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rt9702/a 1 ds9702/a-15 april 2011 www.richtek.com 80m , 500ma/1.1a high side power switches with flag marking information for marking information, contact our sales representative directly or through a richtek distributor located in your area. ordering information general description the rt9702 and RT9702A are cost-effective, low voltage, single n-channel mosfet high-side power switches, optimized for self-powered and bus- powered universal serial bus (usb) applications. the rt9702/a equipped with a charge pump circuitry to drive the internal mosfet switch; the switch's low r ds(on) , 80m , meets usb voltage drop requirements; and a flag output is available to indicate fault conditions to the local usb controller. additional features include soft-start to limit inrush current during plug-in, thermal shutdown to prevent catastrophic switch failure from high current loads, under-voltage lockout (uvlo) to ensure that the device remains off unless there is a valid input voltage present, fault current is limited to typically 800ma for rt9702 in single port and 1.5a for RT9702A in dual ports in accordance with the usb power requirements, lower quiescent current as 25 a making this device ideal for portable battery-operated equipment. the rt9702/a is available in sot-23-5 and tsot-23-5 packages requiring minimum board space and smallest components. features z z z z z compliant to usb specifications z z z z z built-in (typically 80m ) n-channel mosfet z z z z z output can be forced higher than input (off-state) z z z z z low supply current : 25ua typical at switch on state 1ua typical at switch off state z z z z z guaranteed 500ma/rt9702 and 1.1a/RT9702A continuous load current z z z z z wide input voltage ranges : 2v to 5.5v z z z z z open-drain fault flag output z z z z z hot plug-in application (soft-start) z z z z z 1.7v typical under voltage lockout (uvlo) z z z z z current limiting protection z z z z z thermal shutdown protection z z z z z reverse current flow blocking (no body diode) z z z z z smallest sot-23-5 a nd tsot-23-5 packages minimizes board space z z z z z ul approved ? ? ? ? ? e219878 z z z z z tuv iec60950-1 : 2005 certified z z z z z rohs compliant and 100% lead (pb)-free applications z usb bus/self powered hubs z usb peripherals z acpi power distribution z pc card hot swap z notebook, motherboard pcs z battery-powered equipment z hot-plug power supplies z battery-charger circuits note : richtek products are : ` rohs compliant and compatible with the current require- ments of ipc/jedec j-std-020. ` suitable for use in snpb or pb-free soldering processes. rt9702/a package type b : sot-23-5 j5 : tsot-23-5 lead plating system p : pb free g : green (halogen free and pb free) 1.1a output current 500ma output current
rt9702/a 2 ds9702/a-15 april 2011 www.richtek.com function block diagram functional pin description pin name pin function vin power input voltage vout output voltage gnd ground en chip enable (active high) flg open-drain fault flag output gate control output voltage detection delay oscillator uvlo charge pump bias thermal protection current limiting flg vout vin en gnd typical application circuit note: a low-esr 150 f aluminum electrolytic or tantalum between v out and gnd is strongly recommended to meet the 330mv maximum droop requirement in the hub v bus . (see application information section for further details) pin configurations (top view) sot-23-5/tsot-23-5 en gnd vout vin 4 23 5 flg vin en flg vout gnd rt9702/a + over -current v bus d+ d- gnd 0.1f 10k usb controller 1f 150f 10f supply voltage 5v pull-up resistor (10k to 100k) (optional) flag transient filtering) ferrite beades data chip enable
rt9702/a 3 ds9702/a-15 april 2011 www.richtek.com test circuits 12 34 5 vin en flg vout gnd rt9702/a + + r l a i out s3 c out i l v out r fg c in v in s2 v flg vin en flg vout gnd rt9702/a + + r l c out i l v out r fg c in v in v ce v flg vin en flg vout gnd rt9702/a + + r l a i out s1 c out i l v out r fg c in v in v flg chip enable vin en flg vout gnd rt9702/a + r l a i supply c in v in a i leak age v flg chip enable vin en flg vout gnd rt9702/a + + i out c out v rds(on) c in v in v chip enable note: above test circuits reflected the graphs shown on ? typical operating characteristics ? are as follows: ? turn-on rising & falling time vs. temperature, turn-on & off response, flag response ? supply current vs. input voltage & temperature, switch off supply current vs. temperature, turn-off leakage current vs. temperature ? on-resistance vs. input voltage & temperature ? en threshold voltage vs. input voltage & temperature, flag delay time vs. input voltage & temperature, uvlo threshold vs. temperature, uvlo at rising & falling ? current limit vs. input voltage/temperature, short circuit current response, short circuit current vs. temperature, inrush current response, soft-start response, ramped load response, current limit transient response, thermal shutdown response 1 2 3 4 5
