PT4484—48V 100-W 20-A Programmable Isolated DC/DC Converter SLTS109B (Revised 6/20/2002) Features • 36V to 75V Input Voltage Range • Programmable Output Voltage Range: 4.6V to 5.7V • -40° to +85°C Operating Temp • 1500 VDC Isolation • 90% Efficiency • On/Off Inhibit • Differential Remote Sense • 40A Output with PT4498 • • • • • • Over-Current Protection Over-Temperature Protection Over-Voltage Protection Space-Saving Package Solderable Copper Case Safety Approvals: UL 60950 CSA 22.2 950 VDE EN60950 Pending Description Ordering Information Pin-Out Information The PT4484 Excalibur™ DC/DC converter module combines state-of-theart power conversion technology with un-paralleled flexibility. Incorporating high efficiency and ultra-fast transient response, these modules provide up to 20A of output current over the programmable voltage range of 4.6V to 5.7V. The modules include a number of inbuilt features to facilitate system integration. These include a foldback output current limit, over-temperature protection, and an inhibit on/off control. A differential remote sense is also provided to compensate for voltage drop between the converter and load. For additional output current, one PT4484 may be operated with up to two PT4498 compatible booster modules. Each PT4498 adds an additional 20A of output current capability. PT4484o = 4.6 to 5.7 Volts PT4498o = 20-A Booster Pin PT Series Suffix (PT1234 x ) Case/Pin Configuration Order Suffix Package Code * N A C Vertical Horizontal SMD (EKD) (EKA) (EKC) * Previously known as package styles 1200, 1210, and 1215. (Reference the applicable package code drawing for the dimensions and PC board layout) Function Pin Function 1 +Vin 14 –Vout 2 –Vin 15 –Vout 3 Inhibit 16 –Vout 4 Vr † 17 –Vout 5 Va † 18 –Vout 6 Do not connect 19 –Vout 7 (+)Remote Sense 20 (–)Remote Sense 8 +Vout 21 Do not connect 9 +Vout 22 VID1 10 +Vout 23 VID2 11 +Vout 24 VID3 12 +Vout 25 VID4 13 +Vout 26 DRV † † Pins 4, 5, & 26 are used for booster applications. For stand-alone operation, leave open circuit. • Shaded functions indicate those pins that are referenced to primary-side potential. Standard Application + V IN 1 2 + C1 C2 + V in – V in Inhibit 3 + V OUT 7 + V sns + V out 8-13 PT4484 -V out VID1 - VID4 22 23 24 25 -V sns • Co = Optional 150µF electrolytic capacitor 14-19 L O A D + Co 20 – V IN – V OUT PROGRAMMING PINS For technical support and more information, see inside back cover or visit www.ti.com • C1 = Optional 33µF, 100V electrolytic capacitor • C2 = Optional 1µF, 100V ceramic capacitor • Programming pins, VID1–VID4, are shown configured for Vo =5.0V • For normal operation, pin 3 (Inhibit) must be connected to –Vin. For technical support and more information, see inside back cover or visit www.ti.com Typical Characteristics PT4484—48V 100-W 20-A Programmable Isolated DC/DC Converter Performance Characteristics, Vo =5V (See Note A) Safe Operating Area, Vin =48V (See Note B) Stand Alone, No Heatsink Efficiency vs Output Current 90 100 Efficiency - % VIN 80 48.0V 36.0V 75.0V 70 60 Ambient Temperature (°C) 80 90 Airflow 70 300LFM 200LFM 100LFM Nat conv 60 50 40 30 50 20 0 4 8 12 16 0 20 Iout (A) 4 8 12 16 Iout (A) Ripple vs Output Current 100 80 Ripple - mV VIN 60 75.0V 48.0V 36.0V 40 20 0 0 4 8 12 16 20 Iout (A) Power Dissipation vs Output Current 14 12 Pd - Watts 10 VIN 8 75.0V 36.0V 48.0V 6 4 2 0 0 4 8 12 16 20 Iout (A) Note A: Characteristic data has been developed from actual products tested at 25°C. This data is considered typical data for the Converter. Note B: SOA curves represent the conditions at which internal components are at or below the manufacturer’s maximum operating temperatures For technical support and more information, see inside back cover or visit www.ti.com 20 Application Notes PT4484, PT4498 Increasing the Output Current of the PT4484 with the PT4498 Compatible Current Booster Notes: 1. Refer to the PT4484 specification table for the performance of the regulator/booster combination. The PT4498 is a 20-A “Current Booster” module designed specifically for the PT4484 programmable DC/DC converter. The booster is controlled directly by the regulator, and effectively adds an additional output stage that operates in parallel. This allows the system to run sychronously, providing a low noise solution. Up to two booster modules can be connected to a PT4484 converter. Each booster module increases the available output current by 20A. A combination of one PT4484 converter and two PT4498 booster modules can supply up to 60A of output current; enough to supply a large multiprocessor system. Figure 1-1 shows the connection schematic for the regulator and current booster combination. 