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ADM1070 Datenblatt(PDF) 9 Page - Analog Devices |
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ADM1070 Datenblatt(HTML) 9 Page - Analog Devices |
9 / 16 page REV. 0 ADM1070 –9– FUNCTIONAL DESCRIPTION HOT CIRCUIT INSERTION Inserting circuit boards into a live –48 V backplane can cause large transient currents to be drawn as the board capacitance charges up. These transient currents can cause glitches on the system power supply and can permanently damage components on the board. The ADM1070 is designed to control the manner in which a board’s supply voltage is applied so that harmful transient currents do not occur and the board can be safely inserted or removed from a live backplane. Undervoltage, overvoltage, and overcurrent pro- tection are other features of the part. The ADM1070 ensures that the input voltage is stable and within tolerance before being applied to the dc-to-dc converter, which generates the low voltage levels required to power the on-board logic. One such converter is the Artesyn EXQ50. Go to www.artesyn.com for more information. ARTESYN EXQ50 CLOAD ADM1070 LIVE BACKPLANE 0V –48V RSENSE PLUG-IN BOARD R1 R2 VIN+ VIN– VOUT+ VOUT– TRIM FET Figure 1. Topology INITIAL STARTUP The ADM1070 hot swap controller normally resides on a remov- able circuit board and controls the manner in which power is applied to the board upon connection. This is achieved using a FET, Q1, in the power path. By controlling the gate voltage of the FET, the surge of current to charge load capacitance can be limited to a safe value when the board makes connection. Note that the ADM1070 can also reside on the backplane itself, and perform the same function from there. TMER ADM1070 R1 R2 UV/OV GATE SENSE VEE Q1 RSENSE CLOAD VOUT RDROP 16k VIN 0V –48V LIVE BACKPLANE Figure 2. Circuit Board Connection Figure 2 shows how a plug-in module containing the ADM1070 makes connection to the backplane supply. When the board is inserted, the –48 V and 0 V lines connect. This powers up the device with the voltage on VIN exceeding VLKO. When the voltage at the UV/OV Pin exceeds undervoltage rising threshold (VUVR) of 0.91 V, it is now inside the operating volt- age window. It must stay inside this window for the duration of the power-on reset delay time, tPOR, which is dependent on the value of CT. When the device detects that the supply voltage is valid, it ramps up the gate voltage until the FET turns on and the load current increases. The ADM1070 monitors the level of the current flowing through the FET by sensing the voltage across the external sense resistor, RSENSE. When the sense voltage reaches 100 mV, the GATE Pin is actively controlled, limiting the load current. In this way, the maximum current permitted to flow through the load is set by the choice of RSENSE. If a change in the level of the supply voltage causes UV/OV to fall below the undervoltage falling threshold of VUVF, or rise above the overvoltage rising threshold of VOVR, then the gate drive will be disabled. BOARD REMOVAL If the board is removed from a card cage, the voltage at the UV/OV pin falls to zero (i.e., outside operating range) and the gate drive is deasserted, turning off the FET. CONTROLLING THE CURRENT The ADM1070 features a current limiting function that protects against short circuits or excessive supply currents. The flow of current through the load is monitored by measuring the voltage across the sense resistor, which is connected between the SENSE and VEE Pins. There are three different types of protection offered: 1. If the voltage across the sense resistor exceeds the circuit breaker limit voltage of 88 mV (rising) for the current limit on time (tLIMITON), then a current fault has occurred and the PWM cycle begins. The FET current is linearly controlled at a maximum of 100 mV/RSENSE (via the gate drive) during tLIMITON (see next section). The gate is then disabled for the duration tOFF. This PWM ratio, which will always be 3%, is given by tON/tOFF. A unique feature of the ADM1070 is the limited consecutive retry function. An internal fault counter keeps track of the number of successive PWM cycles that occur. The fault counter is incremented after every fault is detected. If the ADM1070 detects seven consecutive current faults, it is appar- ent that the fault is not a temporary one and the device latches itself off. The fault counter is cleared if a new tON timeout does not occur within 2 tOFF of the previous tLIMITON timeout. |
Ähnliche Teilenummer - ADM1070 |
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Ähnliche Beschreibung - ADM1070 |
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