MAX1823A MAX1823B MAX1823H INPUT 4V TO 5.5V. Maxim Integrated Products 1

Transcription

1 19-193; Rev 3; 1/3 Dual US Switch with Fault General Description The MX1823 is a dual, current-limited switch with autoreset specifically made for US applications. The autoreset feature latches the switch off if the output is shorted, saving system power. The switch reactivates when the short circuit is removed. Each channel is guaranteed to supply 72m and meet US specifications. Low quiescent supply current (5µ) and standby current (3µ) conserve battery power in portable applications. The MX1823 has multiple safety features to ensure that the US port is protected. uilt-in thermal-overload protection limits power dissipation and junction temperature. ccurate internal current-limiting circuitry protects the input supply against both overload and short-circuit conditions. Independent fault signals (FULT and FULT) notify the microprocessor (µp) when a thermal-overload, current-limit, undervoltagelockout (UVLO), or short-circuit fault occurs. 2ms fault-blanking feature ignores momentary faults, such as those caused when hot swapping a capacitive load, preventing false alarms to the host system. The MX1823/MX1823 also block reverse current (current from OUT_ to IN_) while in shutdown. The MX1823 is available in a space-saving 1-pin µmx package. The MX1823/MX1823 are enabled with an active-low signal, and the MX1823/MX1823H are enabled with an active-high signal. For a single version of this device, refer to the MX1946 data sheet. For a triple version, refer to the MX194 data sheet. US Ports and Hubs Notebook and Desktop omputers PDs and Palmtop omputers Docking Stations TOP VIEW *(ON) ON IN IN IN *(ON) ON *( ) RE FOR MX1823/MX1823H. pplications Pin onfiguration MX1823 MX1823 MX1823 MX1823H µmx 1 FULT 9 OUT 8 GND 7 OUT 6 FULT Features Dual US Switch in Tiny 1-Pin µmx Package utoreset Feature Saves Power Guaranteed 72m Load per hannel uilt-in 2ms Fault lanking ompliant to US Specification locks Reverse urrent in Shutdown (MX1823/MX1823) 4V to 5. Input Voltage Range Independent Shutdown ontrol (MX1823/MX1823 ctive Low) (MX1823/MX1823H ctive High) Independent FULT Indicator Outputs Thermal-Overload Protection 5µ Quiescent urrent (oth Switches On) 3µ Standby urrent UL Recognized Ordering Information PRT TEMP RNGE PIN-PKGE MX1823EU -4 to µmx MX1823EU -4 to µmx MX1823EU -4 to µmx MX1823HEU -4 to µmx INPUT 4V TO 5. Typical Operating ircuit ON ON IN IN IN FULT FULT ON ON MX1823 MX1823 GND OUT OUT US PORT US PORT Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at , or visit Maxim s website at

2 SOLUTE MXIMUM RTINGS IN, IN, IN, ON, ON, ON, ON OUT, OUT to GND...-.3V to +6V FULT, FULT to GND...-.3V to (V IN_ +.3V) MX1823/MX1823H, IN, IN to OUT; IN, IN to OUT...-.3V to +6V MX1823/MX1823, IN, IN to OUT; IN, IN to OUT (when disabled, Note 3)...-6V to +6V IN, IN to OUT; IN, IN to OUT (when enabled, Note 4) to +1.5 RMS Stresses beyond those listed under bsolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and 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 affect device reliability. ELETRIL HRTERISTIS FULT, FULT urrent...2m ontinuous Power Dissipation (T = +7 ) 1-Pin µmx (derate 5.6mW/ above +7 )...444mW Operating Temperature Range...-4 to +85 Junction Temperature Storage Temperature Range to +15 Lead Temperature (soldering, 1s)...+3 (ircuit of Figure 1, V IN = V IN = V IN =, ON = ON = GND (MX1823/MX1823), ON = ON = IN (MX1823/MX1823H), T = to +85, unless otherwise noted. Typical values are at T = +25.) PRMETER SYMOL ONDITIONS MIN TYP MX UNITS Supply Voltage Range V Switch On-Resistance Standby Supply urrent Quiescent Supply urrent OUT_ Off-Leakage urrent R ON T = +25, each switch, MX1823/MX1823H T = +25, each switch, MX1823/MX1823 T = to +85, each switch, MX1823/MX1823H T = to +85, each switch, MX1823/MX1823 ON_ = IN_ (MX1823/MX1823), ON_ = GND (MX1823/MX1823H) mω 3 1 µ I OUT = I OUT =, one channel on 4 8 I OUT = I OUT =, both channels on 5 1 ON_ = IN _ ( MX 1823/M X1823), ON _ = GND (M X1823/M X1823H), V OUT = V OUT = V, T = +25 o ON_ = IN_ (MX1823/MX1823), ON_ = GND (MX1823/MX1823H), V OUT = V OUT = V, T = o to +85 o Undervoltage-Lockout Threshold V UVLO Rising edge, 3% hysteresis V ontinuous Load urrent 72 m ontinuous urrent Limit I LIM V IN - V OUT_ = V OUT_ = V (I OUT pulsing) PEK Short-ircuit urrent Limit I SHORT V OUT_ = V (I OUT pulsing).35 RMS µ µ 2