2. The pin-out of the current booster modules include a number pins identified, “Do not connect” (see Table 1-1). These pins are not connected internally to the module but must be soldered to a pad to preserve the unit’s mechanical integrity. 3. A minimum of 150µF of output capacitance is required across the output of each PT4498 booster for proper operation. A value greater than 150µF will further reduce transients due to large and/or fast load steps. 4. The converter and all boosters must be located on the same printed circuit board. A similar footprint and trace layout for each module will also facilitate current sharing. Table 1-1; Booster Pin-Out Information A current booster is not a stand-alone product, and can only operate with a regulator. It is housed in the same package as its compatible regulator, and shares the same mechanical outline. Except for an increase in output current, the overall performance of a converter/booster combination is identical to that of a stand-alone converter. Pin Function Pin Function Pin Function 1 +Vin 10 +Vout 19 –Vout 2 –V in 11 +Vout 20 (–)Vsense 3 4 Do not connect Vr 12 +Vout 13 +Vout 21 Do not connect 22 Do not connect 5 Va 14 –Vout 23 Do not connect 6 Do not connect 15 –Vout 24 Do not connect 7 8 Do not connect +V out 16 –Vout 17 –Vout 25 Do not connect 26 DRV 9 +V out 18 –Vout Figure 1-1; Current Booster Application Schematic PROGRAMMING PINS VID1 VID2 VID3 VID4 REMOTE SENSE (+) 25 +VIN Inhibit 1 CIN 33µF Optional + 24 23 7 22 PT4484 2 3 4 5 26 20 +VOUT 8 - 13 14-19 COUT 150µF Optional + LOAD -VOUT –VIN REMOTE SENSE (-) 4 5 26 1 CIN 33µF Optional + 20 PT4498 2 8 - 13 COUT 150µF Required 3 14 - 19 + For technical support and more information, see inside back cover or visit www.ti.com Application Notes PT4470, PT4480 Series Operating Features of the PT4470 and PT4480 Series of Isolated DC/DC Converters Under-Voltage Lockout An Under-Voltage Lock-Out (UVLO) inhibits the operation of the converter until the input voltage is above the UVLO threshold (see the applicable data sheet specification). Below this voltage, the module’s output is held off, irrespective of the state of the Inhibit control (pin 3). If the Inhibit control is connected to –Vin (pin 2), the module will automatically power up when the input voltage rises above the UVLO threshold. The UVLO allows the module to produce a clean transition during both power-up and power-down, even when the input voltage is rising or falling slowly. It also reduces the high start-up current during normal power-up of the converter, and minimizes the current drain from the input source during low-input voltage conditions. The UVLO threshold includes about 2V of hysteresis. Once operational, the converter will conform to its operating specifications when the minimum specified input voltage is reached. Over-Current Protection To protect against load faults, the PT4470/80 series of DC/DC converters incorporate an output current limit. Once the load current drawn from the module reaches the current limit threshold, any attempt by the load to draw additional current will result in a significant drop in the module’s regulated output voltage. The current limit circuitry incorporates a limited amount of foldback. This has the effect of slightly reducing the output current from the module when supplying an absolute short circuit. Upon removal of the load fault, the output voltage from the converter will automatically recover to its programmed regulation voltage. Output Over-Voltage Protection The PT4470/80 series of DC/DC converters incorporate circuitry that continually senses the output for an overvoltage (OV) condition. The OV threshold automatically tracks the VID output voltage program setting to a level 25% higher than that programmed at the control pins, VID0 through VID4. If the converter output voltage exceeds the OV threshold, the converter is immediately shut down and remains in a latched-off state. To resume normal operation the converter must be actively reset. This is accomplished by either cycling the status of the Inhibit control (pin 3) from “On” to “Off” and then back “On” again, or by momentarily removing the input power to the converter. For failsafe operation and redundancy, the OV protection uses circuitry that is independent of the converter’s internal feedback loop. For technical support and more information, see inside back cover or visit www.ti.com Over-Temperature Protection Over-temperature protection is provided by an internal temperature sensor, which closely monitors the temperature of the converter’s metal case. If the case temperature exceeds the specified limit (see applicable data sheet), the converter will shut down. The converter will then automatically restart when the sensed temperature drops by about 10°C. When