EN5364QI-E. Preliminary. Feature Rich 6A Voltage Mode Synchronous Buck PWM DC-DC Converter with Integrated Inductor RoHS Compliant - Halogen Free

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1 Feature Rich 6A Voltage Mode Synchronous Buck PWM DC-DC Converter with Integrated Inductor RoHS Compliant - Halogen Free Description The is a Power Supply on a Chip (PwrSoC) DC to DC converter in a 68 pin QFN module. It has a rich feature set to facilitate ease of use in systems that are sensitive to beat tones. The switching frequency can be synchronized to an external clock or other s with the added capability of phasing multiple s as desired. Other features include precision Enable threshold, pre-bias monotonic start-up, margining and parallel operation. During parallel operation, the phase of switchers can be controlled to minimize ripple. Typical Application Circuit V IN 1Ω 47µF 15nF PVIN VOUT AVIN ENABLE PGND XFB SS PGND AGND Figure 1: Simple Layout. 47µF V OUT is specifically designed to meet the precise voltage and fast transient requirements of present and future high-performance, lowpower processor, DSP, FPGA, ASIC, memory boards and system level applications in a distributed power architecture. Advanced circuit techniques, ultra high switching frequency, and very advanced, high-density, integrated circuit and proprietary inductor technology deliver highquality, ultra compact, non-isolated DC-DC conversion. Operating this converter requires very few external components. The Enpirion integrated inductor solution significantly helps to reduce noise. The complete power converter solution enhances productivity by offering greatly simplified board design, layout and manufacturing requirements. All Enpirion products are RoHS compliant and lead-free manufacturing environment compatible. Ordering Information Part Number Temp Rating ( C) Package -T -40 to pin QFN T&R -E QFN Evaluation Board Features Integrated Inductor, MOSFETS, Controller in a 8 x 11 x 1.85mm package Wide input voltage range of 2.375V to 5.5V. > 20W continuous output power. High efficiency, up to 93%. Output voltage margining Master/slave configuration for paralleling multiple s for greater power output. Programmable phase delay between Master / Slave and Slave / Slave devices for lower output ripple. 5MHz operating frequency with ability to synchronize to an external system clock or other EN5364s. Multiple EN5364s on a system board can be phase locked to eliminate beat frequencies. Programmable phase delays allow reduction of input ripple. Monotonic output voltage ramp during startup with pre-bias loads. Precision Enable pin for accurate sequencing of power converters and Power OK signal. Programmable soft-start time. Soft Shutdown. Thermal shutdown, Over current, short circuit, and under-voltage protection. RoHS compliant, MSL level 3, 260C reflow *Optimized PCB Layout file downloadable from the Enpirion Website to assure first pass design success.

2 Applications Point of load regulation for low-power processors, network processors, DSPs, FPGAs, and ASICs Low voltage, distributed power architectures with 2.5V, 3.3V or 5V rails Computing, broadband, networking, LAN/WAN, optical, test & measurement DSL, STB, DVR, DTV, Industrial PC Beat frequency sensitive applications Applications requiring monotonic start-up with pre-bias Ripple voltage sensitive applications Noise sensitive applications Pin Configuration Below is a top view diagram of the package. Figure 2: Top View of Package NOTE: NC pins are not to be electrically connected to each other or to any external signal, ground, or voltage. However, they must be soldered to the PCB. Failure to follow this guideline may result in part malfunction or damage. 2

