PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator General Description Features The AAT4702 SmartSwitchTM is a member of AnalogicTech's Application Specific Power MOSFETTM (ASPMTM) product family. This device integrates a high side P-channel MOSFET current limiting load switch with a nanopower low dropout (LDO) linear voltage regulator, making the AAT4702 ideal for use in load current protected applications that also require a system power supply. The load switch operates with input voltages ranging from 2.4V to 5.5V, making it ideal for 2.5V, 3V, and 5V systems. A fault flag is provided to alert the system to an overcurrent event. The fault flag has a 5ms blanking time to prevent from reporting false events such as inrush currents during system startup. Load Switch: * 2.4V-5.5V Input Voltage Range * 150mA Default Current Limit Level * 270m Typical RDS(ON) at 2.4V * 400ns Response to Short Circuit * Reverse Voltage Protection * Current Limit Shutdown with Output Pull Down * Auto Restart with 40ms Timer * 5ms Fault Blanking Timeout * Under-Voltage Lockout Protection LDO Regulator: * Output Current up to 100mA * 1.8V Output Voltage with 2% Accuracy * Thermal and Short Circuit Protection * Active Shutdown Output Pull-Down * Low Quiescent Current 15A Typical for Switch and LDO * Less than 1A Shutdown Current * Only 1F Ceramic Output Capacitor Required * Available in FTDFN22-8L Package. The load switch current limit is 150mA by default or programmed up to 1A through an external set resistor. The AAT4702 LDO linear regulator is designed to deliver a regulated 1.8V supply voltage for load levels up to 100mA. The regulator section may be powered directly from an input source supply or from the load switch output. The AAT4702 is offered in a Pb-free, space-saving 8-pin 2x2mm FTDFN22 package, and is specified for operation over the -40C to +85C ambient temperature range. Applications * * * * * * Cell Phones Device Peripheral Ports Fingerprint Sensors Hot Swap Supplies Media Players Notebook Computers Typical Application INPUT IN N/C FAULT FLAG 4702.2009.02.1.2 OUTPUT AAT4702 1F ENABLE OUT IN_REG SET ON / ON FLT LDO REG OUTPUT VREG GND 1F www.analogictech.com 1F 1 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Pin Descriptions Pin # Symbol 1 OUT 2 IN_REG 3 4 VREG GND 5 SET 6 FLT 7 ON (ON) 8 IN Description Current limited P-channel MOSFET load switch output. A 0.47F to 1F ceramic capacitor connected from OUT to GND is recommended for best circuit response. LDO regulator power input. Connect to IN to power from a common input supply with the load switch, in which case, bypass with a 1F ceramic capacitor connected between this pin and ground. Alternatively, this pin may be powered from the load switch output by connecting IN_REG to OUT; a 1F or greater ceramic capacitor should be placed between the OUT pin and ground for this application LDO regulator output. Connect a 1F or larger capacitor from VREG to GND for best operating performance. IC ground pin. Current limit set input. Connect a resistor from SET to ground to program current limit set point for the load switch. Or leave open for 150mA default current limit level. Fault flag, open drain output. Pull to a logic high level through an external resistor for normal operation. Pulled low when fault is present. Leave open if unused. Enable input for load switch and LDO regulator. AAT4702 -1: Active low; pull to a logic low level to enable. AAT4702 -2: Active high; pull to a logic high level to enable. Input to the P-channel MOSFET source. Connect a 1F capacitor from IN to GND. Pin Configuration FTDFN22-8L (Top View) OUT IN_REG VREG GND 2 1 8 2 7 3 6 4 5 IN ON (ON) FLT SET www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Absolute Maximum Ratings1 TA = 25C unless otherwise noted. Symbol VIN, FAULT VON VOUT IOUT VESD TJ TLEAD Description Value IN, IN_REG, FAULT to GND ON to GND OUT to GND Maximum Output Current2 ESD Rating, HBM Maximum Junction Operating temperature Maximum Soldering Temperature (at leads, 10 sec) Units -0.3 to 6 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 Internally Limited 4000 -40 to +150 300 V A V O C Thermal Information3 Symbol JA PD Description Value Thermal Resistance Maximum Power Dissipation4 (TA = 25oC) 116.3 860 Units C/W mW O 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Based on long-term current density limitations. 3. Mounted on 1oz. copper clad FR4 material printed circuit board. 