3 ELETRIL HRTERISTIS (continued) (ircuit of Figure 1, V IN = V IN = V IN =, ON = ON = GND (MX1823/MX1823), ON = ON = IN (MX1823/MX1823H), T = to +85, unless otherwise noted. Typical values are at T = +25.) PRMETER SYMOL ONDITIONS MIN TYP MX UNITS Short-ircuit Detect Threshold (Note 1) 1 V ontinuous urrent-limit lanking Timeout Period Short-ircuit lanking Timeout Period From continuous current-limit condition to FULT_ assertion From short-circuit current-limit condition to FULT_ assertion ms ms Turn-On Delay t ON does not include R OUT_ = 1kΩ, MX1823/MX1823H rise time MX1823/MX Output Rise Time t RISE R OUT_ = 1Ω, from 1% to 9% of V OUT_ 2.5 ms R OUT _ = 1Ω, does not include fall time (from ON_ (MX1823) or ON_ (MX1823H) deasserted to V OUT = 9% of V IN_ ) OFF R OUT _ = 1Ω, does not include fall time (from ON_ (MX1823) or ON_ (MX1823) deasserted to V OUT = 9% of V IN_ ) R OUT_ = 1Ω, from 9% to 1% of V OUT_ (MX1823/MX1823H) Output Fall Time t FLL R OUT_ = 1Ω, from 9% to 1% of V OUT_ (MX1823/MX1823) Thermal-Shutdown Threshold 15 o hysteresis Logic Input High Voltage V IN_ = 4V to 5. 2 V Logic Input Low Voltage V IN_ = 4V to 5..8 V Logic Input urrent ON_ = GND or IN_ (MX1823/MX1823), ON_ = GND or IN_ (MX1823/MX1823H) ms ms ms o µ FULT_ Output Low Voltage I SINK = 1m, V IN _ = 4V.4 V FULT_ Output High Leakage urrent V IN _ = V FULT_ = 5. 1 µ utoreset OUT_ urrent In latched-off state, V OUT_ = V m utoreset Threshold In latched-off state, rising V utoreset lanking Time In latched-off state, V OUT_ > ms 3

4 ELETRIL HRTERISTIS (ircuit of Figure 1, V IN = V IN _ = V ON _ = (MX1823/MX1823H); V IN = V IN _ =, ON_ = GND (MX1823/MX1823), T = -4 to +85, unless otherwise noted.) (Note 2) PRMETER SYMOL ONDITIONS MIN TYP MX UNITS Supply Voltage Range V Each switch, MX1823/MX1823H 135 Switch On-Resistance R ON Each switch, MX1823/MX Standby Supply urrent Quiescent Supply urrent OUT_ Off-Leakage urrent ON_ = IN_ (MX1823/MX1823), ON_ = GND (MX1823/MX1823H) I OUT = I OUT =, one channel on 8 I OUT = I OUT =, both channels on 1 ON_ = IN_ (MX1823/MX1823), ON_ = GND (MX1823/MX1823H), V OUT = V OUT = V mω 1 µ µ 1 µ Undervoltage-Lockout Threshold V UVLO Rising edge, 3% hysteresis V ontinuous Load urrent 72 m ontinuous urrent Limit I LIM V IN_ - V OUT_ = urrent Limit into Short ircuit I SHORT V OUT_ = V (I OUT pulsing) PEK ontinuous urrent-limit lanking Timeout Period Short-ircuit lanking Timeout Period From continuous current-limit condition to FULT_ assertion From short-circuit current-limit condition to FULT_ assertion 1 35 ms ms Turn-On Delay t ON does not include R OUT_ = 1kΩ, MX1823/MX1823H.5 4. rise time MX1823/MX Turn-Off Delay from ON t OFF (from ON_ (MX1823/MX1823) or ON_ (MX1823/MX1823H) deasserted to R OUT_ = 1Ω, does not include fall time V OUT_ = 9% V IN_ ) ms 3 ms 4

