Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters General Description Features The AP3421/A/B is a fully integrated dual output voltage regulator. The two converters are current mode and internally compensated. The converters include integrated control and synchronous rectifier switches. The outputs are both rated for up to 1A. Both outputs are adjustable using external resistors. • • • • • • • • • • • • • • • • The step-down converters operate at 1.3MHz fixed switching frequency under normal load and in a pulse skipping mode for light loads. The switching clock is shifted 180° for SW2. The E/S pin provides an enable function and allows the converter to be synchronized to an external clock. With E/S held low, the AP3421/A/B draws less than 10μA current. In the start-up sequence, the VO1 output is designed to precede the VO2 output. The two outputs have controlled start-up sequence. AP3421/A/B VO1=1.8 to 3.6V at 1A VO2=1.0 to 3.6V at 1A Switching Frequency: 1.3MHz 180° Phase Shifted Switching No Rectifier Diode Required Optional External Clocking (2× Clock Required) Light Load Pulse Skipping Enable/Sleep State Internal Soft-start Open-drain Power On Reset Monitors Input and Outputs Discharge-Before-Turn-On (For AP3421/A) Pre-bias Function (For AP3421B) Peak Over Current Protection Short Circuit Protection Over Temperature Shutdown Applications • • Power On Reset (POR) function is provided by means of an open-drain output present on the POR pin. The POR function monitors VMON, FB1 and FB2, and pulls low if any of these begin to drop out. The POR is internally deglitched and provides a delayed recovery/reset time. Hard Disk Drivers Set Top Boxes The AP3421/A/B provides peak over-current protection, short circuit protection and thermal shutdown. Discharge-Before-Turn-On discharges the outputs completely before soft-starting to always bring them up in the proper sequence at start-up or after a POR (For AP3421/A only). The AP3421/A/B is available in DFN-3×3-10 package. DFN-3×3-10 Figure 1. Package Type of AP3421/A/B May. 2011 Rev. 1.3 BCD Semiconductor Manufacturing Limited 1 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Pin Configuration DN Package (DFN-3×3-10) P in 1 D ot by M arking Figure 2. Pin Configuration of AP3421/A/B (Top View) Pin Description Pin Number May. 2011 Pin Name 1 FB2 2 AVIN 3 PVIN 4 SW2 5 PGND 6 SW1 7 E/S Function Feedback from VO2. Connect voltage divider to the load side of VO2 output inductor-capacitor filter Analog power input. Connect a 1μF ceramic capacitor between this pin and AGND Control MOSFET switch power input. Connect a 10μF ceramic capacitor between this pin and PGND, as close to the IC as possible VO2 synchronous buck switching output. Connect to VO2 inductor Power ground connection. Synchronous rectifier MOSFET source. Provide a star connection between this pin, VO1, VO2 filter capacitor returns, VIN input capacitor return, and AGND. Keep the star connection as close to the IC as possible VO1 synchronous buck switching output. Connect to VO1 inductor Enable/Synchronization. Pulling this pin high statically enables the IC and pulling the pin low statically will shut down the IC. Applying a pulse to this pin will synchronize SW1 and SW2 switching frequency to ½ the external clock frequency Rev. 1.3 BCD Semiconductor Manufacturing Limited 2 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Pin Description (Continued) Pin Number May. 2011 Pin Name 8 POR 9 VMON 10 FB1 11 AGND Function Power on reset output pin. Monitors FB1, FB2 output voltage levels and VIN. POR is pulled low if an output voltage drop is detected on FB1 or FB2 or VIN, and is Hi-Z during normal operation Voltage monitor–supervisor for one external voltage (could be input voltage). The POR output is triggered if this output falls below the VMON threshold Feedback from VO1. Connect voltage divider to the load side of VO1 output inductor-capacitor filter Signal ground connection. Provide a star connection between this pin and PGND pin Rev. 1.3 BCD Semiconductor