3 Pin Descriptions PIN NAME FUNCTION 1-4 PGND Output power ground. Refer to layout section for specific layout requirements VOUT Regulated converter output. Decouple with output filter capacitor to PGND. Refer to layout section for specific layout requirements NC NO CONNECT: These pins should not be electrically connected to each other or to any external signal, voltage, or ground. One or more of these pins may be connected internally SW Output Switching Waveform port PGND Output power ground. Refer to layout section for specific layout requirements PVIN Input power supply. Connect to input power supply. Decouple with input capacitor to PGND. Refer to layout section for specific layout requirements NC NO CONNECT: These pins should not be electrically connected to each other or to any external signal, voltage, or ground. One or more of these pins may be connected internally. 47 PGND Output power ground. Refer to layout section for specific layout requirements. 48 S_OUT Digital Output. Depending on the mode, either a clock signal synchronous with the internal switching frequency or the PWM signal is output on this pin. These signals are delayed by a time that is related to the resistor connected between S_Delay and AGND. 49 S_IN Digital Input. Depending on the mode, this pin accepts either a input clock to phase lock the internal switching frequency to or a PWM input from another. 50 M_S This is a Ternary Input put. Floating the pin disables parallel operation. A low level configures the device as Master and a High level configures the device as a slave. 51 EN_PB This is the Enable Pre-Bias Input. When this pin is pulled high, the Device will support monotonic start-up under a pre-bias load. 52 ENABLE This is the Device Enable pin. A high level enables the device while a low level disables the device. 53 AVIN This is the Input voltage to the controller. A quiet supply! 54 POK Power OK is an open drain transistor for power system state indication. POK is a logic high when VOUT is with -10% to +20% of VOUT nominal. Being a open drain output several devices may be wired to logically AND the function. Size pull-up resistor to limit current to 4mA when POK is low. 55 AGND This is the quiet ground for the controller. 56 XFB This is the External Feedback input pin. A resistor divider connects from the output to AGND. The mid-point of the resistor divider is connected to XFB. The output voltage regulates so as to make the XFB node voltage = 0.600volt. 57 EAOUT Optional Error Amplifier output. Allows for customization of the control loop. 58 NC NO CONNECT: These pins should not be electrically connected to each other or to any external signal, voltage, or ground. One or more of these pins may be connected internally. 59 SS A soft-start capacitor is connected between this pin to AGND. The value of the capacitor controls the soft-start interval. 60 S_DELAY A resistor is connected between this pin and AGND. The value of the resistor controls the delay in S_OUT MAR[1:2] These are 2 ternary input pins. Each pin can be a logical Lo, Logical Hi or Float condition. 7 of the 9 states are used to modulate the output voltage by 0%, ±5%, ±10% or ±15%. The 8th state is used to by-pass the delay in S_OUT. 63 VSENSE This pin senses the output voltage when the device is placed in the Back-feed (or Pre-bias) mode PGND Output power ground. Refer to layout section for specific layout requirements. 3

4 Block Diagram S_OUT S_IN PVIN M_S Digital I/O To PLL UVLO Thermal Limit MAR1/2 Current Limit Over Voltage P-Drive NC(SW) PLL / Sawtooth Generator (-) PWM Comp (+) EAOUT Compensation Network N-Drive V OUT PGND ENABLE Error Amp (-) (+) power Good Logic XFB POK SS Soft Start Reference Voltage selector Bandgap Reference EN_PB EAOUT MAR1 MAR2 Figure 3: System block diagram. 4

5 Absolute Maximum Ratings CAUTION: Absolute Maximum ratings are stress ratings only. Functional operation beyond recommended operating conditions is not implied. Stress beyond absolute maximum ratings may cause permanent damage to the device. Exposure to absolute maximum rated conditions for extended periods may affect device reliability. PARAMETER SYMBOL MIN MAX UNITS Input Supply Voltage V IN V Voltages on: EN, EN_PB -0.5 V IN V Voltage on XFB V Voltages on: EAOUT V Voltages on: SS, PWM, S_IN, S_OUT, MAR[1:2] V Voltages on: POK -0.5 V IN V Storage Temperature Range T STG C Reflow Temp, 10 Sec, MSL3 JEDEC J-STD-020A 260 C ESD Rating (based on Human Body Model) 2000 V Recommended Operating Conditions PARAMETER SYMBOL MIN MAX UNITS Input Voltage Range V IN V Output Voltage Range V OUT 0.60 V IN 0.1*I LOAD V Operating Ambient Temperature T A C Operating Junction Temperature T J C Thermal Characteristics PARAMETER SYMBOL TYP UNITS Thermal Resistance: Junction to Ambient (0 LFM) (Note 1) θ JA 20 C/W Thermal Resistance: Junction to Case (0 LFM) θ JC 1.5 C/W Thermal Overload Trip Point T J-TP +150 C Thermal Overload Trip Point Hysteresis 20 C NOTES: 1. Based on a four-layer board and proper thermal design in line with JEDEC EIJ/JESD 51 Standards. 5

