1、 1 /a85T High Efficiency 1MHz 2A Synchronous Step Down Regulator Pin Assignments S5 Package (SOT-23-5) (Marking)21 345FBEN GND LXVINFigure 1. Pin Assignment of SC5832A Ordering Information SOT-23-5 Marking Part Number Product Code SC5832AS5C fiW Description The SC5832A is a high efficiency, high fre
2、quency synchronous DC-DC step-down converter. The 100% duty cycle feature provides low dropout operation, extending battery life in portable systems. The internal synchronous switch increases efficiency and eliminates the need for external Schottky diode. At shutdown mode, the input supply current i
3、s less than 1A. The current limit protection and on-chip thermal shutdown features provide protection against any combination of overload or ambient temperature. Features Low RDS(ON) for Internal Switch (Top/Bottom): 180/100m 2.5V6.5V Input Voltage Range 2A Output Current 1MHz Switching Frequency Mi
4、nimizes the External Components Internal Soft-Start Limits the Inrush Current Internal Compensation Function 100% Dropout Operation RoHS Compliant and Halogen Free SOT-23-5 Applications Set Top Box LCD TV Tablet Portable Equipment SC5832A C: Green TR: Tape/Reel Package Type S5: SOT-23-5 深圳市中广芯源科技有限公
5、司SC5832ATEL:0755-27668758/29469758 web:http:/ 2 /a85T Typical Application Circuit Figure 2. Schematic Diagram VOUT C1 R1 R2 L1 C2 3.3V 10F MLCC 453k 100k H 22F MLCC 2.5V 10F MLCC 316k 100k H 22F MLCC 1.8V 10F MLCC 200k 100k 1.8H 22F MLCC 1.5V 10F MLCC 150k 100k 1.5H 22F MLCC 1.2V 10F MLCC 100k 100k
6、1.5H 22F MLCC 1.05V 10F MLCC 75k 100k 1.2H 22F MLCC Table 1. Recommended Component Values SC5832NCEN深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 3 /a85T Functional Pin Description Pin Name Pin No. (SOT-23-5) Pin Function EN 1 Enable Control. Pull high to turn the IC on, and pull low to
7、disable the IC . Don t leave this pin floating. GND 2 Ground Pin. LX 3 Power Switching Output. Connect an inductor to the drains of internal high side PMOS and low side NMOS . VIN 4 Power Supply Input Pin. Drive VIN pin by 2.5V to 6.5V voltage to power on the chip. FB5Voltage Feedback Input Pin. Con
8、nect FB and VOUT with a resistive voltage divider. This IC senses feedback voltage via FB and regulatesit at 0.6V.Block Diagram EASoftStartCOMPCompensationEnableControlSlope CompensationControl Logic Current LimitLogicControland DriverLogicOscillatorUndervoltageLockoutBias SupplyCOMPFBGNDLXVINEN1XVR
9、EF1MFigure 3. Block Diagram of SC5832A 深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 4 /a85T Absolute Maximum Ratings(Note 1) VIN to GND - -0.3V to +6.5V LX to GND - -0.3V to (VIN+0.3) EN, FB, PG to GND - -0.3V to VIN Package hermal esistance, (JA) SOT-23-5 - +250C/W Package hermal esist
10、ance, (JC) SOT-23-5 - +130C/W Maximum Junction Temperature (TJ) - +150C Lead Temperature (Soldering, 10 sec.) - +260C Storage Temperature (TSTG) - -65C to +150 Note 1： Stresses beyond those listed under “Absolute Maximum atings“ may cause permanent damage to the device Recommended Operating Conditio
11、ns (Note 2) Supply Voltage (VIN) - +2.5V to +5.5V Junction Temperature Range - -40C to +125C Ambient Temperature Range - -40C to +85C Note 2： The device is not guaranteed to function outside its operating conditions.深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 5 /a85T Electrical Charact
12、eristics (VIN=5V, TA=25C, unless otherwise specified.) Parameter Symbol Conditions Min Typ Max Unit Input Voltage Range VIN 2.5 5.5 V Shutdown Current ISHDN EN=GND 0.1 1 A Quiescent Current Iq VFB=0.65V, IOUT=0A 80 A Reference Voltage VREF 0.588 0.6 0.612 V FB Input Leakage Current IFB VFB=VIN 0.01
13、1 A P-Channel MOSFET On-Resistance (Note 3) RDS(ON) 180 m N-Channel MOSFET On-Resistance (Note 3) RDS(ON) 100 m P-Channel Current Limit (Note 3) ILIM 2.1 A EN High-Level Input Voltage VIH 1.5 V EN Low-Level Input Voltage VIL 0.4 V Under Voltage Lockout Voltage UVLO 2.4 V UVLO Hysteresis VHYS 0.2 V O
14、scillation Frequency FOSC IOUT=500mA 0.8 1 1.2 MHz Minimum On Time 50 ns Maximum Duty Cycle 100 % VOUTDischarge Resistance100Thermal Shutdown Temperature(Note3)TSD150CInternal Soft Start TimeTSS1msNote 3： Guarantee by design. 深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 6 /a85T Typical
15、Performance Curves Figure 4. Efficiency vs. Load Current Figure 5. Efficiency vs. Load Current Figure 6. Feedback Voltage vs. Temperature Figure 7. Frequency vs. Temperature 65 70 75 80 85 90 95 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Efficiency (%) Load Current (A) VIN=3.3V VIN=5V 70 75 80 85 90 95 1