Manufacturing Limited 3 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Functional Block Diagram Figure 3. Functional Block Diagram of AP3421/A/B May. 2011 Rev. 1.3 BCD Semiconductor Manufacturing Limited 4 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Ordering Information AP3421 - Circuit Type G1: Green A: AP3421A B: AP3421B Blank: AP3421 TR: Tape & Reel Package DN: DFN-3×3-10 Package Temperature Range DFN-3×3-10 -40 to 85°C Part Number Marking ID AP3421DNTR-G1 BCB AP3421ADNTR-G1 BDD AP3421BDNTR-G1 BDE Packing Type Tape & Reel BCD Semiconductor's Pb-free products, as designated with "G1" suffix in the part number, are RoHS compliant and green. Absolute Maximum Ratings (Note 1) Parameter Input Voltage Feedback Voltage E/S Pin Voltage SW1, SW2 Pin Voltage Thermal Resistance Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10sec) Symbol Value Unit VIN VFB VE/S VSW θJA TJ TSTG TLEAD -0.3 to 7 -0.3 to VIN+0.3 -0.3 to VIN+0.3 VPGND-1 to VIN+1 33 150 -25 to 150 260 V V V V ºC /W ºC ºC ºC Note 1: Stresses greater than those listed under “Absolute 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 under “Recommended Operating Conditions” is not implied. Exposure to “Absolute Maximum Ratings” for extended periods may affect device reliability. Recommended Operating Conditions Parameter Input Voltage VO1 Maximum Output Current VO2 Maximum Output Current Operating Ambient Temperature May. 2011 Symbol VIN AP3421 AP3421A/B IO1 (Max) IO2 (Max) TA Rev. 1.3 Min Max Unit 4.5 3.0 1 1 -40 5.5 5.5 V 85 A A °C BCD Semiconductor Manufacturing Limited 5 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Electrical Characteristics VIN =VE/S=5V, TA=25℃, unless otherwise specified. Parameter Symbol Operating Input Voltage Supply Current Shutdown Supply Current Under Voltage Lockout Threshold Under Voltage Lockout Hysteresis POR Threshold VMON Feedback Voltage Switch Current Limit Oscillator Frequency Soft-start Time POR Threshold FB1 POR Threshold FB2 Discharge Complete Threshold (AP3421/A ) VIN Conditions AP3421 AP3421A/B ICC ISHDN AP3421 AP3421A/B VHUVLO VVMON_POR VFB1, VFB2 ILIM1 ILIM2 fOSC1, fOSC2 tSS_FB1 VFB1_POR VFB2_POR 4.5 3.0 VVMON Falling FB11Falling1 FB21Falling1 FB1 Level Where Discharge Cycle Is Terminated fSWITCHING=50%×fE/S When Externally Clocked fE/S_MAX POR Release Delay Time tPOR_HOLD POR Low Voltage VPOR_LOW VO2 Start Threshold (AP3421/A ) VFB1_ST SW1, SW2 Discharge Resistance RSTOP_SW1,2 AP3421, AP3421A/B on AP3421A/B Thermal Shutdown Threshold Thermal Shutdown Hysteresis May. 2011 0.97 0.975 1.2 1.2 1.0 0.5 86 86 3.5 2.7 300 1.00 1.0 1.6 1.6 1.30 1.0 89 89 50 75 5.5 5.5 1.0 10 4.0 3.0 1.03 1.025 Unit V mA μA V mV V V A 1.60 2.0 92 92 MHz ms %VFB1 %VFB2 100 mV V 1.5 fE/S_MIN tPOR_DELAY 5.0 3.3 0.6 Frequency Lock-in Range Internal MOSFET Resistance 3.0 2.4 Rising Edge VFB1_DCT POR Assert Delay Time Typ Max VFB1=VFB2=1.2V VE/S=0V, VIN=5.0V VEN_L VEN_H E/S Pin Threshold Min Fault Flag Set to POR Pull Low Fault Flag Reset to POR Hi-Z State POR Sinking 4mA FB1 Rising Voltage for FB2 to Initiate Soft-start Discharge1Resistance for SW1, SW2 VIN=5.0V ISW=100mA VIN=5.0V ISW=-100mA VIN=3.3V ISW=100mA VIN=3.3V ISW=-100mA RDS_SW1_U RDS_SW2_U RDS_SW1_L RDS_SW2_L RDS_SW1_U RDS_SW2_U RDS_SW1_L RDS_SW2_L TOTSD THYS Rev. 1.3 1.5 MHz 3.0 10 25 40 μs 10 20 30 ms 300 mV 86 89 92 %VFB1 15 30 45 Ω 10 277 260 249 160 300 280 260 180 160 20 mΩ 30 ºC ºC BCD Semiconductor Manufacturing Limited 6 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Typical Performance Characteristics VIN=VE/S=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3μH, C1=C3=10μF, C2=C2’=10μF, TA=25°C, unless otherwise specified. 