4. Derate 8.6mW/C above 25C. 4702.2009.02.1.2 www.analogictech.com 3 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Electrical Characteristics1 VIN=3.6V;TA = -40oC to 85oC unless otherwise noted. Typical values are at TA = 25oC. Symbol Description Conditions General VIN(SW) Input Voltage Range VIN(REG) Input Voltage Range Load Switch Section Stable Output For VOUT Within Regulation Tolerance VIN = 5V, ON = 0V, IOUT = 0 ON = IN = 5.5V, VOUT = 0 Operation Quiescent Current Shutdown Supply Current ISD(OFF) Load Switch IQ RDS(ON) VOUT = 5V, TA = 25C VOUT = 3.6V, TA = 25C VOUT = 2.4V, TA = 25C ON = VIN Rising edge; RSET = open PMOS On-Resistance Switch Off-Leakage ID(OFF) Current Limit ILIM RSET_INT Current Limit Internal Set Resistor Under-Voltage Lockout Threshold VUVLO Under-Voltage Lockout Hysteresis VUVLO_HYS LDO Regulator DC Output Voltage VOUT Output Current IOUT Short-Circuit Current ISC VOUT/ Line Regulation VOUT*VIN Min 2.4 2.4 VOUT + VDO 15 180 220 270 100 Rising edge VIN = 3.6V, IOUT = 10mA VOUT = 1.8V VOUT < 0.4V 1.764 Load Regulation VDO RDS(REG) PSRR TC Logic VEN(L) Dropout Voltage Regulator Pass Element On-Resistance Power Supply Rejection Ratio Output Voltage Temperature Coefficient 150 50 1.8 0.2 1.8 Max 5.5 5.5 5.5 30 1 280 320 360 1 200 2.4 IOUT = 1mA to 100mA, VOUT = 1.8V, TA = 25C IOUT = 100mA, VOUT = 1.8V VIN_REG = 3.6V 100Hz ON Input High Voltage IEN tAUTO tBLANK tRESP tON tOFF TSD THYS ON Input Leakage Auto-Restart Time Over-Current Blanking Time Current Limit Response Time Load Switch Turn On Time Load Switch Turn Off Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis VIN = 5V VIN = 5V; RO = 10; CO = 1F VIN = 5V; RO = 10; CO = 1F m A mA k V V 0.4 %/V 1.0 1.65 % 300 3.0 50 80 mV dB PPM/C 2.0 2.4 20 2 % A A 0.14 0.4 VEN(H) V V mA mA ON Input Low Voltage 2.4V < VIN 4.2V 4.2V < VIN < 5.5V VEN = 5.5V or 0V Units 1.836 100 350 VIN = 4.0 to 5.5V, TA = 25C VOUT/VOUT Typ V V 0.5 40 5 0.4 18 3 140 20 2.0 80 10 35 10 A ms ms s s s C C 1. The AAT4702 is guaranteed to meet performance over the -40oC to +85oC operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Typical Characteristics-General Unless otherwise noted, VIN= 3.6V, CIN = 1F, COUT = 1F, COUT-LDO = 1F ,TA = 25C. Quiescent Current vs. Temperature Quiescent Current vs. Input Voltage (Load Switch + LDO) (Load Switch + LDO) 30 Quiescent Current (A) 30 25 IQ (A) 20 15 10 VIN = 5.5V VIN = 4.2V VIN = 3.3V 5 0 -40 -15 10 35 60 85 25 20 15 10 5 0 0.5 Temperature (C) 1.5 2.5 3.5 4.5 5.5 Input Voltage (V) VEN(H) and VEN(L) vs. Input Voltage VEN(H) and VEN(L) (V) 2.4 1.9 1.4 0.9 VEN(H) VEN(L) 0.4 2 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) 4702.2009.02.1.2 www.analogictech.com 5 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Typical Characteristics-Load Switch Unless otherwise noted, VIN= 3.6V, CIN = 1F, COUT = 1F, COUT-LDO = 1F ,TA = 25C. VUVLO vs. Temperature Switch Off-Leakage Current vs. Temperature (Rising and Falling) 0.05 2 VIN = 5.5V VIN = 3.6V VIN = 2.4V 1.9 0.04 1.8 ID(OFF) (A) VUVLO (V) 1.7 1.6 1.5 1.4 0.03 0.02 1.3 1.2 0.01 Rising Edge Falling Edge 1.1 1 -40 -15 10 35 60 0 -40 85 -15 10 Temperature (C) 60 85 Temperature (C) RDS(ON) vs. Input Voltage RDS(ON) vs. Temperature 280 380 IOUT = 100mA IOUT = 50mA 340 RDS(ON) (m) 260 RDS(ON) (m) 35 240 220 200 180 300 260 220 180 VIN = 2.4V VIN = 3.6V VIN = 5.5V 140 160 2 2.5 3 3.5 4 4.5 5 100 -40 5.5 -15 10 Input Voltage (V) 35 60 85 Temperature (C) Current Limit vs. Output Voltage RSET vs. ILIM (RSET = Open) 200 1000 180 160 RSET (k) ILIM (mA) 140 120 100 80 60 100 10 40 20 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 1 150 Output Voltage (V) 6 250 350 450 550 650 750 850 950 1050 1150 1250 ILIM (mA) www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Typical Characteristics-Load Switch Unless otherwise noted, VIN= 3.6V, CIN = 1F, COUT = 1F, COUT-LDO = 1F ,TA = 25C. TBLANK Response TAUTO Response (VIN = 4V; RSET = Open) (VIN = 4V; RSET = Open) VDRIVE (5V/div) VDRIVE (5V/div) VOUT (5V/div) VOUT (5V/div) IOUT (200mA/div) IOUT (200mA/div) FLT (5V/div) FLT (5V/div) Time (4ms/div) Time (10ms/div) TON Response TOFF Response (VIN = 5V; RL = 40; CL = 0.1F) (VIN = 5V; RL = 40; CL = 1F) ON (5V/div) ON (5V/div) VOUT (2V/div) VOUT (2V/div) IOUT (50mA/div) IOUT (50mA/div) Time (40s/div) 4702.2009.02.1.2 Time (40s/div) www.analogictech.com 7 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Typical Characteristics-LDO Regulator Unless otherwise noted, VIN= 3.6V, CIN = 1F, COUT = 1F, COUT-LDO = 1F ,TA = 25C. Output Voltage vs. Output Current Output Voltage vs. Output Current 2 1.8 1.81 Output Voltage (V) Output Voltage (V) 1.82 1.8 1.79 1.78 1.77 1.76 