5 ELETRIL HRTERISTIS (continued) (ircuit of Figure 1, V IN = V IN _ = V ON _ = (MX1823/MX1823H); V IN = V IN _ =, ON_ = GND (MX1823/MX1823), T = -4 to +85, unless otherwise noted.) (Note 2) PRMETER SYMOL ONDITIONS MIN TYP MX UNITS Logic Input High Voltage V IN_ = 4V to 5. 2 V Logic Input Low Voltage V IN_ = 4V to 5..8 V Logic Input urrent V ON_ = V or V IN_ µ FULT_ Output Low Voltage I SINK = 1m, V IN_ = 4V.4 V FULT_ Output High Leakage urrent V IN_ = V FULT_ = 5. 1 µ utoreset OUT_urrent In latched-off state, V OUT_ = V 1 5 m utoreset Threshold In latched-off state, rising.4.6 V utoreset lanking Time In latched-off state, V OUT_ > ms Note 1: The output voltage at which the device transitions from short-circuit current limit to continuous current limit. Note 2: Specifications to -4 are guaranteed by design, not production tested. Note 3: Reverse current (current from OUT_ to IN_) is blocked when disabled. Note 4: Forward current (current from IN_ to OUT_) is internally limited. Reverse current, from OUT_ to IN_, is not limited when the device is enabled and must be kept below 1.5 RMS to prevent permanent device damage. When the MX1823/MX1823 are disabled, the switch turns off and reverse current is internally blocked. Typical Operating haracteristics (ircuit of Figure 1, V IN = V IN = V IN =, ON_ = GND (MX1823/MX1823), ON_ = IN_ (MX1823/MX1823H), T = +25, unless otherwise noted.) QUIESENT URRENT (µ) QUIESENT URRENT vs. INPUT VOLTGE INPUT VOLTGE (V) MX1823 toc1 QUIESENT URRENT (µ) QUIESENT URRENT vs. TEMPERTURE V IN _ = 5. V IN _ = V IN _ = MX1823 toc2 SHUTDOWN SUPPLY URRENT (µ) SHUTDOWN SUPPLY URRENT vs. TEMPERTURE ON_ = IN_ (MX1823/MX1823) ON_ = GND (MX1823/MX1823H) MX1823 toc3 5

6 Typical Operating haracteristics (continued) (ircuit of Figure 1, V IN = V IN = V IN =, ON_ = GND (MX1823/MX1823), ON_ = IN_ (MX1823/MX1823H), T = +25, unless otherwise noted.) SWITH OFF-LEKGE (n) FULT_ OUTPUT LOW VOLTGE (V) TURN-ON TIME (ms) SWITH OFF-LEKGE vs. TEMPERTURE TURN-ON TIME vs. TEMPERTURE (t ON + t RISE ) V IN _ = 4. V IN _ = 5. V IN _ = FULT_ OUTPUT LOW VOLTGE vs. TEMPERTURE I FULT _ = 1m V IN _ = 4. V IN _ = V IN _ = MX1823 toc4 MX1823 toc7 MX1823 toc1 NORMLIZED RON TURN-OFF TIME (ms) UTORESET URRENT (m) NORMLIZED R ON vs. TEMPERTURE TURN-OFF TIME vs. TEMPERTURE (t OFF + t FLL ) V IN _ = V IN _ = 4. V IN _ = UTORESET URRENT vs. TEMPERTURE (MX1823/MX1823H) V IN _ = 4. V IN _ = 5. V IN _ = MX 1823 toc5 MX1823 toc8 MX1823 toc11 ONTINUOUS URRENT LIMIT (m) FULT-LNKING TIME (ms) UTORESET URRENT (m) ONTINUOUS URRENT-LIMIT THRESHOLD vs. TEMPERTURE V IN_ = 5. V IN_ = V IN_ = FULT-LNKING TIME vs. TEMPERTURE V IN _ = 4. V IN _ = 5. V IN _ = UTORESET URRENT vs. TEMPERTURE (MX1823/MX1823) V IN _ = 4. V IN _ = 5. V IN _ = MX1823 toc6 MX1823 toc9 MX1823 toc12 6