rt9702/a 4 ds9702/a-15 april 2011 www.richtek.com absolute maximum ratings (note 1) z supply voltage --------------------------------------------------------------------------------------------------------- 6.5v z chip enable input v oltage ------------------------------------------------------------------------------------------- ? 0.3v to 6.5v z flag voltage ------------------------------------------------------------------------------------------------------------ 6.5v z power dissipation, p d @ t a = 25 c sot-23-5, tsot-23-5 ------------------------------------------------------------------------------------------------- 0.4w z package thermal resistance (note 2) sot-23-5, tsot-23-5, ja ------------------------------------------------------------------------------------------- 250 c/w z junction temperature ------------------------------------------------------------------------------------------------- 150 c z lead temperature (soldering, 10 se c.) --------------------------------------------------------------------------- 260 c z storage temperature range ---------------------------------------------------------------------------------------- ? 65 c to 150 c z esd susceptibility (note 3) hbm (human body mode) ------------------------------------------------------------------------------------------ 8kv mm (ma chine mode) -------------------------------------------------------------------------------------------------- 800v electrical characteristics recommended operating conditions (note 4) z supply input voltage -------------------------------------------------------------------------------------------------- 2v to 5.5 v z chip enable input voltage ------------------------------------------------------------------------------------------- 0v to 5.5v z junction temperature range ---------------------------------------------------------------------------------------- ? 40 c to 125 c z ambient temperature range ---------------------------------------------------------------------------------------- ? 40 c to 85 c parameter symbol test conditions min typ max unit rt9702 i out = 500ma switch on resistance RT9702A r ds (o n) i out = 1.1a -- 80 100 m i sw_on switch on, v out = open -- 25 45 supply current i sw_off switch off, v out = open -- 0.1 1 a logic-low v il v in = 2v to 5.5v, switch off -- -- 0.8 v en threshold voltage logic-high v ih v in = 2v to 5.5v, switch on 2.0 -- -- v en input current i en v en = 0v to 5.5v -- 0.01 -- a output leakage current i leakage v en = 0v, r load = 0 -- 0.5 10 a output turn-on rise time t on_rise 10% to 90% of v out rising -- 400 -- s rt9702 0.5 0.8 1.1 current limit RT9702A i li m r load = 1 1.1 1.5 2.0 a rt9702 -- 0.8 -- short circuit fold- back current RT9702A i sc_fb v out = 0v, measured prior to thermal shutdown -- 1.0 -- a flag output resistance r flg i sink = 1ma -- 20 400 flag off current i flg_off v flg = 5v -- 0.01 1 a flag delay time (note 5) t d from fault condition to flg assertion 2 10 15 ms (v in = 5v, c in = c out = 1 f, t a = 25c, unless otherwise specified) to be continued
rt9702/a 5 ds9702/a-15 april 2011 www.richtek.com parameter symbol test conditions min typ max unit under voltage lockout v uv lo v in increasing 1.3 1.7 -- v under voltage hysteresis v uvlo v in decreasing -- 0.1 -- v thermal shutdown protection t sd -- 130 -- c thermal shutdown hysteresis t sd -- 20 -- c note 1. stresses listed as the above "absolute maximum ratings" may cause permanent damage to the device. these are for stress ratings. functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. note 2. ja is measured in the natural convection at t a = 25 c on a low effective thermal conductivity single layer test board of jedec 51-3 thermal measurement standard. note 3. devices are esd sensitive. handling precaution is recommended. note 4. the device is not guaranteed to function outside its operating conditions. note 5. the flag delay time is input voltage dependent, see ? typical operating characteristics ? graph for further details.