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 1.75 0 20 40 60 80 0 100 100 150 200 Output Current (mA) 1.8 1.81 Output Voltage (V) Output Voltage (V) 1.82 1.7 1.6 IOUT = 1mA IOUT = 10mA IOUT = 40mA IOUT = 100mA 1.9 2.1 400 450 500 2.3 1.8 1.79 1.78 IOUT = 1mA IOUT = 10mA IOUT = 40mA IOUT = 100mA 1.77 1.76 1.3 1.7 350 Output Voltage vs. Input Voltage 1.9 1.4 300 Output Current (mA) Output Voltage vs. Input Voltage 1.5 250 2.5 1.75 2.5 Input Voltage (V) 3 3.5 4 4.5 5 5.5 Input Voltage (V) Line Transient Response Dropout Voltage vs. Output Current (VIN = 4V->5V->4V; IOUT = 1mA) Dropout Voltage (mV) 350 300 VIN (2V/div) 250 200 VOUT (AC Coupled) (200mV/div) 150 100 IOUT (10mA/div) 50 0 0 20 40 60 80 100 Output Current (mA) 8 Time (1ms/div) www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Typical Characteristics-LDO Regulator Unless otherwise noted, VIN= 3.6V, CIN = 1F, COUT = 1F, COUT-LDO = 1F ,TA = 25C. Line Transient Response Line Transient Response (VIN = 4V->5V->4V; IOUT = 20mA) (VIN = 4V->5V->4V; IOUT = 100mA) VIN (2V/div) VIN (2V/div) VOUT (AC Coupled) (200mV/div) VOUT (AC Coupled) (200mV/div) IOUT (20mA/div) IOUT (50mA/div) Time (1ms/div) Time (1ms/div) Load Transient Response Load Transient Response (VIN = 4V; IOUT = 1mA-50mA) (VIN = 4V; IOUT = 1mA-100mA) VOUT (AC Coupled) (200mV/div) VOUT (AC Coupled) (200mV/div) IOUT (50mA/div) IOUT (50mA/div) Time (400s/div) Time (400s/div) Power-Up with 1mA Load Power-Up with 100mA Load ON (2V/div) ON (2V/div) VOUT (1V/div) VOUT (1V/div) Time (200s/div) 4702.2009.02.1.2 Time (200s/div) www.analogictech.com 9 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Functional Block Diagram Reverse Blocking IN OUT Timer ON / ON Control Current Set Over-Temperature Protection SET FAULT 1.2V Reference 10ms Delay IN_REG VREG GND Functional Description The AAT4702 is an auto-restarting current limiting load switch with an integrated low dropout linear voltage regulator. The combined function of this device serves to protect system loads or peripheral circuits from overcurrent conditions while simultaneously supplying an independent regulated voltage for the system. Current Limiting Load Switch The AAT4702 load switch provides an auto-restarting, reverse current blocking, programmable current limiting and shutdown function. If an applied load exceeds the programmed current limit level, the load switch pass element will be turned off to isolate the input source from 10 the output and discharge the applied load to ground via an internal NMOS switch and a typical 100 resistor. The default current limit (ILIM) set point is 150mA with a 50mA tolerance when the SET pin is left open (no external resistor connected). The device may be user programmed to a higher current limit level up to 1A via an external resistor placed between the SET pin and ground. When under an output over-current shutdown event, the AAT4702 has an auto-restart output polling function that will wake up and re-enable the device every 40ms to check for the continued existence of an over-current condition. If the over-current fault condition remains, the AAT4702 will remain in the shutdown state with both the load switch and LDO regulator output pulled low to www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator ground. When the over-current condition is removed, the AAT4702 will automatically resume normal operation. The internal load switch controller provides a fault flag function to alert a system controller to any over current or temperature event. The fault flag output consists of an open drain NMOS switch that should be pulled to a logic high level externally through a 10k or greater value resistor. The fault flag has a 5ms blanking time feature to guard against reporting false fault conditions, such events could happen during normal circuit start-up. If the fault flag function is not required, the FLT pin may be left unconnected. When operating within the limits set by the default or user programmed current limit level, the device overtemperature protection will monitor the internal die temperature. If the internal die temperature exceeds 140C, the thermal protection circuit will shut down the load switch to protect the loaded device and the system supply source. The AAT4702 load switch and LDO regulator are enabled and disabled through common enable signal at the ON (ON) pin. The AAT4702 provides options for both active low (default) and/or active high operation; refer to the Ordering Information table to select the desired enable polarity. If the device is operated in