AMS4123 AMS | Alldatasheet
Document overview
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- PDF pages: 18
Technical content
Features
- Step-Down Converter + LDO in SO-8EP
- Internally Compensated
- Up to 95% Efficiency
- Low ESR Ceramic Output Capacitor Stable
- Soft Start
- Under-Voltage Lockout
- Dual Threshold Enable
- 300 kHz Switching Frequency
- Hiccup Current Limit
- Over-Temperature Shutdown
- Ultra-Low Dropout LDO 350mV @ 1A
- Up to 3A Step-Down Output Current
- Up to 1A LDO Output Current
- Excellent Light Load Efficiency
Applications
- Audio Power Amplifiers
- Portable (Notebook) Computers
- Point of Regulation for High Performance Electronics
- Consumer Electronics
- DVD, Blue-ray DVD writers
- LCD TVs and LCD monitors
- Distributed Power Systems
- Battery Chargers
- Pre-Regulator for Linear Regulation Typical Application 10uH 220nF 10.0k 31.6k 10.0k B340LB 20.0k 2.2uF 10uF 4.7nF 22uF 100uF R1 and R4 Voltage Options 3.3V 45.3k 2.5V 31.6k 5.0V 73.2k 1.8V 20.0k 2.5V at 2A 1.8V at 1A Enable Vin 4.5V to 20V LDOout8 EN 4 Vin3 BST 2 SW 1 FB LDO6 LDOin7 FB SW 5 U1 AMS4123 2.5V SW out
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Pin # Symbol Description
1 SW Step-Down converter switching node that connects the internal power switch to the
output inductor.
2 BST
The bootstrap capacitor tied to this pin is used as the bias source for the drive to the internal power switch. Use a 220nF or greater capacitor from the BST to the SW pin.
3 Vin
Input Power. Supplies bias to the IC and is also the power input to the step-down converter main power switch. Bypass Vin with low impedance ceramic with sufficient capacitance to minimize switching frequency ripple as well as high frequency noise. 4 EN Enable. A voltage greater than 2V at this pin enables the switching regulator. 2.5V enables the LDO section.
5 FB SW
Step-Down Converter Feedback input. A resistor network of two resistors is used to set-up the output voltage connected between VSW out and GND. The node between the two resistors is connected to Feedback Switch pin.
6 FB LDO
LDO Feedback input. A resistive voltage divider is used to set the output voltage connected between the LDO output and GND. The node between the two resistors is connected to FB LDO pin. 7 LDO in LDO Input. Connect to the output of the Step-Down converter. LDO IN can also be powered from any power supply as long as it is 2V less than Vin. 8 LDO out LDO Output pin. 9 GND (PADDLE) Ground paddle to be connected to PCB ground plane. This is also the ground for internal voltage reference. Pin Configuration 8L SOIC Top View
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Absolute Maximum Ratings (1) Storage Temperature Range……………...-65 ⁰C to 150⁰C Recommended Operating Conditions (2) Ambient Operating Temperature…… …………….-40 ⁰C to 85⁰C Thermal Information 8L SOIC EP θJA (3) Electrical Characteristics TA= 25 °C and VIN=12V (unless otherwise noted). Parameter Symbol Conditions Min. Typ. Max. Units Vin V in 4.5 12 20 V LDO Feedback Voltage V FBLDO I LDO=0A tbd 0.586 tbd V Switcher Feedback Voltage V FBSW I sw=0A tbd 0.596 tbd V LDO Output Voltage tolerance V LDO Out VLDO out=0.6V to 5V in 100mV increments -1.5 1 1.5 % Step-Down Converter Bias Current IQSW VLDOin =VEN =5V VFBSW= 1.5V 1.4 1.9 mA LDO+SW Bias Current I QSW+LDO VLDOin =VEN =5V VFBLDO =VFBSW= 1.5V 1.3 2.0 mA LDO Bias Current I QLDO V EN= 5V; VFBLDO = 1.5V 400 μA Shutdown Supply Current I Vinsd V EN =0V 90 nA SW NPN Saturation Voltage V SAT I SW out=1A 0.66 V Converter Current Limit ILIMSW V SW out=5V 4.2 A LDO Current Limit I LIMLDO VLDO in=5V; Co=2.2μF 1.1 A LDO Dropout Voltage V DO V LDOin=VLDOout-0.1V, Io=1A 350 mV LDO Load Regulation ΔVLDO Out / VLDO Out ILDO = 0 to1A 0.5 % LDO Line Regulation ΔVLDO Out / VLDO Out VLDOin = VLDOout+0.5V to 20V, Vin=20V 0.1 % Oscillator Frequency F OSC 260 300 340 kHz Maximum Duty Cycle D MAX V FB=0V 95 99 % Minimum Duty Cycle D MIN V FB=1.5V 0 % Converter Enable Threshold V EN SW 2.0 2.1 V Enable Hysteresis V ENHYS 100 mV LDO Enable Threshold V EN LDO 2.5 2.55 V Enable Pull-up Current I EN V EN = 0V 0.7 μA Under Voltage Lockout V UVLO V in rising 4.2 V Under Voltage Lockout Hysteresis VUVLO HYS 200 mV Total Power dissipation P D Note (4) 2.5 W Thermal Shutdown T SD 145 °C