16、00 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Efficiency (%) Load Current (A) VIN=4.2V VIN=5V 588 591 594 597 600 603 606 609 612 -40 -20 0 20 40 60 80 100 FeedbackVoltage(mV)Temperature (C) 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 -40 -20 0 20 40 60 80 100 Frequency (MHz) Temperature (C) VOUT=1.2V VOUT=3.3
17、V VIN=5V IOUT=0.5A VIN=5V IOUT=0.5A 深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 7 /a85T Function Description The SC5832A is a high efficiency, internal compensation and constant frequency current mode step-down synchronous DC/DC converter. It has integrated high-side (180m, typ) and lo
18、w-side (100m, typ) power switches, and provides 2A continuous load current. It regulates input voltage from 2.5V to 5.5V, and down to an output voltage as low as 0.6V. Control Loop Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for superior load
19、, line response, protection of the internal main switch and synchronous rectifier. The SC5832A switches at a constant frequency (1MHz) and regulates the output voltage. During each cycle, the PWM comparator modulates the power transferred to the load by changing the inductor peak current based on th
20、e feedback error voltage. During normal operation, the main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. When the main switch is off, the synchronous rec
21、tifier will be turned on immediately and stay on until next cycle starts. Enable The SC5832A EN pin provides digital control to turn on/off the regulator. When the voltage of EN exceeds the threshold voltage, the regulator will start the soft start function. If the EN pin voltage is below the shutdo
22、wn threshold voltage, the regulator will turn into the shutdown mode and the shutdown current will be smaller than A. For auto start-up operation, connect EN to VIN. Soft Start The SC5832A employs internal soft start function to reduce input inrush current during start up. The internal soft start ti
23、me will be 1ms. Under Voltage Lockout When the SC5832A is power on, the internal circuits will be held inactive until VIN voltage exceeds the UVLO threshold voltage. And the regulator will be disabled when VIN is below the UVLO threshold voltage. The hysteretic of the UVLO comparator is 200mV (typ).
24、 Short Circuit Protection The SC5832A provides short circuit protection function to prevent the device damaged from short condition. When the short condition occurs and the feedback voltage drops lower than 40% of the regulation level, this will activate the latch protection circuit. Then output wil
25、l be forced shutdown to prevent the inductor current runaway and to reduce the power dissipation within the IC under true short circuit conditions. Once the short condition is removed, reset EN or VIN to restart IC. Over Current Protection The SC5832A over current protection function is implemented
26、by using cycle-by-cycle current limit architecture. The inductor current is monitored by measuring the high-side MOSFET series sense resistor voltage. When the load current increases, the inductor current will also increase. When the peak inductor current reaches the current limit threshold, the out
27、put voltage will start to drop. When the over current condition is removed, the output voltage will return to the regulated value. Over Temperature Protection The SC5832A incorporates an over temperature protection circuit to protect itself from overheating. When the junction temperature exceeds the
28、 thermal shutdown threshold temperature, the regulator will be shutdown. And the hysteretic of the over temperature protection is 30C (typ). 深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 8 /a85T Application Information Output Voltage Setting The output voltage VOUT is set by using a resi
29、stive divider from the output to FB. The FB pin regulated voltage is 0.6V. Thus the output voltage is: Table 2 lists recommended values of R1 and R2 for most used output voltage. Table 2 Recommended Resistance Values VOUT R1 R2 3.3V 453k 100k 2.5V 316k 100k 1.8V 200k 100k 1.5V 150k 100k 1.2V 100k 10
30、0k Place resistors R1 and R2 close to FB pin to prevent stray pickup. Input Capacitor Selection The use of the input capacitor is filtering the input voltage ripple and the MOSFETS switching spike voltage. Because the input current to the step-down converter is discontinuous, the input capacitor is