an always-on state, the enable function may be terminated to GND or IN respective to which active low or high option is selected. The AAT4702 load switch has an under-voltage lockout (UVLO) function, which senses the voltage of the IN pin. Once VIN > VUVLO rising edge (typical 1.8V), the AAT4702 will start to operate. For the LDO regulator input IN_REG pin, there is no UVLO. Low Dropout Linear Regulator The AAT4702 LDO linear regulator section has an independent input pin allowing the regulator to be powered by the load switch output or directly from an input supply. When the enable pin switches to an active state, the LDO regulator output will typically start up and stabilize regulation within 1ms after the load switch. The LDO regulator output is designed and tested to maintain voltage regulation accuracy within a 2% toler- 4702.2009.02.1.2 ance. Voltage regulation accuracy is maintained for input voltage ranges from 5.5V down to a minimum input level (VIN_MIN) which is defined by the factory trimmed output voltage level (VOUT) plus the specified regulator dropout voltage level (VDO), by following the formula: VIN_MIN = VOUT + VDO Where: VIN_MIN = Minimum input voltage applied to the IN_REG pin to maintain regulation VOUT = Factory set LDO regulator output as measured at the VREG pin VDO = Specified LDO regulator dropout voltage Should the LDO regulator input supply fall below the required VIN_MIN level, the output is designed to track the input supply minus a nominal voltage drop across the regulator's high-side P-channel MOSFET caused by the device's on resistance. The regulator is designed to maintain a stable linear output level of 1.8V for an input supply level down to 2.4V at the specified load current level of 100mA. During LDO regulator shutdown, the VREG output is internally connected to ground via a series resistor and a low-side NMOS switch which have a combined impedance of 100. The LDO regulator has over-temperature and short-circuit protection independent to the load switch for comprehensive device protection. Since the system enable is common to both the LDO regulator and load switch, the LDO regulator will shut down in the event of a fault occurring on the load switch output. For the case of LDO regulator shut down via a load switch fault, the LDO regulator automatically restarts along with the load switch auto-restart system with a 1ms delay. When the LDO regulator is shut down by either the enable function or a fault on the load switch output, the regulator output load will be discharged through the internal active output pull-down circuit. The AAT4702 LDO regulator has high power supply ripple rejection (PSRR) in addition to fast load and line transient response characteristics. The LDO regulator output has been specifically optimized to function with low cost, low-ESR ceramic capacitors. www.analogictech.com 11 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Application Information Setting the Load Switch Current Limit With no external resistor at the SET pin, the default current limit is 150mA typically set by the internal 50k resister. The current limit function is triggered when the load current reaches 150mA, the load switch and LDO output voltages are shut down; the AAT4702 would restart to check if the over-current condition is removed every 40ms. As illustrated in the "Current Limit ILIM vs. Output Voltage" curve, the current limit level is kept lower when the output voltage drops; this is helpful to minimize the power dissipation at the load switch to provide safer operation at over-current or output short-circuit condition. If a higher current limit is desired, an external resistor could be placed at the SET pin. To determine RSET, multiply the maximum current drawn by the load by 1.33 (typical ILIM = minimum ILIM/0.75); this is the typical current limit value. Next, refer to the "RSET vs. ILIM" curve and find the RSET that corresponds to the typical current limit value. The maximum current is derived by multiplying the typical current for the chosen RSET in the chart by 1.25. Some resistor values are listed in Table 1. RSET (k) Current Limit Typ (mA) Current Limit Min (mA) Current Limit Max (mA) 205.1 80.9 49.6 39.6 32.2 27.6 24 20.8 17.6 13.3 10.8 8.82 7.88 6.87 6.17 5.54 200 250 300 350 400 450 500 550 600 700 800 900 1000 1100 1200 1300 150 188 225 263 300 338 375 413 450 525 600 675 750 825 900 975 250 313 375 438 500 563 625 688 750 875 1000 1125 1250 1375 1500 1625 Table 1: Current Limit vs. RSET Values. 