rt9702/a 6 ds9702/a-15 april 2011 www.richtek.com current limit vs. input voltage 1.0 1.2 1.4 1.6 1.8 2.0 2 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) current limit (a) on-resistance vs. input voltage 0 20 40 60 80 100 120 140 160 22.533.544.555.5 input voltage (v) on-resistance (m [ ) on-resistance vs. temperature 0 20 40 60 80 100 120 140 160 -40 -20 0 20 40 60 80 100 120 temperature (c) on-resistance (m ? ) supply current vs. temperature 0 5 10 15 20 25 30 35 40 -40 -20 0 20 40 60 80 100 120 temperature (c) supply current ( a) supply curent vs. input voltage 0 5 10 15 20 25 30 35 40 22.533.544.555.5 input voltage (v) supply current ( a) typical operating characteristics (u.u.t: RT9702Axb, unless otherwise indicated) v in = v en = 5v c in = 33 f r l = open 2 c in = c out = 33 f i out = 1.1a 3 2 v in = v en = 5v, r l = open c in = 33 f, c out = 33 f 3 v in = 5v c in = c out = 33 f i out = 1.1a current limit vs. input voltage 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 22.533.544.555.5 input voltage (v) current limit (a) c in = 33 f, c out = 33 f s2 = on, s3 = off , r l = 1 5 rt9702 c in = 33 f, c out = 33 f s2 = on, s3 = off , r l = 1 5 (m ) (m )
rt9702/a 7 ds9702/a-15 april 2011 www.richtek.com en threshold voltage vs. input voltage 0 0.4 0.8 1.2 1.6 2 2.4 2 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) en threshold voltage (v) en threshhold voltage vs. temperature 0 0.4 0.8 1.2 1.6 2 2.4 -40-20 0 20406080100120 temperature (c) en threshold voltage (v) turn-off falling time vs. temperature 0 20 40 60 80 100 120 140 -40 -20 0 20 40 60 80 100 120 temperature (c) turn-off falling time ( s) turn-on rising time vs. temperature 0 90 180 270 360 450 540 630 720 -40 -20 0 20 40 60 80 100 120 temperature (c) turn-on rising time ( s) short circuit current vs. temperature 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -40 -20 0 20 40 60 80 100 120 temperature (c) short circuit current (a) v in = 5v, r l = 30 c in = 33 f, c out = 1 f s1 = on 1 v in = 5v, r l = 30 c in = 33uf, c out = 1 f s1 = on 1 v in =5v, s2 = s3 = on c i n = 33 f c out = 0.1 f short circuit current response 0 5 0 1 2 v out (v) i out (a) 5 5 v in = 5v c i n = c out = 33 f s2 = s3 = on c in = c out = 33 f i l = 100ma 4 v in = 5v c in = c out = 33 f i l = 100ma 4
rt9702/a 8 ds9702/a-15 april 2011 www.richtek.com uvlo threshold vs. temperature 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -40 -20 0 20 40 60 80 100 120 temperature (c) uvlo threshold (v) flag delay time vs. temperature 7 8 9 10 11 12 13 14 15 16 -40 -20 0 20 40 60 80 100 120 temperature (c) delay time (ms) current limit vs. temperature 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 -40 -20 0 20 40 60 80 100 120 temperature (c) current limit (a) flag delay time vs. input voltage 0 4 8 12 16 20 24 22.533.544.555.5 input voltage (v) delay time (ms) turn-off leakage current vs. temperature 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -40 -20 0 20 40 60 80 100 120 temperature (c) turn-off leakage current ( a) switch off supply current vs. temperature -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -40 -20 0 20 40 60 80 100 120 temperature (c) switch off supply current ( a) c in = c out = 33 f r l = 1k 4 v in = v en = 5v c in = c out = 33 f 4 v in = 5v, v en = 0v c in = c out = 33 f r l = 0 2 v en = 5v c in = c out = 33 f 4 v in = 5v, r l = 1 c i n = c out = 33 f s2 = on, s3 = off 5 v in = 5v, v en = 0v c in = c out = 33 f r l = open 2
rt9702/a 9 ds9702/a-15 april 2011 www.richtek.com v en (5v/div) v out (5v/div) i l (0.5a/div) time (100 s/div) turn- off response v in = 5v, r l = 30 c in = 33 f, c out = 1 f s1 = off 1 time (100 s/div) v en (5v/div) v out (1v/div) v in =5v, r l =30 c i n =33uf, c out =1uf s 1 = on turn- on response v in = 5v, r l = 30 c in = 33 f, c out = 1 f s1 = on 1 v in (1v/div) v out (1v/div) time (1ms/div) uvlo at rising v in = 5v, r l = 30 c in = 33 f, c out = 1 f v in v out 4 v in (1v/div) v out (1v/div) time (10 m s/div) uvlo at falling v in = 5v, r l = 30 c in = 33 f, c out = 1 f v in v out 4 i l (0.5a/div) v out (5v/div) time (100ms/div) ramped load response 4.9v 1.1a 5 v in = 5v r l = 1k 1 c in = 33 f, c out = 1 f v en (5v/div) i l (0.5a/div) time (50 s/div) soft- start response v in = 5v, r l =1 c in = 33 f, c out = 1 f 5 s2 : off on s3 = off