7 Typical Operating haracteristics (continued) (ircuit of Figure 1, V IN = V IN = V IN =, ON_ = GND (MX1823/MX1823), ON_ = IN_ (MX1823/MX1823H), T = +25, unless otherwise noted.) UTORESET URRENT (m) D UTORESET URRENT vs. INPUT VOLTGE (MX1823/MX1823H) T = INPUT VOLTGE (V) T = -4 T = +85 OVERLOD RESPONSE INTO 2.5Ω (MX1823/MX1823 ONLY) : V IN_, /div : V OUT, /div 1ms/div : V FULT, /div D: I OUT, 1/div MX1823 toc16 SHORT-IRUIT RESPONSE INTO Ω (MX1823/MX1823) MX1823 toc19 MX1823 toc13 UTORESET URRENT (m) D UTORESET URRENT vs. INPUT VOLTGE (MX1823/MX1823) T = +25 T = -4 T = INPUT VOLTGE (V) OVERLOD RESPONSE INTO 2.5Ω (EXPNDED TIME SLE) : V IN_, /div : V OUT, /div 5µs/div : V FULT, /div D: I OUT, 1/div MX1823 toc17 SHORT-IRUIT RESPONSE INTO Ω (EXPNDED TIME SLE) MX1823 toc2 MX1823 toc14 D D OVERLOD RESPONSE INTO 2.5Ω (MX1823/MX1823H) MX1823 toc15 1ms/div : V IN_, /div : V FULT, /div : V OUT, /div D: I OUT, 1/div SHORT-IRUIT RESPONSE INTO Ω (MX1823/MX1823H) 1ms/div : V IN _, /div : V FULT, /div : V OUT, /div D: I OUT, 1/div SWITH TURN-ON TIME (MX1823/MX1823) MX1823 toc18 MX1823 toc21 D D : V IN _, /div : V OUT, /div 1ms/div : V FULT, /div D: I OUT, 2/div : V IN_, /div : V OUT, /div 5µs/div : V FULT, /div D: I OUT, 2/div : V ON, /div : V OUT, 2V/div 1ms/div 7

8 Typical Operating haracteristics (continued) (ircuit of Figure 1, V IN = V IN = V IN =, ON_ = GND (MX1823/MX1823), ON_ = IN_ (MX1823/MX1823H), T = +25, unless otherwise noted.) PIN NME FUNTION 1 2, 3, 4 5 : V ON, /div : V OUT, 2V/div ON *(ON) IN, IN, IN ON *(ON) 6 FULT 7 OUT 8 GND Ground 9 OUT 1 FULT SWITH TURN-OFF TIME (t OFF + t FLL ) 1ms/div *() are for the MX1823/MX1823H only. MX1823 toc22 STRTUP TIME (TYPIL US PPLITION) : V ON, /div : V FULT, /div 5µs/div Pin Description ontr ol Inp ut for S w i tch. an b e d r i ven hi g her than IN_ w i thout d am ag e. l og i c l ow tur ns sw i tch on for the M X 1823/M X 1823, and a l og i c hi g h tur ns sw i tch on for the M X 1823/M X 1823H. Power Input. onnect all IN_ pins together, and bypass with a.1µf capacitor to ground. Load conditions may require additional bulk capacitance to prevent the input from being pulled down. ontrol Input for Switch. an be driven higher than IN_ without damage. logic low turns switch on for the M X 1823/M X 1823, and a logic high turns switch on for the M X 1823/M X 1823H. Fault-Indicator Output for Switch. This open-drain output goes low when switch is in thermal shutdown or UVLO or in a sustained (>2ms) current-limit or short-circuit condition. Power Output for Switch. onnect a 1µF capacitor from OUT to ground. Load condition may require additional bulk capacitance. Power Output for Switch. onnect a 1µF capacitor from OUT to ground. Load condition may require additional bulk capacitance. Fault-Indicator Output for Switch. This open-drain output goes low when switch is in thermal shutdown or UVLO or in a sustained (>2ms) current-limit or short-circuit condition. D : V OUT, 2V/div D : I OUT,.5/div MX1823 toc23 8

