APS1056 Fast Transient 600mA Step-Down Converter General Description Features The APS1056 SwitchReg is a member of AnalogicTech's Total Power Management IC™ (TPMIC™) product family. It is a 1.4MHz stepdown converter with an input voltage range of 2.7V to 5.5V and output voltage as low as 0.6V. It is optimized to react quickly to a load variation. • • • • • • • • • • • • • • VIN Range: 2.7V to 5.5V VOUT Fixed or Adjustable from 0.6V to VIN 27µA No Load Quiescent Current Up to 98% Efficiency 600mA Max Output Current 1.4MHz Switching Frequency 120µs Soft Start Fast Load Transient Over-Temperature Protection Current Limit Protection 100% Duty Cycle Low-Dropout Operation <1µA Shutdown Current SOT23-5 Package Temperature Range: -40°C to +85°C Preliminary Information The APS1056 is available in fixed voltage versions with internal feedback and a programmable version with external feedback resistors. It can deliver 600mA of load current while maintaining a low 27µA no load quiescent current. The 1.4MHz switching frequency minimizes the size of external components while keeping switching losses low. SwitchReg™ The APS1056 is designed to maintain high efficiency throughout the operating range, which is critical for portable applications. Applications The APS1056 is available in a Pb-free SOT23-5 package and is rated over the -40°C to +85°C temperature range. • • • • • • Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core / IO Power PDAs and Handheld Computers USB Devices Typical Application (Fixed Output Voltage) VIN VO U1 APS1056 VIN C2 4.7µF EN GND APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) L1 LX 4.7µH OUT C1 4.7µF 1 APS1056 Fast Transient 600mA Step-Down Converter Pin Descriptions Pin # Symbol 1 2 3 4 VIN GND EN OUT 5 LX Function Input supply voltage for the converter. Ground pin. Connect to the output and input capacitor return. Enable pin. Feedback input pin. This pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high- and low-side MOSFETs. Pin Configuration SOT23-5 (Top View) 2 VIN 1 GND 2 EN 3 5 LX 4 OUT (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VOUT VEN TJ TLEAD Description Input Voltage GND LX to GND OUT to GND EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -40 to 150 300 V V V V °C °C Value Units 667 150 mW °C/W Thermal Information Symbol PD θJA Description Maximum Power Dissipation Thermal Resistance2 2, 3 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. Mounted on an FR4 board. 3. Derate 6.67mW/°C above 25°C. APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 3 APS1056 Fast Transient 600mA Step-Down Converter Electrical Characteristics1 TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V. Symbol Description Conditions Min Step-Down Converter VIN Input Voltage VUVLO UVLO Threshold VOUT Output Voltage Tolerance VOUT Output Voltage Range IQ ISHDN ILIM RDS(ON)H RDS(ON)L ILXLEAK ∆VLinereg Quiescent Current Shutdown Current P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance LX Leakage Current Line Regulation VOUT Out Threshold Voltage Accuracy IOUT ROUT Out Leakage Current Out Impedance TS Start-Up Time FOSC TSD THYS Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis VEN(L) VEN(H) IEN Enable Threshold Low Enable Threshold High Input Low Current Typ Max Units 5.5 2.7 V V mV V -3.5 +3.5 % 0.6 VIN V 70 µA 1.0 µA mA Ω Ω 1 µA 2.7 VIN Rising Hysteresis VIN Falling IOUT = 0 to 600mA, VIN = 2.7V to 5.5V 100 1.8 No Load, 0.6V Adjustable Version EN = AGND = PGND 27 600 0.45 0.40 VIN = 5.5V, VLX = 0 to VIN, EN = GND VIN = 2.7V to 5.5V 0.6V Output, No Load TA = 25°C 0.6V Output >0.6V Output From Enable to Output Regulation TA = 25°C 0.1 591 600 %/V 609 mV 0.2 µA kΩ 250 150 1.0 1.4 140 15 µs 2.0 MHz °C °C 0.6 V V µA EN VIN = VOUT = 5.5V 1.4 -1.0 1.0 1. The APS1056 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Typical Characteristics Efficiency vs. Load DC Regulation (VOUT = 1.8V; L = 4.7µ µH) (VOUT = 1.8V) 1.0 100 Efficiency (%) 80 Output Error (%) VIN = 