0.66 1200 0.64 1000 Supply Current (mA) SW1, SW2 Frequency (kHz) 0.62 800 600 400 0.60 0.58 0.56 0.54 0.52 200 0.50 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 VFB1=VFB2=1.2V 0.48 -60 5.8 -40 -20 0 40 60 80 100 120 140 Temperature ( C) Figure 4. SW1, SW2 Frequency vs. Input Voltage Figure 5. Supply Current vs. Temperature 2.0 2.0 1.8 1.8 1.6 1.6 Current Limit 2 (A) Current Limit 1 (A) 20 o Input Voltage (V) 1.4 1.2 1.0 0.8 1.4 1.2 1.0 0.8 0.6 -60 -40 -20 0 20 40 60 80 100 120 0.6 -60 140 O -20 0 20 40 60 80 100 120 140 Temperature ( C) Figure 7. Current Limit 2 vs. Temperature Figure 6. Current Limit 1 vs. Temperature May. 2011 -40 O Temperature ( C) Rev. 1.3 BCD Semiconductor Manufacturing Limited 7 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Typical Performance Characteristics (Continued) VIN=VE/S=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3μH, C1=C3=10μF, C2=C2’=10μF, TA=25°C, unless otherwise specified. 2.60 1.300 2.58 1.275 1.250 2.56 1.225 VO2 Voltage (V) VO1 Voltage (V) 2.54 2.52 2.50 2.48 2.46 1.200 1.175 1.150 1.125 1.100 1.075 2.44 1.050 VO2=1.2V, IO2=1A 2.42 200 400 600 800 1000 VO1=2.5V, IO1=1A 1.025 2.40 1.000 1200 200 Output Current (mA) 400 600 800 1000 1200 1400 Output Current (mA) Figure 8. VO1 Voltage vs. Output Current Figure 9. VO2 Voltage vs. Output Current 100 100 95 95 90 85 85 80 80 75 VO2 Efficiency (%) VO1 Efficiency (%) 90 75 70 65 60 70 65 60 55 50 45 55 40 50 35 30 VO1=2.5V 45 VO2=1.2V 25 40 20 200 400 600 800 1000 1200 200 Output Current (mA) 600 800 1000 1200 1400 Output Current (mA) Figure 10. VO1 Efficiency vs. Output Current May. 2011 400 Figure 11. VO2 Efficiency vs. Output Current Rev. 1.3 BCD Semiconductor Manufacturing Limited 8 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Typical Performance Characteristics (Continued) VIN=VE/S=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3μH, C1=C3=10μF, C2=C2’=10μF, TA=25°C, unless otherwise specified. VIN 2V/div VO1 2V/div V01 2V/div VO2 1V/div VIN 5V/div VPOR 5V/div VO2 1V/div VPOR 2V/div Time 4ms/div Time Figure 12. Start-up from VIN Figure 13. Power-down from VIN IO1 500mA/div I O2 500mA/div VO1 (AC) 100mV/div VO2 (AC) 50mV/div Time 100μs/div Time Figure 14. Load Transient (VO=2.5V IO=0.5A to 1.0A) May. 2011 400μs/div 100μs/div Figure 15. Load Transient (VO=1.2V IO=0.5A to 1.0A) Rev. 1.3 BCD Semiconductor Manufacturing Limited 9 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Typical Performance Characteristics (Continued) VIN=VE/S=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3μH, C1=C3=10μF, C2=C2’=10μF, TA=25°C, unless otherwise specified. Output 1 Induction Current 1A/div Output 1 Induction Current 1A/div VIN 5V/div Output 2 Induction Current 20mA/div VIN 5V/div Output 2 Induction Current 1A/div Time 40μs/div Time Figure 16. Short Protection for Output 1 Figure 17. Short Protection for Output 2 VIN 2V/div VO1 2V/div VO2 2V/div VIN 2V/div VO1 2V/div VO2 2V/div Output 1 Induction Current 1A/div Output 2 Induction Current 1A/div Time May. 2011 40μs/div 10ms/div Time 10ms/div Figure 18. Output 1 Short Recovery Figure 19. Output 2 Short Recovery Rev. 1.3 BCD Semiconductor Manufacturing Limited 10 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Application Information th the POR output transistor is turned off; when off the POR pin is high-Z and may be pulled up high with a resistor. The POR function has built-in deglitching. Once the POR is detected, the power supply outputs will be discharged prior to restart using the soft-start/sequencing routine. 1. Operation The DC-DC converters are current-mode buck converters with a synchronous rectifier and internal compensation. They are designed to be stable with a 1.5μH to 6.8μH inductor value and 10μF to 22μF output capacitor. Both output voltages are resistor programmable. The switching frequency of the converter is fixed and the switches turn on at alternating 180° phase intervals. 