12 Example: A USB port requires 500mA. 500mA multiplied by 1.33 is 665mA. From the "RSET vs. ILIM" curve, RSET should be less than 16.5k. 14.9k is a standard value that is a little less than 16.5k but very close. The chart reads approximately 700mA as a typical ILIM value for 14.9k. Multiplying 700mA by 0.75 and 1.25 shows that the AAT4702 load switch will limit the load current to greater than 525mA but less than 875mA. Load Switch Operation in Current Limit and Thermal Protection When a heavy load is applied to the output of the AAT4702 load switch output, the current limit circuit is triggered when the load current reaches the value of ILIM determined by RSET. See Figure 1 for over-current operation and fault recovery. Since the load demands more current than ILIM, the voltage at the output drops. When the output voltage drops, the load current is folded back to a lower level. When the overload condition continues for a period longer than the over-current blanking time tBLANK, the output will be turned off and discharged through the internal N-channel MOSFET and resistor. After TAUTO timeout 40ms, the AAT4702 turns on the load switch output to check if the overload condition is removed. If the overload still exists, the output turns off again after tBLANK timeout. The AAT4702 load switch and LDO will continue to cycle on and off until the overload condition is removed. When the die temperature exceeds the over-temperature limit, the AAT4702 will shutdown until it has cooled sufficiently, at which point it will start up again. Enable Input The AAT4702 features a load switch and LDO common enable / disable function. This ON (ON) pin is compatible with CMOS logic. Active high or active low options are available (see Ordering Information). In many systems, power planes are controlled by integrated circuits which run at lower voltages than the power plane itself. The enable input ON (ON) of the AAT4702 has low and high threshold voltages that accommodate this condition, which could be found in "VEN(H) and VEN(L) vs. Input Voltage" curve. The threshold voltages are compatible with 5V TTL and 2.4V to 5V CMOS. When enable is active, the load switch starts up, and the LDO starts up after 1ms. When it is disabled, the device shuts down and the LDO output capacitor is discharged through the internal N-channel MOSFET and 100 resistor; the load switch is also reverse blocked. www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Normal Operation Fault Recovers Over-Current Protection ILIM IOUT <150mA (default) IOUT<150mA (default) IOUT IOUT =0 IOUT =0 VOUT recovers VOUT=VIN-IOUT RDS(ON ) Load Switch Disabled (OUT pulled to GND) VOUT VOUT=0 VVREG=1.8V VREG V VREG=1.8V LDO Disabled (VREG pulled to GND) VVREG=0 VVREG=0 FLT=high FLT FLT=low ON=high ON ON=low tBLANK tBLANK tAUTO tBLANK tAUTO Figure 1: AAT4702 Device Output and Logic Timing Diagram for a Fault Condition and Fault Recovery. Reverse Voltage Output Capacitor The AAT4702 load switch is designed to control the current flowing from IN to OUT. If a voltage applied to OUT is greater than the voltage on IN, large current may flow if the enable is active. This could cause damage to the AAT4702. The ON (ON) pin can be pulled to low to disable the device and prevent current flow from OUT to IN, as the AAT4702 load switch could be reverse blocked when ON (ON) is disabled. A 1F or larger ceramic capacitor COUT1 is typically recommended for the load switch output OUT pin in most applications. Input Capacitor A 1F or larger ceramic capacitor is typically recommended for CIN in most applications. CIN should be located as closely to the device IN pin as practically possible. CIN value greater than 1F will offer superior input line transient response and will assist in maximizing the power supply ripple rejection. Ceramic capacitors are recommended for CIN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources such as batteries in portable devices. 