2.7V 90 VIN = 4.2V VIN = 3.6V 70 60 0.5 VIN = 4.2V 0.0 VIN = 3.6V -0.5 VIN = 2.7V 50 0.1 1 10 100 -1.0 0.1 1000 1 10 100 Output Current (mA) Output Current (mA) Efficiency vs. Load DC Regulation (VOUT = 2.5V; L = 6.8µ µH) (VOUT = 2.5V) 100 1.0 VIN = 2.7V VIN = 4.2V Output Error (%) 90 Efficiency (%) 1000 VIN = 5.0V 80 VIN = 4.2V 70 VIN = 3.6V 60 0.5 VIN = 5.0V 0.0 VIN = 3.6V -0.5 VIN = 3.0V 50 0.1 -1.0 1 10 100 0.1 1000 1 Output Current (mA) 1000 DC Regulation (VOUT = 3.3V; L = 6.8µ µH) (VOUT = 3.3V; L = 6.8µH) 100 1.0 VIN = 3.6V VIN = 5.0V Output Error (%) 90 Efficiency (%) 100 Output Current (mA) Efficiency vs. Load VIN = 4.2V 80 VIN = 5.0V 70 60 50 0.1 10 0.5 VIN = 4.2V 0.0 -0.5 VIN = 3.6V -1.0 1 10 100 Output Current (mA) APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 1000 0.1 1 10 100 1000 Output Current (mA) 5 APS1056 Fast Transient 600mA Step-Down Converter Typical Characteristics Line Regulation Soft Start (VOUT = 1.8V) 5.0 0.40 1.6 0.30 1.2 0.20 2.0 1.0 1.0 0.8 VEN VO 0.0 0.6 -1.0 0.4 -2.0 0.2 IL -3.0 0.0 -4.0 -0.2 -5.0 -0.4 Accuracy (%) 1.4 3.0 4.0 Inductor Current (bottom) (A) Enable and Output Voltage (top) (V) (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) IOUT = 10mA 0.10 0.00 -0.10 IOUT = 1mA IOUT = 400mA -0.20 -0.30 -0.40 2.5 3.0 3.5 µs/div) Time (100µ 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) Output Voltage Error vs. Temperature Switching Frequency vs. Temperature (VIN = 3.6V; VO = 1.8V; IOUT = 400mA) (VIN = 3.6V; VOUT = 1.8V) 2.0 15.0 9.0 1.0 Variation (%) Output Error (%) 12.0 0.0 -1.0 6.0 3.0 0.0 -3.0 -6.0 -9.0 -12.0 -2.0 -40 -20 0 20 40 60 80 -15.0 -40 100 -20 0 Temperature (°°C) 60 80 100 No Load Quiescent Current vs. Input Voltage 2.0 50 1.0 Supply Current (µ µA) Frequency Variation (%) 40 Temperature (°°C) Frequency vs. Input Voltage VOUT = 1.8V 0.0 -1.0 VOUT = 2.5V VOUT = 3.3V -2.0 -3.0 45 40 35 25°C 85°C 30 25 20 15 -40°C 10 -4.0 2.7 3.1 3.5 3.9 4.3 Input Voltage (V) 6 20 4.7 5.1 5.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Typical Characteristics P-Channel RDS(ON) vs. Input Voltage 750 750 700 700 650 120°C 650 100°C RDS(ON) (mΩ Ω) RDS(ON) (mΩ Ω) N-Channel RDS(ON) vs. Input Voltage 600 550 85°C 500 450 25°C 400 120°C 550 500 85°C 450 400 25°C 350 350 300 300 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 6.0 3.0 Input Voltage (V) (300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7µ µF) IO 300mA 1mA IL 0 1.90 1.85 Output Voltage (top) (V) VO VO 1.80 1.75 IO 400mA 300mA 0.4 0.3 IL 0.2 0.1 Time (50µs/div) 6.0 Time (50µs/div) Load Transient Response Load Transient Response (300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10µ µF) (300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10µ µF; C4 = 100pF) 400mA 300mA 0.4 0.3 IL 0.2 0.1 Time (50µs/div) APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 1.825 Output Voltage (top) (V) 1.80 1.850 VO 1.800 1.775 IO 400mA 300mA 0.4 0.3 IL 0.2 0.1 Load and Inductor Current (200mA/div) (bottom) VO Load and Inductor Current (200mA/div) (bottom) 1.90 IO 5.5 Load and Inductor Current (200mA/div) (bottom) Output Voltage (top) (V) 5.0 Load Transient Response 1.7 1.75 4.5 Load Transient Response 1.8 1.85 4.0 Input Voltage (V) Load and Inductor Current (200mA/div) (bottom) 1.9 3.5 (1mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10µ µF; CFF = 100pF) 2.0 Output Voltage (top) (V) 100°C 600 Time (50µs/div) 7 APS1056 Fast Transient 600mA Step-Down Converter Typical Characteristics Output Ripple (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA) 6.0 1.82 Output Voltage (top) (V) 5.0 1.79 4.5 1.78 4.0 1.77 3.5 1.76 3.0 Input Voltage (bottom) (V) 1.80 Time (25µ µs/div) 40 20 0.30 0.25 VO 0 0.20 -20 0.15 -40 0.10 -60 0.05 IL -80 0.00 -100 -0.05 -120 Inductor Current (bottom) (A) 5.5 1.81 Output Voltage (AC coupled) (top) (mV) Line Response (VOUT = 1.8V @ 400mA) -0.10 Time (10µs/div) Output Ripple 0.9 40 20 0.8 VO 0 0.7 -20 0.6 -40 0.5 -60 0.4 0.3 -80 -100 IL Inductor Current (bottom) (A) Output