9 Detailed Description The MX1823 is a dual, current-limited switch designed for US applications. It has two independent switches, each with its own enable control input and autoreset function. Each switch has an error-flag output to notify the US controller when the current-limit, short-circuit, undervoltage-lockout, or thermal-shutdown threshold is reached (Figure 2). The MX1823 operates from a 4V to 5. input voltage range and guarantees a minimum 72m output current. built-in.9 current limit limits the current in the event of a heavy-overload condition. The MX1823 has independent thermal shutdown for each switch in the event of a prolonged overload or short-circuit condition. The autoreset function monitors the overload and automatically turns the switch on when the overload is removed. Use of low-r ON NMOS switches enables the MX1823 to provide two switches in the ultra-small 1-pin µmx package. n internal micropower charge pump generates the high-side supply needed for driving the gates of these high-side switches. Separate current-limiting and thermal-shutdown circuits permit each switch to operate independently, improving system robustness. Undervoltage-Lockout and Input-Voltage Requirements The MX1823 includes a UVLO circuit to prevent erroneous switch operation when the input voltage goes low during startup and brownout conditions. Operation is inhibited when V IN_ is less than 3.4V. Output Fault Protection The MX1823 senses the switch output voltage and selects continuous current limiting when V OUT is greater than 1V or short-circuit current limiting when V OUT is less than 1V. When V OUT is greater than 1V, the device operates in a continuous current-limit mode that sets the output current limit to.9. When V OUT is less than 1V, the device operates in short-circuit current-limit mode, sourcing.35 RMS current pulses to the load. utoreset Mode If an output fault is detected for more than the 2ms blanking time, the output latches off, the FULT_ output goes low, and a 25m current is forced at the output. If the voltage on the output exceeds. for 2ms, the fault resets, the 25m current source shuts down, and the output turns on. The device monitors the output voltage so that a short-circuit condition can be detected. ctive loads are not expected to have measurable currents when the supply is below.. The MX1823/MX1823 can also be reset from fault manually by toggling ON_ (ON_ for the MX1823/MX1823H) for that channel. Thermal Shutdown The MX1823 features independent thermal shutdown for each switch channel, allowing one switch to deliver power even if the other switch has a fault condition. When the junction temperature exceeds +16, the switch turns off and the FULT_ output goes low immediately; fault blanking does not occur during thermal limit. When the junction cools by 15, the switch turns on again. If the fault overload condition continues, the switch cycles on and off, resulting in a pulsed output, saving battery power. Reverse urrent locking The US specification does not allow an output device to source current back into the US port. However, the MX1823/MX1823 are designed to safely power noncompliant devices. When disabled, each output is switched to a high-impedance state, blocking reverse current flow from the output back to the input. However, during normal operation with the device enabled, the MX1823/MX1823 are bidirectional switches. Fault Indicators The MX1823 provides an open-drain fault output (FULT_) for each switch. For most applications, connect FULT_ to IN_ through a 1kΩ pullup resistor. FULT_ goes low when any of the following conditions occur: The input voltage is below the UVLO threshold. The switch junction temperature exceeds the +16 thermal-shutdown temperature limit. The switch is in current-limit or short-circuit limit mode after the fault-blanking period is exceeded. The switch is in autoreset mode. INPUT 4V TO 5..1µF 1kΩ 1kΩ ON ON * US PPLITIONS MY REQUIRE DDITIONL ULK PITNE. IN IN IN FULT FULT ON ON Figure 1. Typical pplication ircuit MX1823 GND OUT OUT US PORT 1µF* US PORT 1µF* 9