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Notes: 1. Stresses above those listed in Absolute Maximu m Ratings may cause permanent damage to the device. 2. Operation outside of the recommended operating conditions is not guaranteed. 3. Measured on approximately 1” square of 1 oz. copper. 4. The total power dissipation for SO-8 ED P package is recommended to 2.5W rated at 25⁰C ambient temperature. The thermal resistance Junction to Case is 45⁰C/W. Total power dissipation for the switching regulator and the LDO should be taken in consideration when calculating the output current capability of each regulator.
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0.01 0.1 1 10 Efficiency (%) Output Current (A) Efficiency VSW out=5V, L=10µH, B340LB Schottky Vin =12V Vin =23V 100 0.01 0.1 1 10 Efficiency (%) Output Current (A) Efficiency VSW out=3.3V, L=10µH, B340LB Schottky Vin =12V Vin =23V 100 0.01 0.1 1 10 Efficiency (%) Output Current (A) Efficiency Vsw out=2.5V, L=10µH, B340LB Schottky Vin =12V Vin =23V -1.0 -0.6 -0.2 0.2 0.6 1.0 0.01 0.1 1 10 VSW out Regulation (%) Output Current (A) Load Regulation V SW out =5V, L=10µH Vin =12V Vin =23V -1.0 -0.6 -0.2 0.2 0.6 1.0 0.01 0.1 1 10 VSW out Regulation (%) Output Current (A) Load Regulation V SW out=3.3V, L=10µH Vin =12V Vin =23V -1.0 -0.6 -0.2 0.2 0.6 1.0 0.01 0.1 1 10 VSW out Regulation (%) Output Current (A) Load Regulation V sw out=2.5V, L=10 µH Vin =12V Vin =23V
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0.0 0.8 1.6 2.4 3.2 0 5 10 15 20 25 Input Current (mA) Input Voltage (V) No Load Input Current vs. Input Voltage Vsw out = 2.5V, VLDO out = 1.8V 292 296 300 304 308 0 5 10 15 20 25 Switching Frequency (kHz) Input Voltage (V) Switching Frequency vs. Input Voltage Vsw out = 2.5V, VLDO out = 1.8V 0.5 1.5 0 0.2 0.4 0.6 0.8 1 VLDO Out Voltage (V) Output Current (A) VLDO Out Load Regulation VSW out = VLDO in =2.5V, VLDO Out=1.8V Vin=20V Vin=15V Vin=12V -0.50 -0.25 0.00 0.25 0.50 0 5 10 15 20 25 Output Error (%) Input Voltage Vin (V) Output Voltage Error vs. Input Voltage VSW out = VLDO in = 2.5V, VLDO out =1.8V V LDO out Vsw out ILDO=0.6A Isw=1.6A 0.1 0.2 0.3 0.4 0 0.2 0.4 0.6 0.8 1 Dropout Voltage (V) LDO Output Current (V) LDO Dropout Voltage vs. Load Current VLDO in = VLDO out -0 . 1 V VLDO out programmed for 1.8V Vin = 12V 0.57 0.58 0.59 0.60 0.61 -50 -10 30 70 110 150 Feedback Voltage (V) Ambient Temperature (ºC) Feedback Voltage Temperature Variation FBLDO FBSW ILDO=Isw=0 VLDO out=1.8V, VSW out=2.5V
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20 µsec/div Step-Down Converter Load Transient 200mA to 1.2A, Vsw out = 2.5V,Vin=12V ISW out 500mA /div VSW out 100mVac /div 40 µsec/div Step-Down Converter Load Transient 200mA to 2A, Vsw out = 2.5V, Vin=12V ISW out 500mA /div VSW out 100mVac /div 2 µsec/div LDO 200mA to 800mA Transient Response, VLDO in=3.3V, Co=2.2µF, VLDO out = 1.8V, Vin=12V ILDO out 500mA /div VLDO out 100mVac /div 20 µsec/div LDO Transient Response No Load to 1A, VLDO in=Vsw out =2.5V, ILDO out 1A/div VLDO out 100mVac /div VSW out 200mVac/ div ISW out 1A/div VSW out 100mVac /div 2 msec/div Step-Down Converter Load Transient No Load to 2A,VSW out=2.5V, Vin=12V 1 µsec/div VSW out 20mVac /div IL 1A/div VSW 5V/div Step-Down Converter Output Ripple VSW out =2.5V, ISW out=1.8A, Vin=12V
