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ISL6120CBZA Datasheet(PDF) 6 Page - Intersil Corporation |
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ISL6120CBZA Datasheet(HTML) 6 Page - Intersil Corporation |
6 / 12 page 6 February 6, 2007 Application Considerations During the soft-start and the time-out delay duration with the IC in its current limit mode, the VGS of the external N-Channel MOSFET is reduced driving the MOSFET switch into a (linear region) high rDS(ON) state. Strike a balance between the CR limit and the timing requirements to avoid periods when the external N-Channel MOSFETs may be damaged or destroyed due to excessive internal power dissipation. Refer to the MOSFET SOA information in the manufacturer’s data sheet. When driving particularly large capacitive loads a longer soft- start time to prevent current regulation upon charging and a short CR time may offer the best application solution relative to reliability and FET MTF. Physical layout of RSENSE resistor is critical to avoid the possibility of false overcurrent occurrences. Ideally, trace routing between the RSENSE resistors and the IC is as direct and as short as possible with zero current in the sense lines (See Figure 1). Using the ISL6116 as a -48V Low Side Hot Swap Power Controller To supply the required VDD, it is necessary to maintain the chip supply 10 to 16V above the -48V bus. This may be accomplished with a suitable regulator between the voltage rail and pin 5 (VDD). By using a regulator, the designer may ignore the bus voltage variations. However, a low-cost alternative is to use a Zener diode (See Figure 2 for typical 5A load control); this option is detailed below. Note that in this configuration the PGOOD feature (pin 7) is not operational as the ISEN pin voltage is always < UV threshold. See Figures 17 to 20 for waveforms relevant to -48V and other high voltage applications. Biasing the ISL6116 Table 3 gives typical component values for biasing the ISL6116 in a ±48V application. The formulas and calculations deriving these values are also shown below. When using the ISL6116 to control -48V, a Zener diode may be used to provide the +12V bias to the chip. If a Zener is used then a current limit resistor should also be used. Several items must be taken into account when choosing values for the current limit resistor (RCL) and Zener Diode (DD1): • The variation of the VBUS (in this case, -48V nominal) • The chip supply current needs for all functional conditions • The power rating of RCL. • The current rating of DD1 Formulas 1. Sizing RCL: RCL = (VBUS,MIN - 12)/ICHIP 2. Power Rating of RCL: PRCL = IC(VBUS,MAX - 12) 3. DD1 Current Rating: IDD1 = (VBUS,MAX - 12)/RCL CORRECT TO ISEN AND CURRENT SENSE RESISTOR INCORRECT FIGURE 1. SENSE RESISTOR PCB LAYOUT RISET TABLE 3. TYPICAL VALUES FOR A -48V HOT SWAP APPLICATION SYMBOL PARAMETER RCL 1.58k Ω, 1W DD1 12V Zener Diode, 50mA Reverse Current VBUS LOAD ISL6116 PWRON NC FIGURE 2. -48V RCL DD1 12V 1.58k Ω 1W 0.01µF 0.047µF 1.47k Ω 0.005 1% 0.001µF 2k Ω 1% ISL6115, ISL6116, ISL6117, ISL6120 |
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