31、required to supply the current to the converter to keep the DC input voltage. The capacitor voltage rating should be 1.25 to 1.5 times greater than the maximum input voltage. The input capacitor ripple current RMS value is calculated as: ( MS) Where D is the duty cycle of the power MOSFET. This func
32、tion reaches the maximum value at D=0.5 and the equivalent RMS current is equal to IOUT/2. The following diagram is the graphical representation of above equation. A low ESR capacitor is required to keep the noise minimum. Ceramic capacitors are better, but tantalum or low ESR electrolytic capacitor
33、s may also suffice. Output Capacitor Selection The output capacitor is used to keep the DC output voltage and supply the load transient current. When operating in constant current mode, the output ripple is determined by four components: PPL t PPL C t PPL S t PPL ( SL) t S t The following figures sh
34、ow the form of the ripple contributions. VRIPPLE(ESR)(t) + VRIPPLE(ESL) (t) + VRIPPLE(C) (t) + VNOISE (t) = VRIPPLE(t) 0 0.2 0.4 0.6 0.8 1 1.2 10 20 30 40 50 60 70 80 90 I IN(RMS) (A)D (%) (t) (t) (t) (t) 0.5A 1A 2A 深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 9 /a85T Application Inform
35、ation (Continued) PPL ( S ) FSC LS PPL ( SL) SLL SL PPL (C) FSC L C Where FOSC is the switching frequency, L is the inductance value, VIN is the input voltage, ESR is the equivalent series resistance value of the output capacitor, ESL is the equivalent series inductance value of the output capacitor
36、 and the COUT is the output capacitor. Low ESR capacitors are preferred to use. Ceramic, tantalum or low ESR electrolytic capacitors can be used depending on the output ripple requirements. When using the ceramic capacitors, the ESL component is usually negligible. It is important to use the proper
37、method to eliminate high frequency noise when measuring the output ripple. The figure shows how to locate the probe across the capacitor when measuring output ripple. Remove the scope probe plastic jacket in order to expose the ground at the tip of the probe. It gives a very short connection from th
38、e probe ground to the capacitor and eliminates noise. Inductor Selection The output inductor is used for storing energy and filtering output ripple current. But the trade-off condition often happens between maximum energy storage and the physical size of the inductor. The first consideration for sel
39、ecting the output inductor is to make sure that the inductance is large enough to keep the converter in the continuous current mode. That will lower ripple current and result in lower output ripple voltage. The L is inductor peak-to-peak ripple current: L FSC LThe following diagram is an example to
40、graphically represent L equation. VOUT=1.2V, FOSC=1MHz A good compromise value between size and efficiency is to set the peak-to-peak inductor ripple current L equal to 30% of the maximum load current. But setting the peak-to-peak inductor ripple current L between 20%50% of the maximum load current
41、is also acceptable. Then the inductance can be calculated with the following equation: L (MA ) L F SC LTo guarantee sufficient output current, peak inductor current must be lower than the SC5832 high-side MOSFET current limit. The peak inductor current is shown as below: P A (MA ) L 0 0.1 0.2 0.3 0.
42、4 0.5 0.6 0.7 0.8 0.9 2.5 3 3.5 4 4.5 5 5.5 IL (A) VIN (V) Ceramic Capacitor VOUT GND Probe Ground L=2.2H L=1.2H L=1.5H 深圳市中广芯源科技有限公司SC5832ATEL:0755-27668758/29469758 web:http:/ 10 /a85T Application Information (Continued) Feedforward Capacitor Selection Internal compensation function allows users s
43、aving time in design and saving cost by reducing the number of external components. The use of a feedforward capacitor C3 in the feedback network is recommended to improve transient response or higher phase margin. SC5832AVOUTFBR1R2C3For optimizing the feedforward capacitor, knowing the cross freque
44、ncy is the first thing. The cross frequency (or the converter bandwidth) can be determined by using a network analyzer. When getting the cross frequency with no feedforward capacitor identified, the value of feedforward capacitor C3 can be calculated with the following equation: C FC SSWhere FCROSS
45、is the cross frequency. To reduce transient ripple, the feedforward capacitor value can be increased to push the cross frequency to higher region. Although this can improve transient response, it also decreases phase margin and causes more ringing. In the other hand, if more phase margin is desired, the feedforward capacitor value can be decreased to push the cross frequency to lower region. In general, the feedfo