10 fter the fault condition is removed, the FULT_ output deasserts after a 2ms delay. Ensure that the MX1823 has adequate input bypass capacitance to prevent glitches from triggering FULT_ outputs. Input glitches greater than.2v/µs may cause erroneous FULT_ indications. ehavior During urrent Limit and Fault lanking The MX1823 limits switch current in three ways. When ON_ is deasserted (high for MX1823/MX1823, low for MX1823/MX1823H), the switch is off and leakage dominates the residual output current. When ON_ is asserted (low for MX1823/MX1823, high for MX1823/MX1823H), the switch supplies a continuous output current of at least 72m. When the output current exceeds the.9 threshold, the MX1823 limits the current depending on the output voltage. For V OUT_ greater than 1V (current-limit mode), the MX1823 regulates the output current to.9. For 4V TO 5. IN_.1µF IN ON *(ON) *(ON) ON IN HRGE PUMP IS UVLO REF OS 25kHz MX1823/MX1823 MX1823/MX1823H HRGE PUMP V OUT_ less than 1V (short-circuit mode), the MX1823 pulses the switch, decreasing the current to.35 RMS (Table 1). Note that a thermal overload may result from either of these high-current conditions. The MX1823 switches may enter current limit in normal operation when powering up or driving heavy capacitive loads. To differentiate these conditions from short circuits or sustained overloads that may damage the device, the MX1823 has an independent faultblanking circuit in each switch. When a load transient causes the device to enter current limit, an internal counter starts to monitor the duration of the fault. For load faults exceeding 2ms fault-blanking time, the switch turns off, the FULT_ signal asserts low, and the device enters autoreset mode (see the utoreset Mode section). Only current-limit and short-circuit faults are blanked. Thermal-overload faults and input voltage drops below the UVLO threshold immediately cause the switch to turn off and FULT_ to assert low. THERML SHUTDOWN TIMER 2ms ILIM 25m FULT LOGI 25m ILIM FULT IN 1µF GND 1µF IN OUT OUT *( ) RE FOR THE MX1823/MX1823H. FULT Figure 2. Functional Diagram 1

11 Table 1. MX1823 urrent Limiting and Fault ehavior ONDITION Output short circuit (V OUT < 1V) Output overload current (V OUT > 1V) Thermal fault (T J > +16 ) Fault blanking allows the MX1823 to handle US loads that may not be fully compliant with the US specifications. US loads with additional bypass capacitance and/or large startup currents can be successfully powered even while protecting the upstream power source. No fault is indicated if the switch is able to bring up the load within the 2ms blanking period. pplications Information Input Power Source IN, IN, and IN provide the power for all control and charge-pump circuitry. ll three IN_ pins must be connected together externally. The input-voltage slew rate should be less than.2v/µs to prevent erroneous FULT_ indications. This condition should not occur under normal US applications. Input apacitor onnect a capacitor from IN_ to ground to limit the input voltage drop during momentary output short-circuit conditions..1µf ceramic capacitor is required for local decoupling; higher capacitor values further reduce the voltage drop at the input (see the Typical pplication ircuit (Figure 1)). When driving inductive loads, a larger capacitance prevents voltage spikes from exceeding the MX1823 s absolute maximum ratings. MX1823 EHVIOR n output short circuit ramps the current to I SHORT in 2ms to 3ms, the switch shuts off, the blanking timer turns on, FULT_ stays high, and the output current pulses at.35 RMS. Removing the short circuit before the 15ms short-circuit blanking timeout period allows the next ramped current pulse to soft-start the output. The FULT_ flag stays high. short circuit exceeding 15ms to 2ms forces FULT_ low at 2ms, enables autoreset mode, and sources 25m at the output. n output voltage above. for 2ms resets the switch, turns on the output, and forces FULT_ high. n output overload regulates the current at I LIM (.9), and FULT_ stays high until the overload is removed, a thermal fault occurs, or the 2ms continuous current-limit timeout period is reached. n overcurrent condition still present at 2ms forces FULT_ low, enables autoreset, and sources 25m at the output. n output voltage above. for 2ms resets the switch, turns on the output, and forces FULT_ high. junction temperature of +16 immediately forces FULT_ low (the blanking timer does not apply to thermal faults) and turns off the switch. The junction cooling 15 removes the thermal fault condition, enables autoreset mode, and sources 25m at the output. FULT_ remains low while a thermal fault condition is present. n output voltage above. for 2ms resets the switch, turns on the output, and forces FULT_ high. Output apacitor Place a 1µF or greater capacitor at each output for noise immunity. When starting up into very large capacitive loads, the switch pulses the output current at.35 RMS until the output voltage rises above 1V, then the capacitor continues to charge at the full.9 current limit. There is no limit to the output capacitor size, but to prevent a startup fault assertion, the capacitor must charge up within the fault-blanking delay period. Typically, starting up into a 33µF or smaller capacitor does not trigger a fault output. In addition to bulk capacitance, small-value (.1µF or greater) ceramic capacitors improve the output s resilience to electrostatic discharge (ESD). Driving Inductive Loads wide variety of devices (mice, keyboards, cameras, and printers) can load the US port. These devices commonly connect to the port with cables, which can add an inductive component to the load. This inductance causes the output voltage at the US port to ring during a load step. The MX1823 is capable of driving inductive loads, but avoids exceeding the device s absolute maximum ratings. Usually the load inductance is relatively small, and the MX1823 s input includes a substantial bulk capacitance from an upstream regulator as well as local bypass capacitors, limiting overshoot. If severe ringing occurs due to large load inductance, clamp the MX1823 s output below 6V and above -.3V. 11