6 Electrical Characteristics NOTE: V IN =5.5V over operating temperature range unless otherwise noted. Typical values are at T A = 25 C. PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS Input Voltage V IN V Output Regulation Feedback Pin 2.375V VIN 5.5V, V Voltage OUT I LOAD = 1A; T A = 25 C V Feedback Pin Voltage V OUT 2.375V V IN 5.5V, 0A I LOAD 6A -40 ºC T A +85 ºC Transient Response (I OUT = 0% to 100% or 100% to 0% of Rated Load) V Peak Deviation V IN = 5V, 1.2V < V OUT < 3.3V OUT C OUT =50uF Output Voltage Ripple Peak-to-peak V OUT-PP C OUT = 5 x 10µF X5R or X7R V IN = 5.0V, V OUT = 1.2V, I OUT = 6A, MLCC Under Voltage Lockout Under Voltage Lock out threshold Switching Frequency Switching Frequency V UVLO V IN Increasing V IN Decreasing V 5 % <20 mv F SWITCH Free Running frequency 5 MHz Phase-Lock Range (Note 3) Phase-Lock PLL Pull range about free running F Frequency range PLL frequency MHz S_IN Duty Cycle for SYNC SY DC M_S Pin Float or Low % S_IN Duty Cycle for PWM SY DC M_S Pin High % Phase-Delay (Note 3) Phase Delay between S_IN and Φ DEL Phase delay programmable via resistor connected from S_Delay to ns S_OUT AGND. Phase Delay between S_IN and Φ DEL Delay By-Pass Mode 10 ns S_OUT Phase Delay Accuracy % Phase Delay vs. S_Delay Resistor value Load Characteristics Maximum Continuous Output Current Current Limit Threshold Supply Current Φ DEL Delay in nsec / kω Delay in phase angle / kω 5MHz switching frequency I OUT (Note 1) 6 A I OCP The OCP Trip level 13.5 A V ns 6

7 Pre-Bias Level V PB Shut-Down Supply Current I S ENABLE=0V 250 µa Precision Enable Operation Max voltage to ensure the Disable Threshold V DISABLE converter is disabled 1.0 V Enable Threshold V ENABLE 2.375V V IN 5.5V V Enable Pin Current I EN V IN = 5.5V 50 µa Thermal Shutdown Thermal Shutdown T SD Silicon junction temperature 150 C Hysteresis 20 C Pre-Bias Start-Up programmed output voltage for % Allowable Pre-Bias as a fraction of monotonic start up Non-Monotonicity V PB_NM Allowable non monotonicity 50 mv Power OK/GOOD V OUT Range for P OK = High P OK Deglitch Delay V POK Logic Low level V POK Logic High level Parallel Mode Operation Range of output voltage as a fraction of programmed value when POK is asserted. (Note 2) Falling edge deglitch delay after output crossing 90% level % 50 us With 4mA current sink into P OK pin 0.4 V Current Balance I OUT the difference between any 2 parts. With 2 4 converters in parallel, V IN < 50mV; R TRACE < 10mΩ. V IN V +/-10 % Output Rise Time V OUT Rise Time Accuracy Logic Levels Ternary Logic Low Threshold Ternary Logic High Threshold Binary Logic Low Threshold Binary Logic High Threshold Ternary pin Input Current T RISE T RISE = C ss * 65KΩ; 10nF C SS 30nF (Notes 3, 4) % V T-Low Threshold voltage for Logic Low 0.4 V V T-High Threshold voltage for Logic High (internally pulled high; can be left floating to achieve logic high) V V B-Low 0.8 V B-High 1.8 I ITERN The ternary pin has 100kΩ to AGND and another 100kΩ to an internal 2.5V supply. It is voltage clamped to ~2V. If connecting to VIN recommend using a series resistor. See Figure-5 See Figure-5 µa 7