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-45 -10 25 60 95 130 Switching Frequency (kHz) Ambient Temperature (ºC) Switching Frequency Temperature Variation VSW out=2.5V, Vin=12V -2.4 -1.6 -0.8 0.0 0.8 -50 -10 30 70 110 150 Feedback Voltage Error (%) Ambient Temperature (ºC) Feedback Voltage Temperature Variation FBLDO FBSW ILDO=Isw=0 VLDO out=1.8V, VSW out=2.5V 0.3 0.6 0.9 1.2 Vcesat (V) Current (A) Step-Down Converter Power Switch Saturation Voltage V in=12V Tamb = 25⁰ C Mounted on Eval. Board 1 msec/div Start-Up Response Vin=20V VSW out 1V /div VLDO out 1V /div Ven 5V /div IL 2A/div 2 msec/div Start-Up Response Enable=Vin=12V VLDO out 1V /div Vin 10V /div IL 2A/div 400 µsec/div Start-Up Response Vin=12V VSW out 1V /div VLDO out 1V /div Ven 5V /div IL 2A/div
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0.6 0.7 0.8 0.9 1.1 1.2 1.3 1.4 5 9 13 17 21 25 Current Limit (A) Vin Input Voltage (V) LDO Current Limit VLDO in = 3.3V, VLDO out =1.8V Voltage Mode Load VLDO out = 1.68V 0 200 400 600 800 1000 Ground Current (mA) Load Current (mA) LDO Ground Current VLDO in = 3.3V, VLDO out=1.8V
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P UVLO 2.0V 2.5V 4.2V / 3.8V Internal Vcc Regulator 300kHz Oscillator Vcc 3.3V PVin Σ Isense Q Q SET CLRS R EAout EAout 0.6V Vref 0.6V Switching Regulator Shutdown BST Reg. SW out
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The AMS4123 is combines a high voltage 3 Amp fixed frequency step-down converter combined with a 1 Amp low drop out (LDO) linear regulator on a single die. The peak current mode step-down converter has internal compensation and is stable with a wide range of ceramic, tantalum, and electrolytic output capacitors. The step-down converter output voltage is sensed through an external resistive divider that feeds the negative input to an internal transconductance error amplifier. The output of the error amplifier is connected to the input to a peak current mode comparator. The inductor current is sensed as it passes through the power switch, amplified and is also fed to the current mode comparator. The error amplifier regulates the output voltage by controlling the peak inductor current passing through the power switch so that, in steady state, the average inductor current equals the load current. The step-down converter has an input voltage range of 4.5V to 20V with an output voltage as low as 0.6V. The LDO operates from an input voltage ranging from 1V to 20V and a typical dropout voltage of 350mV at 1A. The input to the LDO can be supplied by the output of the Step-Down converter or some other available power source that must be 2V less than the input voltage (Vin). The LDO is also stable for a wide range of ceramic output capacitors ranging from as low as 1µF. Enable The enable input has two levels so that the step-down converter can be enabled independently of the LDO. The enable threshold for the step-down converter is 2.0V while the enable threshold for the linear regulator output is 2.5V typical. Under Voltage Lockout The under-voltage lockout (UVLO) feature guarantees sufficient input voltage (Vin) bias for proper operation of all internal circuitry prior to activation. The input voltage (Vin) is internally monitored and the converter and LDO are enabled when the rising level of Vin reaches 4.2V. To prevent UVLO chatter 400mV of hysteresis is built in to the UVLO comparator so that the step-down converter and LDO are disabled when VIN drops to 3.8V. Fault Protection Short circuit and over-tem perature shutdown disable the converter and LDO in the event of an overload condition. Application Inductor The step-down converter inductor is typically selected to limit the ripple current to 40% of the full load output current. Solve for this value at the maximum input voltage where the inductor ripple current is greatest. L=ሺVin-Voሻ· Vo Vin·Io·0.4·Fs L=ሺ15V-2.5Vሻ· 2.5V 15V·2A·0.4·300kHz =9.4µH For most applications the duty cycle of the AMS4123 step down converter is less than 50% duty and does not