12 Turn-On and Turn-Off ehavior In the absence of faults, the MX1823 s internal switches turn on and off slowly under the control of the ON_ inputs. Transition times for both edges are provided in the Electrical haracteristics table. The slow chargepump switch drive minimizes load transients on the upstream power source. Under thermal fault and UVLO, the power device turns off rapidly (1ns) to protect the power device. Layout and Thermal Dissipation To optimize the switch response time to output shortcircuit conditions, keep all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors no more than 5mm from device leads. ll IN_ and OUT_ pins must be connected with short traces to the power bus. Wide power-bus planes provide superior heat dissipation through the switch IN_ and OUT_ pins. While the switches are on, power dissipation is small, and the package temperature change is minimal. alculate the power dissipation for this condition as follows: P = (I OUT_ ) 2 R ON For the normal operating current (I OUT_ =.5), and the maximum on-resistance of the switch (135mΩ), the power dissipation is: P = (.5) 2 x.135ω = 34mW per switch The worst-case power dissipation occurs when the switch is in current limit and the output is greater than 1V. In this case, the power dissipated in each switch is the voltage drop across the switch multiplied by the current limit: P = (I LIM ) (V IN - V OUT ) For a input and 1V output, the maximum power dissipation per switch is: P = (1.2) ( - 1V) = 4.8W Since the package power dissipation is only 444mW, the MX1823 die temperature exceeds the thermalshutdown threshold, and the switch output shuts down until the junction temperature cools by 15. The duty cycle and period are strong functions of the ambient temperature and the P board layout. short circuit at the output causes the power dissipated across the switch and the junction temperature to increase. If the fault condition persists, the thermaloverload-protection circuitry activates, and the output shuts down until the junction temperature decreases by 15 (see the Thermal Shutdown section). Since the output short-circuit current is 25m (typ), and with V IN_ =, calculate the power dissipation for a short-circuited output as follows: P = (.25)(5) =.125W hip Information TRNSISTOR OUNT: 3227 PROESS: imos 12

13 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to e ÿ.5±.1.6±.1 TOP VIEW D2 D1 b FRONT VIEW 1 4X S H GGE PLNE α OTTOM VIEW E2 E1 1 1 SIDE VIEW L L1 DIM 1 MIN -.2 MX.43.6 MIN -.5 MX D D2 E1 E2 H L L1 b e c S α c PROPRIETRY INFORMTION TITLE: PKGE OUTLINE, 1L umx/usop PPROVL INHES REF.94 REF S.5 S REF.498 REF 6 6 DOUMENT ONTROL NO. MILLIMETERS REV I 1 1 1LUMX.EPS Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, Maxim Integrated Products Printed US is a registered trademark of Maxim Integrated Products.

14 Mouser Electronics uthorized Distributor lick to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MX1823EU+ MX1823EU+T MX1823EU+ MX1823EU+T MX1823EU MX1823EU-T