8 NOTES: 1. Maximum output current may need to be de-rated, based on operating condition, to meet T J requirements. 2. POK threshold when V OUT is rising is nominally 92%. This threshold is 90% when V OUT is falling. After crossing the 90% level, there is a 256 clock cycle (~50us) delay before POK is de-asserted. The 90% and 92% levels are nominal values. Expect these thresholds to vary by ±3%. 3. Parameter not production tested but is guaranteed by design. 4. Rise time begins when AVIN > V UVLO and Enable=HIGH. Features Precision Enable Threshold: The Enable threshold is a precision Analog voltage rather than a digital logic threshold. Precision threshold along with choice of soft-start capacitor helps to accurately sequence multiple power supplies in a system. Margining: The nominal output voltage can be increased / decreased by 5, 10 or 15% for system compliance, reliability or other tests. The POK threshold voltages scale with the margined output voltages. The following table provides truth table. MAR-1 MAR-2 Output Modulation Changes planned to values listed below Float Float 0% Low Low -5% High Low +5% Low High -10% High High +10% Low Float -15% High Float +15% Float High Delay By-Pass Float Low Reserved Table 1: Margining Truth Table Pre-Bias Operation: When Device EN_PB is asserted, the device will support a monotonic output voltage ramp with the output capacitor charged to a pre-bias level. Proprietary circuit ensures the output voltage ramps monotonically from pre-bias voltage to the programmed output voltage. Monotonic start-up is guaranteed for pre-bias voltages between 20% and 85% of the programmed output voltage. Phase-Lock Operation: With M_S pin floating or at a logical 0, the internal switching clock of the DC/DC converter can be phase-locked to a clock signal applied to S_IN. The clock logic levels are <0.4V and >2.0V. The clock frequency should be within ±10% of the free running frequency. A delayed copy of the internal switching clock is available at S_OUT. The magnitude of delay is controlled by the value of the resistor connected between S_Delay and AGND pins. Multiple devices on a system board may be daisy chained to reduce or eliminate input ripple as well as avoiding beat frequency components. Master / Slave Operation: Multiple devices may be connected in a Master / Slave configuration to handle very large load currents. One Master device can directly control up to 4 Slave devices or one Master device may control any number of Slave devices in a daisy chain. The Master device s switching clock may be phase-locked to an external clock source or another. The device is set in Master mode by pulling the M_S pin low or in Slave mode by pulling M_S pin high. When this pin is in Float state, parallel operation is not possible. In master mode, the internal PWM signal 8