rt9702/a 10 ds9702/a-15 april 2011 www.richtek.com v in = 5v, r l = 1 c in = 33 f s2 = on, s3 = off short circuit current response time (10ms/div) 0 1 2 i out (a) 3 4 5 5 c out = 1000 f c out = 220 f c out = 1 f i out (1a/div) time (5 s/div) current limit transient respones v in = 5v, c in = c out = 33 f s2 = on, s3 = off, r l = 1 v trigger (5v/div) 5 time (50ms/div) s2 = on s3 = off r l = 1 c in = 33 f c out = 1 f s3 = on thermal shutdown response 5 i out (1a/div) short v en (5v/div) i out (1a/div) current limit time (10ms/div) 12ms (t d ) i l (1a/div) v out (5v/div) flag response v flg (5v/div) c in = 0.1 f, c out = 33 f r l = 1 , s1 = on 1 i l (0.5a/div) v en (5v/div) time (2.5ms/div) flag response (enable into short circuit) c in = 33 f, c out = 1 f r l = 0 , s1 = on v flg (5v/div) 12ms (t d ) rt9702cb 1
rt9702/a 11 ds9702/a-15 april 2011 www.richtek.com soft start for hot plug-in applications in order to eliminate the upstream voltage droop caused by the large inrush current during hot-plug events, the ? soft-start ? feature effectively isolates the power source from extremely large capacitive loads, satisfying the usb voltage droop requirements. fault flag the rt9702/a provides a flg signal pin which is an n- channel open drain mosfet output. this open drain output goes low when v out < v in ? 1v, current limit or the die temperature exceeds 130 c approximately. the flg output is capable of sinking a 10ma load to typically 200mv above ground. the flg pin requires a pull-up resistor, this resistor should be large in value to reduce energy drain. a 100k pull-up resistor works well for most applications. in the case of an over-current condition, flg will be asserted only after the flag response delay time, t d , has elapsed. this ensures that flg is asserted only upon valid over-current conditions and that erroneous error reporting is eliminated. for example, false over-current conditions may occur during hot-plug events when extremely large capacitive loads are connected and causes a high transient inrush current that exceeds the current limit threshold. the flg response delay time t d is typically 10ms. under-voltage lockout under-voltage lockout (uvlo) prevents the mosfet switch from turning on until input voltage exceeds approximately 1.7v. if input voltage drops below approximately 1.3v, uvlo turns off the mosfet switch, flg will be asserted accordingly. under-voltage detection functions only when the switch is enabled. current limiting and short-circuit protection the current limit circuitry prevents damage to the mosfet switch and the hub downstream port but can deliver load current up to the current limit threshold of typically 800ma through the switch of rt9702 and 1.5a for RT9702A respectively. when a heavy load or short circuit is applied to an enabled switch, a large transient current may flow applications information the rt9702 and RT9702A are single n-channel mosfet high-side power switches with active-high enable input, optimized for self-powered and bus-powered universal serial bus (usb) applications. the rt9702/a equipped with a charge pump circuitry to drive the internal nmos switch; the switch's low r ds(on) , 80m , meets usb voltage drop requirements; and a flag output is available to indicate fault conditions to the local usb controller. input and output v in (input) is the power source connection to the internal circuitry and the drain of the mosfet. v out (output) is the source of the mosfet. in a typical application, current flows through the switch from v in to v out toward the load. if v out is greater than v in , current will flow from v out to v in since the mosfet is bidirectional when on. unlike a normal mosfet, there is no a parasitic body diode between drain and source of the mosfet, the rt9702/a prevents reverse current flow if v out being externally forced to a higher voltage than v in when the output disabled (v en < 0.8v). chip enable input the switch will be disabled when the en pin is in a logic low condition. during this condition, the internal circuitry and mosfet are turned off, reducing the supply current to 0.1 a typical. the maximum guaranteed voltage for a logic low at the en pin is 0.8v. a minimum guaranteed voltage of 2v at the en pin will turn the rt9702/a back on. floating the input may cause unpredictable operation. en should not be allowed to go negative with respect to gnd. the en pin may be directly tied to v in to keep the part on. d g s d g s normal mosfet rt9702/a
