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ADM1060 bảng dữ liệu(PDF) 7 Page - Analog Devices |
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ADM1060 bảng dữ liệu(HTML) 7 Page - Analog Devices |
7 / 45 page ADM1060 INPUTS ADM1060 –7– REV. PrJ 11/02 PRELIMINARY TECHNICAL DATA ADM1060 INPUTS POWERING THE ADM1060 The ADM1060 is powered from the highest voltage input on either the Positive Only supply inputs (VPn) or the High Voltage supply input (VH). The same pins are used for supply fault detection (discussed below) . A VDD Arbi- trator on the device chooses which supply to use. The arbitrator can be considered to be diode OR’ing the posi- tive supplies together (as shown in figure 1). In addition to this, the diodes are supplemented with switches in a synchronous rectifier manner, to minimise voltage loss. This loss can be reduced to ~0.2V, resulting in the ability to power the ADM1060 from a supply as low as 3.0V. Note that the supply on the VBn pins cannot be used to power the device, even if the input on these pins is posi- tive. Also, the minimum supply of 3.0V must appear on one of the VPn pins in order to power up the ADM1060 correctly. A supply of no less than 4.5V can be used on VH. This is because there is no synchronous rectifier circuit on the VH pin, resulting in a voltage drop of ~1.5V across the diode of the VDD Arbitrator. An external cap to GND is required to decouple the on- chip supply from noise. This cap should be connected to the VDDCAP pin, as shown in figure 1. The cap has another use during “brown outs” (momentary loss of power). Under these conditions, where the input supply, VPn, dips transiently below VDD, the synchronous rectifier switch immediately turns off so that it doesn’t pull VDD down. The VDD cap can then act like a reservoir and keep the chip active until the next highest supply takes over the powering of the device. 0.1 F is recommended for this function. Note that in the case where there are 2 or more supplies within 100mV of each other, the supply which takes con- trol of VDD first will keep control (e.g) if VP1 is con- nected to a 3.3V supply, then VDD will power up to approximately 3.1V through VP1. If VP2 is then con- nected to another 3.3V supply, VP1 will still power the device, unless VP2 goes 100mV higher than VP1. VP1 VP2 VP3 VP4 VH Limit current surge to VDDI/ decoupling cap VDDCAP pin Off -chip decoupling capacitor VDDI Figure 1. VDD Arbitrator Operation PROGRAMMABLE SUPPLY FAULT DETECTORS (SFD’S) The ADM1060 has seven programmable Supply Fault Detectors, 1 high voltage detector (2V to 14.4V), 2 bipo- lar detectors (2V to 6V, -2V to -6V) and 4 Positive only voltage detectors (0.6V to 6V). Inputs are applied to these detectors via the VH (High Voltage Supply input) pin, VBn (Bipolar Supply input) pins and VPn (Positive Only input) pins respectively. The SFD’s detect a fault condi- tion on any of these input supplies. A fault is defined as Undervoltage (where the supply drops below a preprogrammed level), Overvoltage (where the supply rises above a preprogrammed level) or Out-of-Window (where the supply deviates outside either the programmed overvoltage OR undervoltage threshold). Only one fault type can be selected at a time. An Undervoltage fault is detected by comparing the input supply to a programmed reference (the undervoltage threshold). If the input voltage drops below the undervoltage threshold the output of the comparator goes high, asserting a fault. The undervoltage threshold is programmed using an 8 bit DAC. On a given range, the UV threshold can be set with a resolution of:- Step Size = Threshold Range/255 An Overvoltage (OV) fault is detected in exactly the same way, using a second comparator and DAC to program the reference. All thresholds are programmed using 8 bit registers, one register each for the 7 UV thresholds and 1 each for the 7 OV thresholds. The UV or OV threshold programmed by the user is given by:- VT= VR x N + VB 255 where:- VT = Desired Threshold Voltage (UV or OV) VR= Threshold Voltage Range N = Decimalized version of 8 bit code VB = Bottom of Threshold Range This results in the code for a given threshold being given by:- N=255 x (VT- VB)/VR Thus, for example, if the user wishes to set a 5V OV threshold on VP1, the code to be programmed in the PS1OVTH register (discussed later) would be given by:- N=255 x (5-2)/4 |
Số phần tương tự - ADM1060 |
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Mô tả tương tự - ADM1060 |
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