9 is output on the S_OUT pin. The PWM signal at S_OUT is delayed relative to the Master device s internal PWM signal. (The magnitude of delay is controlled by the value of the resistor connected between S_Delay and AGND pins.) This PWM signal from the Master can be fed to one or more Slave devices at its S_IN input. The Slave device acts like an extension of the power FETs in the Master. The inductor in the slave prevents crow-bar currents from Master to slave due to timing delays. The Slave device puts out its own delayed PWM on S_OUT which could feed the next device in the daisy chain. As a practical matter, paralleling more than 4 devices may be very difficult from the view point of maintaining very low impedance in VIN and VOUT lines. Phase Delay: When multiple s are used on a board, the phase delay function may be used advantageously for reducing input / output ripple. The phase delay can be used in two ways. First, the s can all be phase locked by feeding the S_OUT of one device into the S_IN of the next device in a daisy chain. All the switchers are now switching at a common frequency. However, the phase delay among the switching waveforms may be controlled by an appropriate choice of a resistor that is connected from the pin S_Delay to AGND. The magnitude of this delay is approximately 2ns/kΩ or 3.5 /kω (@5MHz) of resistance subject to a minimum / maximum delay as given in the table of electrical characteristics. Second, when multiple s are used in parallel to support a large load, one device acts as a master device whose PWM output is fed to other s operating as slaves. Although all the devices are switching at the same frequency and duty cycle, their phases can be controlled by an appropriate choice for S_Delay resistor. The Master / Slave parallel mode operation is described in more detail in a separate application note. Over Current Protection: When the load current exceeds the over current protection trip level the power FETs are placed in a high impedance state and the device enters a hiccup mode. The output is disabled for 8192 clock cycles (~1.6ms) followed by a normal soft-start. The device remains in hiccup mode as long as the fault persists. Power OK / Good: Power good (POK) signal is asserted when the output voltage is between 90% and 120% of the nominal. When V OUT is rising the POK threshold is nominally at 92% of steady state V OUT. When V OUT is falling, the nominal threshold is 90% of steady state voltage. If V OUT exceeds 120% of programmed value, POK is deasserted and the power NFET is turned on. This event could cause the input power supply to to enter a over current condition. Soft-start circuit: to limit the in-rush current when the converter is powered up. The soft-start interval is programmable through choice of Soft-start capacitance. Thermal shutdown: When the device gets beyond the safe operating temperature, the output is shutdown. Adequate hysteresis is provided to prevent chatter at trip point. Under-voltage lockout: UVLO circuit disables the converter output when the input voltage is less than approximately 2.2V to ensure that operation does not begin before there is adequate voltage to properly bias all internal circuitry. 9

10 Output Voltage Setting / Phase-Lead Capacitor Details VOUT RA = 30,000* Vin ( value in Ω) RA CA XFB CA = 4 6.9*10 * Cout RA ( Cout & CA in Farads, RA in Ω) RB AGND RB = V out 6 RA Figure 4: Output voltage resistor divider and phase-lead capacitor calculation. The above formulas ensure optimum loop bandwidth for any Vin and Vout combination. The equations need to be followed in the order written above. 2.5V VIN Rext 100k Vf ~ 2V D1 R1 100k R2 100k To Gates Maximum value of Rext = (VIN -2)*67k Input pin current = (VIN-2)/Rext R3 7k AGND Figure 5: Figure shows means to select Rext value to be used when connecting MAR-1, MAR-2 and / or M_S pins to VIN. 10

11 Phasing Multiple s (An Example) P/AVIN X1 X1_1 X1_2 XFB P/AVIN VOUT VOUT1 VOUT2 VOUT3 XFB VOUT XFB VOUT C1 P/AVIN C11 P/AVIN C21 EXT_CLK (Optional) S_DELAY S_IN P/AGND S_OUT R1 S_DELAY S_IN P/AGND S_OUT R11 S_DELAY S_IN P/AGND S_OUT R21 CO1 CO2 CO3 R3 R13 R23 R2 R12 R22 P/AGND Figure 6: Example of Synchronizing multiple s in a daisy chain with phase delay. V DRAIN - 1 Delay ~ 140 V DRAIN - 2 Delay ~ 120 V DRAIN - 3 Figure 7: Example of a possible way to synchronize and use delays advantageously to minimize input ripple. R3 ~ 39kΩ, R13 ~ 33kΩ. (Refer to Figure 6 for R3 and R13.) 11

12 Typical Performance Characteristics Efficiency Efficiency Efficiency (% ) Efficiency (% ) Load (Amps) Load (Amps) Efficiency vs. Load: V IN = 3.3V; VOUT = 2.5, 1.2V Efficiency vs. Load: V IN = 5.0V; V OUT = 3.3, 2.5, 1.2V Start-up waveform: V IN = 5.5V, V OUT = 3.3V, Load = 6A Ch.1 Enable, Ch.2 V OUT, Ch.3 - POK Start-up waveform: V IN = 5.5V, V OUT = 1.2V, Load = 6A Ch.1 Enable, Ch.2 V OUT, Ch.3 POK Output Ripple: V IN = 5.0V, V OUT = 1.2V, C OUT = 1x47uF (1206) + 1x10uF (0805) Output Ripple: V IN = 3.3V, V OUT = 1.2V, C OUT = 1x47uF (1206) + 1x10uF (0805) 12