Voltage (AC coupled) (top) (mV) (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) 0.2 0.1 -120 Time (500ns/div) 8 (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Functional Block Diagram VIN OUT See note Err Amp . DH Voltage Reference LX Logic DL EN INPUT GND Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly to the internal error amplifier. Functional Description The APS1056 is a high performance 600mA 1.4MHz monolithic step-down converter. It has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 4.7µH inductor and a 4.7µF ceramic capacitor are recommended (see table of values). The fixed output version requires only three external power components (CIN, COUT, and L). The adjustable version can be programmed with external feedback to any voltage, ranging from 0.6V to the APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) input voltage. An additional feed-forward capacitor can also be added to the external feedback to provide improved transient response (see Figure 1). At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the RDSON drop of the P-channel highside MOSFET. The input voltage range is 2.7V to 5.5V. The converter efficiency has been optimized for all load conditions, ranging from no load to 600mA. The internal error amplifier and compensation provides excellent transient response, load, and line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. 9 APS1056 Fast Transient 600mA Step-Down Converter 1 2 3 Enable VIN VOUT =1.8V C4 100pF U1 APS1056 EN R1 OUT L1 118k 4.7µH GND VIN LX C1 10µF C3 n/a R2 59k C2 4.7µF GND LX GND2 U1 APS1056 SOT23-5 L1 CDRH3D16-4R7 C2 4.7µF 10V 0805 X5R C1 10µF 6.3V 0805 X5R Figure 1: Enhanced Transient Response Schematic. Control Loop The APS1056 is a peak current mode step-down converter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as short circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor. The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. For fixed voltage versions, the error amplifier reference voltage is internally set to program the converter output voltage. For the adjustable output, the error amplifier reference is fixed at 0.6V. Soft Start / Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the APS1056 10 into a low-power, non-switching state. The total input current during shutdown is less than 1µA. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited. To minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. Switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Applications Information Inductor Selection The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the adjustable and low-voltage fixed versions of the APS1056 is 0.24A/µsec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7µH inductor. 0.75 ⋅ VO 0.75 ⋅ 1.5V A m= = = 0.24 L 4.7µH µsec This is the internal slope compensation for the adjustable (0.6V) version or low-voltage fixed versions. When externally programming the 0.6V version to 2.5V, the calculated inductance is 7.5µH. 0.75 ⋅ VO L= = m =3 show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. The 4.7µH CDRH3D16 series inductor selected from Sumida has a 105mΩ DCR and a 900mA DC current rating. At full load, the inductor DC loss is 17mW which gives a 2.8% loss in efficiency for a 600mA, 1.5V output. Input Capacitor Select a 4.7µF to 10µF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = µsec 0.75 ⋅ VO ≈ 3 A ⋅ VO A 0.24A µsec In this case, a standard 6.8µH value is selected. For high-voltage fixed versions (≥2.5V), m = 0.48A/ µsec. Table 1 displays inductor values for the APS1056 fixed and adjustable options. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. The inductor should not 0.6V Adjustable With External Feedback Fixed Output ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 µsec ⋅ 2.5V = 7.5µH A Configuration V ⎞ VO ⎛ · 1- O VIN ⎝ VIN ⎠ CIN(MIN) = 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10µF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6µF. Output Voltage Inductor 1V, 1.2V 2.2µH 1.5V, 1.8V 4.7µH 2.5V, 3.3V 6.8µH 0.6V to 3.3V 4.7µH Table 1: Inductor Values. APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 11 APS1056 Fast Transient 600mA Step-Down Converter The maximum input capacitor RMS current is: IRMS = IO · VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current. VO ⎛ V ⎞ · 1- O = VIN ⎝ VIN ⎠ D · (1 - D) = 0.52 = 1 2 VO IO 2 ⎛ V ⎞ · 1- O The term VIN ⎝ VIN ⎠ appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the APS1056. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C2) can be seen in the evaluation board layout in Figure 2. A laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result. 12 In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. Output Capacitor for VIN = 2 · VO IRMS(MAX) = Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7µF to 10µF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output voltage droop during the three switching cycles to the output capacitance can be estimated by: COUT = 3 · ∆ILOAD VDROOP · FS Once the average inductor current increases to the DC load level, the output voltage recovers. The above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation also limits the minimum output capacitor value to 4.7µF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater phase margin. (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Figure 2: APS1056 Sample Layout Top Side. Figure 3: Exploded View of Sample Layout Figure 4: APS1056 Sample Layout Bottom Side. The maximum output capacitor RMS ripple current is given by: IRMS(MAX) = 1 VOUT · (VIN(MAX) - VOUT) L · F · VIN(MAX) 2· 3 · Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. Adjustable Output Resistor Selection For applications requiring an adjustable output voltage, the 0.6V version can be externally programmed. Resistors R1 and R2 of Figure 5 program APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R2 is 59kΩ. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 2 summarizes the resistor values for various output voltages with R2 set to either 59kΩ for good noise immunity or 221kΩ for reduced no load input current. ⎛ VOUT ⎞ ⎛ 1.5V ⎞ R1 = V -1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ ⎝ REF ⎠ ⎝ ⎠ 13 APS1056 Fast Transient 600mA Step-Down Converter The adjustable version of the APS1056, combined with an external feedforward capacitor (C4 in Figure 1), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor C1 for stability. R2 = 59kΩ R2 = 221kΩ VOUT (V) R1 (kΩ) R1 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75K 113K 150K 187K 221K 261K 301K 332K 442K 464K 523K 715K 1.00M Thermal Calculations There are three types of losses associated with the APS1056 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the LDO losses is given by: PTOTAL = IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO]) VIN + (tsw · F · IO + IQ) · VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load stepdown converter switching losses. Table 2: Adjustable Resistor Values For Use With 0.6V Step-Down Converter. 1 2 3 Enable VIN U1 APS1056 EN R1 OUT GND 118k VOUT VIN L1 LX C1 10µF 4.7µH C2 4.7µF R2 59k GND GND2 LX U1 APS1056 SOT23-5 L1 CDRH3D16-4R7 C1 10µF 10V 0805 X5R C2 4.7µF 10V 0805 X5R Figure 5: APS1056 Adjustable Evaluation Board Schematic. 14 (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = IO2 · RDSON(HS) + IQ · VIN Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. Given the total losses, the maximum junction temperature can be derived from the θJA for the SOT23-5 package which is 160°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB Layout The suggested PCB layout for the APS1056 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 1. The input capacitor (C2) should connect as closely as possible to VIN (Pin 3) and PGND (Pins 6-8). 2. C1 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. 