4702.2009.02.1.2 For proper load voltage regulation and operational stability, a capacitor is required between pins VREG and GND. The COUT2 capacitor connection to the LDO regulator output VREG pin and GND pin should be made as direct as practically possible for maximum device performance. The AAT4702 LDO has been specially designed to function with very low ESR ceramic capacitors. Although the device is intended to operate with these low ESR capacitors, it is stable over a wide range of capacitor ESR, thus it will also work with some higher ESR tantalum or aluminum electrolytic capacitors. However, for best performance, ceramic capacitors are recommended. The value of COUT2 typically ranges from 0.47F to 10F; however, 1F is sufficient for most operating conditions. If large output current steps are required by an application, then an increased value for COUT2 should be consid- www.analogictech.com 13 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator ered. The amount of capacitance needed can be calculated from the step size of the change in output load current expected and the voltage excursion that the load can tolerate. The total LDO output capacitance required can be calculated using the following formula: COUT2 = I * 15F V Where: I = maximum step in output current V = maximum excursion in voltage that the load can tolerate Note that use of this equation results in capacitor values approximately two to four times the typical value needed for an AAT4702 at room temperature. The increased capacitor value is recommended if tight LDO output tolerance must be maintained over extreme operating conditions and maximum operational temperature excursions. If tantalum or aluminum electrolytic capacitors are used, the capacitor value should be increased to compensate for the substantial ESR inherent to these capacitor types. Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT4702. Ceramic capacitors offer many advantages over the tantalum and aluminum electrolytic counterparts. A ceramic capacitors typically has very low ESR 10m, is lower cost, has a smaller PCB footprint, and is non-polarized. Line and load transient response of the LDO regulator is improved by using low-ESR ceramic capacitors. Since ceramic capacitors are non-polarized, they are less prone to damage if incorrectly connected. Equivalent series resistance (ESR) is a very important characteristic to consider when selecting a capacitor. ESR is the internal series resistance associated with a capacitor, which includes lead resistance, internal connections, capacitor size and area, material composition, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. Ceramic capacitors less than 0.1F are typically made from NPO or C0G materials. NPO and C0G materials are 14 typically tight tolerance and very stable over temperature. Larger capacitor values are typically composed of X7R, X5R, Y5U, and Z5V dielectric materials. Large ceramic capacitors, typically greater than 2.2F, are often available in low-cost Y5V and Z5U dielectrics. These two materials types are not recommended for use with LDO regulators since the capacitor tolerance can vary more than 50% over the operating temperature range of the device. A 2.2F Y5V capacitor could be reduced to 1F over the full operating temperature range. This can cause problems for circuit operation and stability. X7R and X5R dielectrics are much more desired. The temperature tolerance of X7R dielectric is better than 15%. Capacitor area is another contributor to ESR. Capacitors that are physically large in size will have a lower ESR when compared to a smaller sized capacitor of equivalent material and capacitor value. These larger device can also improve circuit transient response when compared to an equal value capacitor in a smaller package size. Consult capacitor vendor datasheets carefully when selecting capacitors for use with LDO regulators. LDO Short-Circuit Protection and Thermal Protection The AAT4702 LDO regulator is protected by both current limit and over-temperature protection circuitry. The internal short-circuit limit is designed to active when the output load demand exceeds the maximum rated output current. If a short-circuit condition were to continually draw more than the current limit threshold, the LDO regulator's output voltage will drop to a level necessary to supply the current demanded by the load. Under short-circuit or other over-current operating conditions, the output voltage will drop and the AAT4702 die temperature will rapidly increase. Once the device's power dissipation capacity has been exceeded and the internal die temperature reaches approximately 140C at the over-current condition, the LDO thermal protection circuit will actively turn off the LDO regulator output pass element to prevent the possibility of over-temperature damage. The LDO regulator output will remain in a shutdown state until the internal die temperature falls back below the 140C trip point. The interaction between the short-circuit and thermal protection allows the LDO regulator to withstand indefinite short-circuit without sustaining permanent damage. www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator LDO No-Load Stability