5.1Over Current and Short Circuit Protection The DC-DC converters shall have over current and short circuit protection. Under any load condition, at any time, any value of load resistor (including 0Ω) can be applied to the DC-DC outputs instantaneously and held in place indefinitely without the switch current exceeding the peak current limit and without the IC suffering any permanent damage or loss of performance. The output voltage is allowed to drop under over current or short circuit conditions. Recovery to output voltage regulation is required within 10ms of the instant the loading is reduced to maximum allowable rated load; the output voltage shall not exceed the dynamic load excursion limits (±5% excursion) upon recovery. Over current shall not be triggered by a sudden rate of load current change provided the loading does not exceed the output load rating of 1A. The converter operates in 2 possible modes: Continuous Mode (CM), and Pulse Skipping Mode (PSM). CM is the default mode under normal loading. Under light loads, PSM mode occurs, where switching cycles are skipped if the current demand is low. 2. Soft-start The DC-DC converter contains a soft-start function that brings the output voltages up in a slowly increasing ramp with any resistive load from open circuit to 1A (resistive) and any capacitor from 10μF to 22μF. During soft-start, the peak inductor current shall not exceed 750mA until the output voltage reaches 25% of its final value. Current limit shall be active but not trip during soft-start into a rated resistive load. Overshoot voltage during soft-start is limited to 1%. 6. E/S Function Enable/Synchronization function. Pulling this pin high statically enables the AP3421/A/B while pulling the pin low statically for longer than 4μs will shut down the AP3421/A/B. Applying a pulse to this pin will synchronize SW1 and SW2 switching frequency to ½ the external clock frequency. The external frequency lock-in ranges from 1.5MHz to 3.0MHz. 3. Power Sequencing and Enable When power is applied and if E/S input is asserted (High) or is toggling, the DC-DC converters will enter RUN mode after a short settling period. If the E/S pin is a static low, the IC will enter a SLEEP state where it draws very little input current. When in RUN mode, if there is no fault condition, the VO1 output (SW1) will be the first output to begin soft-start. When the reference voltage for FB1 reaches approximately 90% of the final value, the VO2 output (SW2) will begin soft-start. 4. POR Under voltage comparators are provided to monitor the output voltages and VMON which could be the input voltage. If any of these voltages falls below its POR threshold, a POR open drain output will turn on which pulls the POR pin low. After the POR condition is cleared, there is a delay of 20ms before May. 2011 Rev. 1.3 BCD Semiconductor Manufacturing Limited 11 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Typical Application VIN=5V C1' 1 F C1 10 F 84.5k 4.7k PVIN OFF ON VO1=2.5V 30.1k C3 10 F AVIN SW1 24.9k POR E/S L1 3.3 VMON L2 3.3 AGND VO2=1.2V SW2 FB1 PGND FB2 C2 10 F C2' 10 F 4.02k 20k 20k Figure 20. Typical Application Circuit of AP3421 (Note 2) May. 2011 Rev. 1.3 BCD Semiconductor Manufacturing Limited 12 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Typical Application (Continued) VIN=3.3 to 5V C1' 1 F C1 10 F 36k 4.7k PVIN OFF ON VO1=2.5V 30.1k C3 10 F AVIN SW1 18k POR E/S L1 3.3 VMON L2 3.3 AGND VO2=1.2V SW2 FB1 PGND FB2 C2 10 F C2' 10 F 4.02k 20k 20k Figure 21. Typical Application Circuit of AP3421A /B (Note 2) Note 2: AVIN and PVIN pin should not be connected together directly to avoid disturbance between them in PCB layout: 1) Place a 1.0μF capacitor between AVIN pin and AGND for power filtering. 2) Place a 10μF capacitor between PVIN pin and PGND for power filtering. May. 2011 Rev. 1.3 BCD Semiconductor Manufacturing Limited 13 Preliminary Datasheet 1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B Mechanical Dimensions DFN-3×3-10 May. 2011 Rev. 1.3 Unit: mm(inch) BCD Semiconductor Manufacturing Limited 14 BCD Semiconductor Manufacturing Limited http://www.bcdsemi.com IMPORTANT NOTICE IMPORTANT NOTICE BCD Semiconductor BCD Semiconductor Manufacturing Manufacturing Limited Limited reserves reserves the the right right to to make make changes changes without without further further notice notice to to any any products products or or specifispecifications herein. cations herein. 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