operated outside its recommended thermal derating envelope (see data sheet SOA curves), the converter will typcially cycle on and off at intervals from a few seconds to one or two minutes. This is to ensure that the internal components are not permanently damaged from excessive thermal stress. Primary-Secondary Isolation Electrical isolation is provided between the input terminals (primary) and the output terminals (secondary). All converters are production tested to a primary-secondary withstand voltage of 1500VDC. This specification complies with UL60950 and EN60950 and the requirements for operational isolation. Operational isolation allows these converters to be configured for either a positive or negative input voltage source. The data sheet ‘Pin-Out Information’ uses shading to indicate which pins are associated with the primary. They include pins 1 through 5, inclusive. Fuse Recommendations If desired, an input fuse may be added to protect against the application of a reverse input voltage. Thermal Considerations Airflow may be necessary to ensure that the module can supply the desired load current in environments with elevated ambient temperatures. The required airflow rate may be determined from the Safe Operating Area (SOA) thermal derating chart (see converter specifications). The recommended direction for airflow is into the longest side of the module’s metal case. See Figure 1. Figure 1 Recommended direction for airflow is into (perpendicular to) the longest side. Application Notes PT4470, PT4480 Series Using the Inhibit Function on the PT4470 & PT4480 Series of Isolated DC/DC Converters The PT4470/44480 series of DC/DC converters incorporate an On/Off Inhibit function. This function may be used in applications that demand battery conservation, power-up/shutdown sequencing, and/or to coordinate power-up for active in-rush current control. The On/Off feature is provided by the Inhibit control, pin 3. The Inhibit pin of the PT4470/4480 series of converters is an active low enable. The pin must be either connected, or actively pulled low, to –Vin (pin 2) to enable the converter output (see standard application schematic). When pins 2 & 3 are connected, the converter provides a regulated output whenever a valid source voltage3 is applied between +Vin (pin 1), and –Vin (pin 2). If pin 3 is disconnected, or allowed to become high impedance, the regulator output will be disabled. 5 Table 2-1 provides details of the interface requirements for the Inhibit pin. Figure 2-1 shows how a discrete MOSFET (Q1) 4, may be referenced to –Vin and used to control the input. Table 2-1 Inhibit Control Requirements Parameter Min Max Enable (VIH) Disable (VIL) –0.5V 2.5V 0.8V (Open Circuit) Notes: 1. The Inhibit control uses –Vin (pin 2), on the primary side of the converter, as its ground reference. All voltages specified are with respect to –Vin. 6. Keep the on/off transition to less than 1ms. This prevents erratic operation of the ISR, whereby the output voltage may drift un-regulated between 0V and the rated output during power-up. Figure 2-1 +V IN 1 + 2 +V in – V in C1 1 =Enable 7 +V sns +V out 8 - 1 3 Inhibit 3 PT4472 VID0 - VID4 21 22 23 24 25 +2.5V -Vout 1 4 - 1 9 -Vsns 20 0V Q1 BSS138 PROGRAMMING PINS –V IN Turn-On Time: With input power applied, the converter typically produces a fully regulated output voltage within 25ms after applying a low-voltage signal to the Inhibit control pin. The actual turn-on time will vary with the input voltage, output load, and the total amount of capacitance connected to the output. Using the circuit of Figure 2-1, Figure 2-2 shows the typical output voltage and input current waveforms of a PT4472 after Q 1 is turned on. The turn on of Q1 correlates to the fall in Vinh. The output voltage was set to 2.5V. The waveform was measured with a 48-Vdc input voltage, and 15-A load current. Figure 2-2 2. The internal circuitry is simple pull-up resistor. The open-circuit voltage may be as high as 6.5Vdc. 3. These converters incorporate an “Under-Voltage Lockout” (UVLO) function. This function automatically disables the converter output until there is sufficient input voltage to produce a regulated output. Table 2 gives the applicable UVLO thresholds. Table 2-2 UVLO Thresholds 1 Series UVLO Threshold PT4470 PT4480 17.0V Typical 34.5V Typical Vout (1V/Div) Iin (2A/Div) Vin Range 18 – 36V 36 – 75V 4. The Inhibit input must be controlled with an opencollector (or open-drain) discrete transistor or MOSFET. Do not use a pull-up resistor. Vinh (5V/Div) HORIZ SCALE: 5ms/Div 5. When the converter output is disabled, the current drawn from the input supply is typically reduced to 4mA (10mA maximum). 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