PD(MAX) = (VIN - VOUT) * IOUT-LDO(MAX) + I2OUT-SW(MAX) * RDS(ON) + VIN * IQ The AAT4702 LDO regulator is designed to maintain output voltage regulation and stability under operational no-load conditions. This is an important characteristic for applications where the output current may drop to zero. An output capacitor is required for stability under noload operating conditions. Refer to the "Output Capacitor" section of this document for recommended typical output capacitor values. Where: VIN = LDO input voltage VOUT = LDO output voltage IOUT-LDO(MAX) = LDO maximum output current IOUT-SW(MAX) = Load switch maximum output current RDS(ON) = Load switch on-state resistance, 320m maximum at VIN=3.6V IQ = Operation Quiescent Current, maximum 30A Thermal Considerations and High Output Current Applications For example, if VIN = 5V, VOUT = 1.8V, IOUT-SW = 200mA and TA = 85oC, then IOUT-LDO(MAX) = 103.5mA. The load switch output short-circuit protection threshold could be set between 150mA to 200mA. If the LDO output load current were to exceed 103.5mA or the ambient temperature were to increase, the internal die temperature would increase. If the conditions remained constant and the short-circuit protection did not active, there would be a potential damage hazard to the LDO regulator since the thermal protection circuit would only activate after a short-circuit event or over-current occurred on the LDO regulator output. One solution is to supply the LDO input from the load switch OUT pin; when the internal die temperature reaches the load switch thermal protection point, the load switch output will be disconnected. The AAT4702 is designed to deliver a continuous output load current of 1A by the load switch, and 100mA by the LDO regulator under normal operating conditions. The limiting characteristics for the maximum output load safe operating area are essentially package power dissipation and the internal preset thermal limit of the device. In order to obtain high operating currents, careful device layout and circuit operating conditions need to be taken into account. The following discussions will assume the device is mounted on a printed circuit board utilizing the minimum recommended footprint and the printed circuit board is 0.062-inch thick FR4 material with one ounce copper. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equation: PD(MAX) = TJ(MAX) - TA JA Constants for the AAT4702 are TJ(MAX), the maximum junction temperature for the device which is 125C, and the package thermal resistance from junction to ambient JA = 116.3C/W for the FTDFN22-8L. Typically, maximum conditions are calculated at the maximum operating ambient temperature where TA = 85C. Given TA = 85C, from the above formula, the maximum FTDFN228L package power dissipation is 344mW at TA = 85C. At TA = 25C, the maximum package power dissipation is 860mW. The maximum continuous output current for the AAT4702 is a function of the package power dissipation and the input-to-output voltage drop across the LDO regulator and the load switch power consumption. Refer to the following equation for the total power dissipation: 4702.2009.02.1.2 High Peak Output Current Applications Some applications require the LDO regulator or the load switch to operate at continuous nominal levels with short duration, high-current peaks. The duty cycles for both output current levels must be taken into account. To do so, one would first need to calculate the power dissipation at the nominal continuous level, then factor in the addition power dissipation due to the short duration, high-current peaks. For example, a 1.8V system using an AAT4702 operates at a continuous 80mA LDO load current level and has short 150mA current peaks, the load switch load current is 200mA. The LDO current peak occurs for 378s out of a 4.61ms period. It will be assumed the input voltage is 5.0V. First, the current duty cycle percentage must be calculated: Peak current duty cycle (%): = 100 * 378s/4.61ms = 8.2% www.analogictech.com 15 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator The LDO regulator will be under 80mA for 91.8% of the 4.61ms period and have 150mA peaks occurring for 8.2% of the time. Next, the continuous nominal power dissipation for the 80mA load should be determined, and then multiplied by the duty cycle to calculate the actual power dissipation over time. PD(MAX) = (VIN - VOUT) * IOUT-LDO(MAX) + I2OUT-SW(MAX) * RDS(ON) + VIN * IQ PD(80mA) = (5.0V - 1.8V) * 80mA = 256mW PD(91.8%-80mA) = 0.918 * PD(80mA) = 0.918 * 256mW = 235.01mW The power dissipation