13 Load Transient: 0-6A Step. V IN = 5.0V, V OUT = 1.2V Load Transient: 0-6A Step. V IN = 3.3V, V OUT = 1.2V Start-up waveform in Back-feed (Pre-bias mode) Start-up waveform in Back-feed (Pre-bias mode) V BF = 400mV, V OUT = 2.5V V BF = 1.9V, V OUT = 2.5V Delay vs. S_Delay Resistance Delay (ns) S_Delar R (kohm) Series1 Delay vs. S_Delay Resistance 13

14 Theory of Operation Synchronous Buck Converter The is a synchronous, programmable power supply with integrated power MOSFET switches and integrated inductor. The nominal input voltage range is V. The output voltage is programmed using an external resistor divider network. The feedback control loop is a type III, voltage-mode and the device uses a lownoise PWM topology. Up to 6A of continuous output current can be drawn from this converter. The 5MHz operating frequency enables the use of small-size input and output capacitors. The power supply has the following protection features: Over-current protection with hiccup mode. Short Circuit protection. Thermal shutdown with hysteresis. Under-voltage lockout circuit to disable the converter output when the input voltage is less than approximately 2.2V Output Voltage Programming The EN5364 output voltage is programmed using a simple resistor divider network. A phase lead capacitor is required for stabilizing the loop. Figure 4 shows the required components and the equations to calculate their values. The EN5364 output voltage is determined by the voltage presented at the XFB pin. This voltage is set by way of a resistor divider between V OUT and AGND with the midpoint going to XFB. Input Capacitor Selection The requires between 40-80uF of input capacitance. Low ESR ceramic capacitors are required with X5R or X7R dielectric formulation. Y5V or equivalent dielectric formulations must not be used as these lose capacitance with frequency, temperature and bias voltage (please see Table 2). In some applications, lower value ceramic capacitors maybe needed in parallel with the larger capacitors in order to provide high frequency decoupling. Output Capacitor Selection The has been optimized for use with output capacitance between 47µF and 150µF. The phase lead capacitor value depends on the the output capacitance as shown in Figure-4. Low ESR ceramic capacitors are required with X5R or X7R dielectric formulation. Y5V or equivalent dielectric formulations must not be used as these lose capacitance with frequency, temperature and bias voltage (please see Table 3). Description MFG P/N 47uF, 10V, X5R, uF, 6.3V, X5R, 1206 Taiyo Yuden Taiyo Yuden Murata LMK316BJ476ML-T JMK316BJ476ML-T GRM31CR60J476ME19L 22uF, 6.3V, X7R, 1206 Taiyo Yuden Murata JMK316B7226ML-T GCM31CR70J226KE23L Description MFG P/N 47uF, 10V, X5R, 1206 Taiyo Yuden LMK316BJ476ML-T 10uF, 10V, X7R, 0805 Taiyo Yuden Murata LMK212C106KG-T GRM21BR71A106KE51L 22uF, 10V, X5R, 1206 Taiyo Yuden Murata LMK316BJ226ML-T GRM31CR61A226ME19L Table 2: Recommended input capacitors. 14 Table 3: Recommended output capacitors. Output ripple voltage is primarily determined by the aggregate output capacitor impedance. At the 5MHz switching frequency output impedance,