3. The feedback trace or OUT pin (Pin 2) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. If external feedback resistors are used, they should be placed as closely as possible to the OUT pin (Pin 2) to minimize the length of the high impedance feedback trace. 4. The resistance of the trace from the load return to the PGND (Pins 6-8) should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. A high density, small footprint layout can be achieved using an inexpensive, miniature, nonshielded, high DCR inductor. APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 15 APS1056 Fast Transient 600mA Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 600mA (adjustable using 0.6V version), Pulsed Load ∆ILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 1.4MHz TAMB = 85°C 1.8V Output Inductor L1 = 3 µsec µsec ⋅ VO2 = 3 ⋅ 1.8V = 5.4µH A A (use 4.7µH; see Table 1) For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ. ∆IL1 = ⎛ VO V ⎞ 1.8V 1.8V ⎞ ⎛ ⋅ 1- O = ⋅ ⎝1 = 156mA L1 ⋅ F ⎝ VIN ⎠ 4.7µH ⋅ 1.4MHz 4.2V ⎠ IPKL1 = IO + ∆IL1 = 0.6A + 0.068A = 0.668A 2 PL1 = IO2 ⋅ DCR = 0.6A2 ⋅ 105mΩ = 38mW 1.8V Output Capacitor VDROOP = 0.1V COUT = IRMS = 3 · ∆ILOAD 3 · 0.3A = = 6.4µF; use 10µF VDROOP · FS 0.1V · 1.4MHz 1 2· 3 · (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 45mArms = L1 · F · VIN(MAX) 2 · 3 4.7µH · 1.4MHz · 4.2V Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10µW 16 (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Input Capacitor Input Ripple VPP = 25mV CIN = IRMS = ⎛ VPP ⎝ IO 1 1 = = 4.87µF; use 4.7µF ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 1.4MHz - ESR · 4 · FS ⎠ ⎝ 0.6A ⎠ IO = 0.3Arms 2 P = esr · IRMS2 = 5mΩ · (0.3A)2 = 0.45mW APS1056 Losses PTOTAL = IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO]) VIN + (tsw · F · IO + IQ) · VIN = 0.62 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V]) 4.2V + (5ns · 1.4MHz · 0.6A + 70µA) · 4.2V = 118mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 118mW = 103.9°C APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 17 APS1056 Fast Transient 600mA Step-Down Converter Adjustable Version (0.6V device) R2 = 59kΩ R2 = 221kΩ1 VOUT (V) R1 (kΩ) R1 (kΩ) L1 (µH) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75.0 113 150 187 221 261 301 332 442 464 523 715 1000 2.2 2.2 2.2 2.2 2.2 2.2 4.7 4.7 4.7 4.7 6.8 6.8 6.8 Fixed Version R2, R4 Not Used VOUT (V) R1 (kΩ) L1 (µH) 0.6-3.3V 0 4.7 Table 3: Evaluation Board Component Values. Manufacturer Sumida Sumida Sumida MuRata MuRata Coilcraft Coiltronics Coiltronics Coiltronics Part Number Inductance (µH) Max DC Current (A) DCR (Ω) Size (mm) LxWxH Type CDRH3D16-2R2 CDRH3D16-4R7 CDRH3D16-6R8 LQH2MCN4R7M02 LQH32CN4R7M23 LPO3310-472 SD3118-4R7 SD3118-6R8 SDRC10-4R7 2.2 4.7 6.8 4.7 4.7 4.7 4.7 6.8 4.7 1.20 0.90 0.73 0.40 0.45 0.80 0.98 0.82 1.30 0.072 0.105 0.170 0.80 0.20 0.27 0.122 0.175 0.122 3.8x3.8x1.8 3.8x3.8x1.8 3.8x3.8x1.8 2.0x1.6x0.95 2.5x3.2x2.0 3.2x3.2x1.0 3.1x3.1x1.85 3.1x3.1x1.85 5.7x4.4x1.0 Shielded Shielded Shielded Non-Shielded Non-Shielded 1mm Shielded Shielded 1mm Shielded Table 4: Typical Surface Mount Inductors. 1. For reduced quiescent current, R2 and R4 = 221kΩ. 18 (PRELIMINARY INFORMATION) APS1056.2007.04.0.9 APS1056 Fast Transient 600mA Step-Down Converter Manufacturer MuRata MuRata MuRata Part Number Value Voltage Temp. Co. Case GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39 4.7µF 10µF 22µF 10V 6.3V 6.3V X5R X5R X5R 0805 0805 0805 Table 5: Surface Mount Capacitors. APS1056.2007.04.0.9 (PRELIMINARY INFORMATION) 19 APS1056 Fast Transient 600mA Step-Down Converter Ordering Information Output Voltage1 Package 1.8 Adj ≥ 0.6 SOT23-5 SOT23-5 Marking2 Part Number (Tape and Reel)3 APS1056IGV-1.8-T1 APS1056IGV-0.6-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/pbfree. Package Information SOT23-5 2.85 ± 0.15 1.90 BSC 0.40 ± 0.10 0.075 ± 0.075 0.15 ± 0.07 4° ± 4° 10° ± 5° 1.10 ± 0.20 0.60 REF 1.20 ± 0.25 2.80 ± 0.20 1.575 ± 0.125 0.95 BSC 0.60 REF 0.45 ± 0.15 GAUGE PLANE 0.10 BSC All dimensions in millimeters. 1. 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