require slope compensation for stability. This provides some flexibility in the selected inductor value. Given the above sele cted value, others values slightly greater or less may be examined to determine the effect on efficiency without a detrimental effect on stability. With and inductor value selected, the ripple current can be calculated: Ipp= (Vo+Vfwd)·(1-D) L·Fs Using the maximum input voltage values the ripple is: Ipp= (2.5V+0.2V)·ሺ1-0.23 ሻ 10μH·300kHz =0.7A Once the appropriate value is determined, the component is selected bas ed on the DC current and the peak (saturation) current. Select an inductor that has a DC current rating greater than the full load current of the application. The DC current rating is also reflected in the DC resistance (DCR) specification of the inductor. The inductor DCR should limit the inductor loss to less than 2% of the step- down converter output power. The peak current at full load is equal to the full load DC current plus one half of the ripple current. As mentioned before, the ripple current varies with input
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non-shielded inductors available. Table 1 lists a few. Table 1. Inductor Selection Guide capacitor to minimize the switching frequency ripple. examined for the load application and load removal.
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rated to withstand the input voltage. duty cycle approaches 50% where it is a maximum. requirements during the load transient. bypass capacitor at the LDO input. Table 2. Feedback Resistor values
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- Vin Capacitor. A low ESR ceramic bypass
- Schottky Diode. During the off portion of the
- Feedback Resistors. The feedback resistors
should be placed as close as possible the IC.
- Inductor. Minimize the length of the SW node
- Ground. The most quiet ground or return potential
- For good thermal performance vias are required
be 0.3mm to 0.33mm positioned on a 1.2mm grid. Figure 1. Step Down Converter Layout
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Output Power and Thermal Limits The AMS4123 junction temperature, Step-Down converter and LDO current capability depends on the internal dissipation and the junction to case thermal resistance of the SO8 exposed paddle package. This gives the junction temperature rise above the device paddle and PCB temperature. The temperature of the paddle and PCB will be elevated above the ambient temperature due to the total losses of the step down converter and losses of other circuits and or converters mounted to the PCB. Tjmax=Pd·θjc+Tpcb+Tamb The losses associated with the AMS4123 overall efficiency are; 1. Output Diode Conduction Losses 2. Inductor DCR Losses 3. AMS4123 Internal losses a. Power Switch Forward Conduction and Switching Losses b. Quiescent Current Losses The internal losses contribute to the junction temperature rise above the case and PCB temperature. The junction temperature depends on many factors and should always be verified in the final application at the maximum ambient temperature. This will assure that the device does not enter over-temperature shutdown when fully loaded at the maximum ambient temperature.
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Figure 2. AMS4123 Evaluation Board Top Side Figure 3. AMS4123 Evaluation Board Bottom Side Figure 4. AMS4123 Evaluation Board Schematic Table 3. Evaluation Board Bill of Materials
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R2,R3 10k Ω, 0.1W, 0603 1% Various CRCW060310K0FKEA R1,R4 See table 2 Various CRCW0603xxKxFKEA D1 3A, 40V Schottky Diodes Inc. B340LB U1 Step-Down Converter / LDO AMS AMS4123
ORDERING INFORMATION
PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted.
8 LEAD SOIC PLASTIC PACKAGE (S)
TEMP. RANGE AMS4123S -25°C to 125°C
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