rt9702/a 12 ds9702/a-15 april 2011 www.richtek.com thermal shutdown thermal shutdown is employed to protect the device from damage if the die temperature exceeds approxi- mately 130 c. if enabled, the switch automatically restarts when the die temperature falls 20 c. the output and flg signal will continue to cycle on and off until the device is disabled or the fault is removed. power dissipation the device s junction temperature depends on several factors such as the load, pcb layout, ambient temperature and package type. the output pin of rt9702/a can deliver a current of up to 500ma, and 1.1a respectively over the full operating junction temperature range. however, the maximum output current must be derated at higher ambient temperature to ensure the junction temperature does not exceed 125 c. with all possible conditions, the junction temperature must be within the range specified under operating conditions. power dissipation can be calculated based on the output current and the r ds(on) of switch as below. p d = r ds(on) x i out 2 although the devices are rated for 500ma and 1.1a of output current, but the application may limit the amount of output current based on the total power dissipation and the ambient temperature. the final operating junction temperature for any set of conditions can be estimated by the following thermal equation: p d (max) = (t j (max) ? t a ) / ja where t j (max) is the maximum junction temperature of the die (125 c) and t a is the maximum ambient temperature. the junction to ambient thermal resistance ( ja ) for sot-23-5 and tsot-23-5 pack age at recommended minimum footprint is 250 c/w ( ja is layout dependent). universal serial bus (usb) & power distribution the goal of usb is to be enabled device from different vendors to interoperate in an open architecture. usb features include ease of use for the end user, a wide range of workloads and applications, robustness, synergy with the pc industry, and low-cost implement- ation. benefits include self-identifying peripherals, dynamically attachable and reconfigurable peripherals, multiple connections (support for concurrent operation of many devices), support for as many as 127 physical devices, and compatibility with pc plug-and-play architecture. the universal serial bus connects usb devices with a usb host: each usb system has one usb host. usb devices are classified either as hubs, which provide additional attachment points to the usb, or as functions, which provide capabilities to the system (for example, a digital joystick). hub devices are then classified as either bus-power hubs or self-powered hubs. a bus-powered hub draws all of the power to any internal functions and downstream ports from the usb connector power pins. the hub may draw up to 500ma from the upstream device. external ports in a bus-powered hub can supply up to 100ma per port, with a maximum of four external ports. self-powered hub power for the internal functions and downstream ports does not come from the usb, although the usb interface may draw up to 100ma from its upstream connect, to allow the interface to function when the remainder of the hub is powered down. the hub must be able to supply up to 500ma on all of its external downstream ports. please refer to universal serial specification revision 2.0 for more details on designing compliant usb hub and host systems. over current protection devices such as fuses and ptc resistors (also called polyfuse or polyswitch) have slow trip times, high on-resistance, and lack the necessary circuitry for usb-required fault reporting. the faster trip time of the rt9702/a power distribution allow designers to design hubs that can operate through faults. the rt9702/a have low on-resistance and internal fault-reporting circuitry that help the designer to meet voltage regulation and fault notification requirements. until the current limit circuitry responds. once this current limit threshold is exceeded the device enters constant current mode until the thermal shutdown occurs or the fault is removed.