for an 80mA LDO load occurring for 91.8% of the duty cycle will be 235.01mW. Now the power dissipation for the 8.2% of the duty cycle at the 150mA LDO load can be calculated: PD(150mA) = (5.0V - 1.8V) * 150mA = 480mW PD(8.2%-150mA) = 0.082 * PD(150mA) = 0.082 * 480mW = 39.36mW The power dissipation for a 150mA LDO load occurring for 8.2% of the duty cycle will be 39.36mW. The last portion is the load switch 200mA power dissipation: PD(200mA) = I2OUT-SW(MAX) * RDS(ON) = (200mA)2 * 320m = 12.8mW 16 The power dissipation of 200mA load switch current is 12.8mW. Finally, the three power dissipation levels can be summed to determine the total true power dissipation under the varied load: PD(total) = PD(91.8%-80mA) + PD(8.2%-150mA) + PD(200mA) = 235.01mW + 39.36mW +12.8mW = 287.17mW The maximum power dissipation for the FTDFN22-8L operating at an ambient temperature of 85C is 344mW. The device in this example will have a total power dissipation of 287.17mW. This is within the thermal limits for safe operation of the device. Printed Circuit Board Layout Recommendations In order to obtain the maximum performance from the AAT4702, very careful attention must be considered in regard to the printed circuit board layout. If grounding connections are not properly made, power supply ripple rejection and LDO regulator transient response can be compromised. The load switch and LDO external capacitor CIN and COUT should be connected as directly to the ground pin. For maximum performance with the AAT4702, the ground pin connection should then be made directly back to the ground or common of the source power supply. If a direct ground return path is not possible due to printed circuit board layout limitations, the LDO ground pin should then be connected to the common ground plane in the application layout. www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Application Circuits INPUT IN OUT OUTPUT AAT4702 1F N/C IN_REG SET ON / ON ENABLE FLT FAULT FLAG LDO REG OUTPUT VREG GND 1F 1F Figure 2: AAT4702 Application Circuit with the Load Switch and LDO Regulator Powered from a Common Input. INPUT IN OUT OUTPUT AAT4702 1F ENABLE IN_REG VREG ON/ON 10k FLT SET LDO REG OUTPUT FAULT FLAG GND 1F 1F RSET Figure 3: AAT4702 Application Circuit with User Set (RSET) Current Limit and Fault Flag Pull-Up Resistor. 4702.2009.02.1.2 www.analogictech.com 17 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Evaluation Board Schematic U1 R2 7.5K JP4 1 5 1 2 JP3 7 8 VIN C1 1F GND FLT VREG C4 DNP 4 C3 1F 2 6 R1 10K SET ON (ON) IN_REG IN OUT 3 VOUT_LDO 2 C2 1F 1 VOUT 1 2 3 AAT4702 (FTDFN22-8) JP1 JP2 1 2 3 Figure 4: AAT4702 Evaluation Board Schematic. Evaluation Board Layout Figure 5: AAT4702 Evaluation Board Top Layer (not to scale). 18 Figure 6: AAT4702 Evaluation Board Bottom Layer (not to scale). www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Component Part Number Description Manufacturer U1 C1, C2, C3 C4 R1 R2 JP1, JP2 JP3, JP4 AAT4702 GRM188R61A105KA61 DNP Chip Resistor Chip Resistor Connector Connector Shunt PCB Auto Restarting Current Limiting Load Switch with LDO regulator SMD, Cap ceramic 1F 0603 X5R 10V 10% DNP, Do Not Place SMD, 10k, 5%, 150mW, 0603 SMD, 7.5k, 5%, 150mW, 0603 Header 3 pins, pitch 75mil Header 2 pins, pitch 75mil Shunt for connector AAT4702 Evaluation board PCB AnalogicTech Murata Vishay Vishay Any Any Any AnalogicTech Table 2: AAT4702 Evaluation Board Bill of Materials (BOM). 4702.2009.02.1.2 www.analogictech.com 19 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Ordering Information Package Voltage Regulator Output Enable Marking1 Part Number (Tape and Reel)2 FTDFN22-8L FTDFN22-8L 1.8V 1.8V Active Low Active High 7CXYY AAT4702IXS-1-T1 AAT4702IXS-2-T1 All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/about/quality.aspx. Package Information FTDFN22-8L 0.400 0.050 Detail "A" 2.000 0.050 Index Area Bottom View 2.000 0.050 Top View + 0.100 - 0.000 Pin 1 Identification 0.250 0.050 Side View 0.450 0.050 0.000 0.230 0.050 0.750 0.050 0.500 0.050 Detail "A" All dimensions in millimeters. 1. XYY= assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 20 www.analogictech.com 4702.2009.02.1.2 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 (c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 4702.2009.02.1.2 www.analogictech.com 21 PRODUCT DATASHEET AAT4702 SmartSwitchTM Auto-Restarting Current Limiting Load Switch with LDO Regulator Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 (c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 22 www.analogictech.com 4702.2009.02.1.2