( figure 3 ) has to be connected between sts pin and the main bus ground. r sts value has to be chosen according to the desired high voltage level (v h_sts ) as per below equation. equation 10 6.8 analog current sense telemetry the telemetry circuit gives some information about the current across the load. this circuit provides on tm pin a source current whose value is proportional to the current flowing from the bus supply line to the load. the voltage drop on r tm external resistor ( figure 3 ), table 9. telemetry digital status pin sts mode low device is in off-state high device is in on-state r sts v h sts ? 100 ? () ? =
device description and operation STFC01 20/30 docid026509 rev 1 connected between tm pin and the main bus ground, is proportional to the current load, performing a current/voltage conversion. this function is implemented by sensing the voltage drop on the external r sense resistor through r tms resistor connected to tms+ and tms- pin. equation 11 equation 12 where v tm is the voltage drop on r tm external resistor that has to be monitored to have information on the corresponding i rsense current. i rtm i rsense r sense r tms -------------------- ? = r tm v tm i rtm ----------- - v tm i sense ----------------- - r tms r sense -------------------- ? ==
docid026509 rev 1 21/30 STFC01 application guidelines 30 7 application guidelines in a floating ground configuration, the application can be protected from single point failures of the resistor connected between gnd and the gnd bus (r gnd ), and the telemetry resistors (r sts and r tm ). in fact, in case of failure of these resistors, damage may occur to the device itself and to the other devices connected to the same bus. the figure below shows a typical implementation of the protection described above, with additional components named: r gnd_1 , r gnd_2 , d status , r status2 , d fw , d tm.
application guidelines STFC01 22/30 docid026509 rev 1 figure 9. recommended typical application schematic with single failure protection STFC01 retriggerable with single failure free (2 nd solution) supply bus r sense r 1 r 0 r hys r g r status1 r tm1 c g r f c f bus gnd to load d fw uvlo hys t_on t_off set_status tc_off vcc isns+ tms+ vout/vg tm status gnd tc_on isns - tms - fcl_cfg vd on off i_ref comp r iref telecommand interface core logic uvlo power supply section (pre-regulator, reference, bias) status telemetry op-amp sense telemetry vcc trip-off circuitry driver vcc r gnd_2 c tm d tm c status d status r tm2 r status2 r vd c vd telecommand interface r gnd_1 gipg1106141019lm
docid026509 rev 1 23/30 STFC01 application guidelines 30 7.1 guidelines for operation at high voltage the device withstands up to 52 v between bus_supply and bus_gnd. nevertheless it is possible, by adding external components, to work at a bus supply higher than 52 v, as described in the following figure.
application guidelines STFC01 24/30 docid026509 rev 1 figure 10. schematic for operation at bus voltages higher than 52 v supply bus r sense r 1 r 0 r hys r g r fgnd_1 c g r f c f bus gnd to harness and load/user d fw uvlo hys t_on t_off set_status tc_off vcc isns+ tms+ vout/vg tm status gnd tc_on isns - tms - fcl_cfg vd on off tele command interface i_ref comp r iref core logic uvlo power supply section (pre-regulator, reference, bias) status telemetry op-amp sense telemetry vcc trip-off circuitry driver vcc r fgnd_2 gnd gnd STFC01 @ 100 v with single failure free (2^ solution) d tc_off tr status tr tm d vcc_vd r status1 r tm1 c tm d tm c status d status r tm2 r status2 telecommand interface r tc_off d tc_on r tc_on gipg1106141143lm
docid026509 rev 1 25/30 STFC01 application guidelines 30 r tc_on and r tc_off resistors in series to pull-down transistors of the telecommand circuitry are sized to guarantee that pins never go to - 32 v under gnd, the substrate reference of the device. d tc_on and d tc_off diodes are connected in series to pull-down transistors. telemetry pins (tm and status) are connected to bus gnd through the external hv p- ch transistors (tr status , tr tm ) used in cascade configuration, with gate connected to gnd. d status , d tm diodes and r tm2 and r status2 resistors are also connected. v d pin is clamped (for example through a zener diode among v cc , v d and d vcc_vd ) in order to avoid this pin to go to -32 v under gnd when the device is in off-state or in case of a short-circuit. d fw diode is connected between supply bus and ground.
layout guidelines STFC01 26/30 docid026509 rev 1 8 layout guidelines the STFC01 simultaneously handles fast switching and medium voltage, which implies specific attention to the layout. the first priority when components are placed is the power section (current path from input, through current sense resistor and high-side switch, toward output), minimizing the length of each connection and loop at the maximum. besides, the path of the gate driver signal (driving on/off the high-side switch) has to present the lowest resistance. a power resistor might be required in series to this path to protect the integrated gate driver. to minimize noise and voltage spikes (emi and losses), power connections have to be a part of a power plane and implemented using wide and thick conductor traces. the loop has to be minimized. the inductance effect, leading to ringing of tracks can be minimized by making tracks as short as possible. the number of vias must be minimized to reduce the related parasitic effect. a capacitor on v cc , as well as the capacitors connected to the digital pins, should be placed as closer as possible to ic to reduce the possible loop and parasitic inductance. small signal components and connections to critical nodes (tc_on/off, isns+ and isns) of the application are also important. in fact, the symmetry of the path may impact the sampled value. finally, for reliability reasons, more than one resistor should be used (series connected) between the device and the main bus ground whose total value is obtained by application design considerations.
docid026509 rev 1 27/30 STFC01 package mechanical data 30 9 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. figure 11. so-20 drawings $ h % ' ( / . + $ & 620(& k[?
package mechanical data STFC01 28/30 docid026509 rev 1 table 10. so-20 mechanical data dim. mm min. typ. max. a2.35 2.65 a1 0.1 0.3 b0.33 0.51 c0.23 0.32 d12.6 13 e7.4 7.6 e1.27 h10 10.65 h0.25 0.75 i 0.4 1.27
docid026509 rev 1 29/30 STFC01 ordering information 30 10 ordering information 11 revision history table 11. ordering information order code package marking STFC01dr so-20 STFC01d table 12. document revision history date revision changes 07-aug-2014 1 initial release.
STFC01 30/30 docid026509 rev 1 important notice ? please read carefully stmicroelectronics nv and its subsidiaries (?st?) reserve the right to make changes, corrections, enhancements, modifications, and improvements to st products and/or to this document at any time without notice. purchasers should obtain the latest relevant in formation on st products before placing orders. st products are sold pursuant to st?s terms and conditions of sale in place at the time of o rder acknowledgement. purchasers are solely responsible for the choice, selection, and use of st products and st assumes no liability for application assistance or the design of purchasers? products. no license, express or implied, to any intellectual property right is granted by st herein. resale of st products with provisions different from the information set forth herein shall void any warranty granted by st for such product. st and the st logo are trademarks of st. all other product or service names are the property of their respective owners. information in this document supersedes and replaces information previously supplied in any prior versions of this document. ? 2014 stmicroelectronics ? all rights reserved

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