rt9702/a 13 ds9702/a-15 april 2011 www.richtek.com output filter capacitor a low-esr 150 f aluminum electrolytic or tantalum between v out and gnd is strongly recommended to meet the 330mv maximum droop requirement in the hub v bus (per usb 2.0, output ports must have a minimum 120 f of low-esr bulk capacitance per hub). standard bypass methods should be used to minimize inductance and resistance between the bypass capacitor and the downstream connector to reduce emi and decouple voltage droop caused when downstream cables are hot-insertion transients. ferrite beads in series with v bus , the ground line and the 0.1 f bypass capacitors at the power connector pins are recommended for emi and esd protection. the bypass capacitor itself should have a low dissipation factor to allow decoupling at higher frequencies. fault flag filtering (optional) the transient inrush current to downstream capacitance may cause a short-duration error flag, which may cause erroneous over-current reporting. a simple 1ms rc low- pass filter (10k and 0.1 f) in the flag line (see typical application circuit) eliminates short-duration transients. voltage drop the usb specification states a minimum port-output voltage in two locations on the bus, 4.75v out of a self- powered hub port and 4.40v out of a bus-powered hub port. as with the self-powered hub, all resistive voltage drops for the bus-powered hub must be accounted for to guarantee voltage regulation (see figure 7-47 of universal serial specification revision 2.0 ). the following calculation determines v out (min) for multi- ple ports ( n ports ) ganged together through one switch (if using one switch per port, n ports is equal to 1) : v out (min) = 4.75v ? [ i i x ( 4 ? r conn + 2 ? r cable ) ] ? (0.1a x n ports x r switch ) ? v pcb where r conn = resistance of connector contacts (two contacts per connector) r cable = resistance of upstream cable wires (one 5v and one gnd) r switch = resistance of power switch (80m typical for rt9702/a) v pcb = pcb voltage drop the usb specification defines the maximum resistance per contact ( r conn ) of the usb connector to be 30m and the drop across the pcb and switch to be 100mv. this basically leaves two variables in the equation: the resistance of the switch and the resistance of the cable. if the hub consumes the maximum current ( i i ) of 500ma, the maximum resistance of the cable is 90m . the resistance of the switch is defined as follows: r switch = { 4.75v - 4.4v -[ 0.5a x ( 4 ? 30m + 2 ? 90m ) ]-v pcb } ( 0.1a x n ports ) = (200mv - v pcb ) ( 0.1a x n ports ) if the voltage drop across the pcb is limited to 100mv, the maximum resistance for the switch is 250m for four ports ganged together. the rt9702/a, with its maximum 100m on-resistance over temperature, easily meets this requirement. because the devices are also power switches, the designer of self-powered hubs has the flexibility to turn off power to output ports. unlike a normal mosfet, the devices have controlled rise and fall times to provide the needed inrush current limiting required for the bus-powered hub power switch. supply filter/bypass capacitor a 1 f low-esr ceramic capacitor from v in to gnd, located at the device is strongly recommended to prevent the input voltage drooping during hot-plug events. however, higher capacitor values will further reduce the voltage droop on the input. furthermore, without the bypass capacitor, an output short may cause sufficient ringing on the input (from source lead inductance) to destroy the internal control circuitry. the input transient must not exceed 6.5v of the absolute maximum supply voltage even for a short duration.