15 denoted as Z, is comprised mainly of effective series resistance, ESR, and effective series inductance, ESL: Z = ESR + ESL. Placing multiple capacitors in parallel reduces the impedance and hence will result in lower ripple voltage. 1 Z 1 = Z 1 + Z Total 1 2 Z n Typical ripple versus capacitor arrangement is given below: Output Capacitor Configuration Typical Output Ripple (mvp-p) (as measured on Evaluation Board) 1x47uF + 1x10uF <30 5 x 10 uf <20 Table 4. Output ripple vs capacitor configuration. Compensation The EN5364 uses of a type III compensation network. Most of this network is integrated. However a phase lead capacitor is required in parallel with upper resistor of the external feedback network (see Figure 4). Total compensation is optimized for use with a minimum of 47µF output capacitance and will result in a wide loop bandwidth and excellent load transient performance for most applications. The equations shown in Figure 4 are valid for Cout up to 150µF at the voltage sensing point. Additional capacitance may be placed beyond the voltage sensing point outside the control loop. Voltage mode operation provides high noise immunity at light load. Further, Voltage mode control provides superior impedance matching to ICs processed in sub 90nm technologies. In exceptional cases modifications to the compensation may be required. The provides the capability to modify the control loop response to allow for customization for specific applications. For more information, contact Enpirion Applications Engineering support. 15 Enable Operation The ENABLE pin provides a means to start normal operation or to shut down the device. The Enable threshold is precisely set by a voltage reference. This allows precision sequencing of multiple s. When the ENABLE pin is asserted high, the device will undergo a normal soft start. As the output voltage ramps up (ramp rate controlled by choice of soft-start capacitor) a second device may be Enabled using this ramp. The second device will start up after a well defined time given by the ramp rate and the precise threshold level. Soft-Start Operation The SS pin in conjunction with a small external capacitor between this pin and AGND provides the soft start function to limit the in-rush current during start-up. During start-up of the converter the reference voltage to the error amplifier is gradually increased to its final level by an internal current source of typically 10uA charging the soft start capacitor. The typical soft-start time for the output to reach regulation voltage, from when AVIN > V UVLO and Enable crosses its logic high threshold, is given by: T SS = C SS * 65KΩ (seconds) Where the soft-start time T SS is in seconds and the soft-start capacitance C SS is in Farads. Typically, a capacitor of around 15nF is recommended. A proper choice of SS capacitance can be used advantageously for power supply sequencing using the precision Enable threshold. During a soft-start cycle, when the soft-start capacitor voltage reaches 0.60V, the output has reached its programmed regulation range. Note that the soft-start current source will continue to charge the SS capacitor beyond 0.6V. During normal operation, the soft-start capacitor will charge to a final value of ~1.5V. Soft Shutdown When the Enable signal is de-asserted, the soft-

16 start capacitor is discharged in a controlled manner. Thus the output voltage ramps down gradually. The internal circuits are kept active for the duration of soft-shutdown, thereafter they are deactivated. POK Operation The POK signal is an open drain signal from the converter indicating the output voltage is within the specified range. The POK signal is asserted when the rising output voltage crosses 92% (nominal) of the programmed output voltage. POK is de-asserted ~50us (256 clock cycles) after the falling output voltage crosses 90% (nominal) of the programmed voltage. POK is also de-asserted if the output voltage exceeds 120% of the programmed output. If the feedback loop is broken, POK will remain de-asserted (output < 92% of programmed value!) but the output voltage will equal the input voltage. If however, there is a short across the PFET, and the feedback is in place, POK will be de-asserted as a over voltage condition. Also, the power NFET is turned on resulting in a large input supply current. This is turn is expected to trip the OCP of the power supply powering the. Over-Current Protection The current limit function is achieved by sensing the current flowing through a sense P-FET. When the sensed current exceeds the current limit, both NFET and PFET switches are turned off. If the over-current condition is removed, the over-current protection circuit will re-enable the PWM operation. If the over-current condition persists, the circuit will continue to protect the load. The OCP trip point is nominally set to 225% of maximum rated load. In the event the OCP circuit trips, the device enters a hiccup mode. The device is disabled for ~1.6msec and restarted with a normal soft-start. This cycle can continue indefinitely as long as the over current condition persists. Thermal Overload Protection Thermal shutdown will disable operation when the Junction temperature exceeds approximately 150ºC. Once the junction temperature drops by approx 20ºC, the converter will re-start with a normal soft-start. Input Under-Voltage Lock-Out POK is an open drain output. It requires an external pull up. Multiple s POK pins may be wired NOR with a single pull up. The open drain NFET is designed to sink up to 4mA. The pull-up resistor value should be chosen to limit the current from exceeding this value when POK is logic low. Over-Voltage Protection There is no over voltage protection caused by a open at XFB node. When the input voltage is below a required voltage level (V UVLO ) for normal operation, the converter switching is inhibited. The lock-out threshold has hysteresis to prevent chatter. Parallel Device Operation The is capable of paralleling up to a total of four converters to provide up to 24A of continuous current. Please refer to the Parallel Operation Application note, available on the Enpirion website, for details on parallel operation. 16