rt9702/a 14 ds9702/a-15 april 2011 www.richtek.com esd because usb is a hot insertion and removal system, usb components (especially the connector pins) are subject to electrostatic discharge (esd) and should be qualified to iec801.2. the rt9702/a is designed to withstand a 8kv human body mode, as defined in mil-std-883c. the requirements in iec801.2 are much more stringent and require additional capacitors for the rt9702/a to withstand the higher esd energy. low-esr 1 f ceramic bypass capacitors and output capacitors should be placed as closely as possible to the v in and v out pins to increase the esd immunity. the rt9702/a may pass the requirements of iec 1000-4-2 (en 50082-1) level-4 for 15kv air discharge and 8kv contact discharge tests when these capacitors are added. pcb layout in order to meet the voltage drop, droop, and emi requirements, careful pcb layout is necessary. the following guidelines must be considered: z keep all v bus traces as short as possible and use at least 50-mil, 2 ounce copper for all v bus traces. z avoid vias as much as possible. if vias are necessary, make them as large as feasible. z place a ground plane under all circuitry to lower both resistance and inductance and improve dc and transient performance (use a separate ground and power plans if possible). z place cuts in the ground plane between ports to help reduce the coupling of transients between ports. z locate the output capacitor and ferrite beads as close to the usb connectors as possible to lower impedance (mainly inductance) between the port and the capacitor and improve transient load performance. z locate the rt9702/a as close as possible to the output port to limit switching noise. z locate the ceramic bypass capacitors as close as possible to the v in pins of the rt9702/a. gnd en flg gnd_bus usb controller board layout v in v out v bus
rt9702/a 15 ds9702/a-15 april 2011 www.richtek.com outline dimension a a1 e b b d c h l sot-23-5 surface mount package dimensions in millimeters dimensions in inches symbol min max min max a 0.889 1.295 0.035 0.051 a1 0.000 0.152 0.000 0.006 b 1.397 1.803 0.055 0.071 b 0.356 0.559 0.014 0.022 c 2.591 2.997 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024
rt9702/a 16 ds9702/a-15 april 2011 www.richtek.com richtek technology corporation headquarter 5f, no. 20, taiyuen street, chupei city hsinchu, taiwan, r.o.c. tel: (8863)5526789 fax: (8863)5526611 richtek technology corporation taipei office (marketing) 5f, no. 95, minchiuan road, hsintien city taipei county, taiwan, r.o.c. tel: (8862)86672399 fax: (8862)86672377 email: marketing@richtek.com information that is provided by richtek technology corporation is believed to be accurate and reliable. richtek reserves the ri ght to make any change in circuit design, specification or other related things if necessary without notice at any time. no third party intellectual property inf ringement of the applications should be guaranteed by users when integrating richtek products into any application. no legal responsibility for any said applications i s assumed by richtek. tsot-23-5 surface mount package dimensions in millimeters dimensions in inches symbol min max min max a 0.700 1.000 0.028 0.039 a1 0.000 0.100 0.000 0.004 b 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 c 2.591 3.000 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024 a a1 e b b d c h l

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