17 Layout Recommendations Under Development Figure 8: Layout of power and ground copper. Recommendation 1: Input and output filter capacitors should be placed as close to the package as possible to reduce EMI from input and output loop currents. This reduces the physical area of the Input and Output AC current loops. Recommendation 2: Place a slit in the input/output capacitor ground copper starting just below the common connection point of the device GND pins as shown in figures 8 and 9. Recommendation 3: The large thermal pad underneath the component must be connected to the system ground plane through as many vias as possible. The drill diameter of the vias should be less than 0.33mm, and the vias must have at least 1 oz. copper plating on the inside wall, making the finished hole size around 0.26mm. This connection provides the path for heat dissipation from the converter. Please see figures: 9, 10 and 11. Recommendation 4: Multiple small vias should be used to connect ground terminal of the input capacitor and output capacitors to the system ground plane as shown in figure 6. Figure 9: Use of thermal & noise suppression vias. These vias can be the same size as the thermal vias discussed in recommendation 3. Recommendation 5: The system ground plane referred to in recommendations 3 and 4 should be the first layer immediately below the surface layer. This ground plane should be continuous and un-interrupted below the converter and the input/output capacitors shown in figure 8. Recommendation 6: As with any switch-mode DC/DC converter, do not run sensitive signal or control lines underneath the converter package. Please refer to the Gerber files and summarized layout notes available on the Enpirion website for more layout details. NOTE: Figures 8 and 9 show only the critical components and traces for a minimum footprint layout. ENABLE, Vout-programming, and other small signal pins need to be connected and routed according to the specific application. 17

18 Design Considerations for Lead-Frame Based Modules Exposed Metal on Bottom of Package Lead frame offers many advantages in thermal performance, in reduced electrical lead resistance,, and in overall foot print. However, they do require some special considerations. In the assembly process lead frame construction requires that, for mechanical support, some of the lead-frame cantilevers be exposed at the point where wire-bond or internal passives are attached. This results in several small pads being exposed on the bottom of the package. Only the large thermal pad and the perimeter pads are to be mechanically or electrically connected to the PC board. The PCB top layer under the should be clear of any metal except for the large thermal pad. The grayed-out area in Figure 7 represents the area that should be clear of any metal (traces, vias, or planes), on the top layer of the PCB. Figure 8 demonstrates the recommended PCB footprint for the. Figure 9 shows the shape and location of the exposed metal pads as well as the mechanical dimension of the large thermal pad and the pins. Figure 10: Lead-Frame exposed metal. Grey area highlights exposed metal that is not to be mechanically or electrically connected to the PCB. 18

19 Figure 11: Recommended footprint for PCB. 19

20 Package Dimensions Figure 12. Package dimensions. 20

21 Contact Information Enpirion, Inc. 685 Route 202/206 Suite 305 Bridgewater, NJ Phone: Fax: Enpirion reserves the right to make changes in circuit design and/or specifications at any time without notice. Information furnished by Enpirion is believed to be accurate and reliable. Enpirion assumes no responsibility for its use or for infringement of patents or other third party rights, which may result from its use. Enpirion products are not authorized for use in nuclear control systems, as critical components in life support systems or equipment used in hazardous environment without the express written authority from Enpirion. 21