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FAN2106 Folha de dados(PDF) 11 Page - Fairchild Semiconductor |
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FAN2106 Folha de dados(HTML) 11 Page - Fairchild Semiconductor |
11 / 15 page © 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN2106 • Rev. 1.1.0 11 MOSFET is fully enhanced. The fault latch is set immediately upon detection. The OV and high-side short fault protections are active all the time, including during soft-start. Over-Temperature Protection (OTP) The chip incorporates an over-temperature protection circuit that sets the fault latch when a die temperature of about 150°C is reached. The IC restarts when the die temperature falls below 125°C. Auto-Restart After a fault, EN pin is discharged by a 1µA current sink to a 1.1V threshold before the internal 800K Ω pull-up is restored. A new soft-start cycle begins when EN charges above 1.35V. Depending on the external circuit, the FAN2106 can be configured to remain latched-off or to automatically restart after a fault. Table 1. Fault / Restart Configurations EN Pin Controller / Restart State Pull to GND OFF (Disabled) Pull-up to VCC with 100K No Restart – Latched OFF (After VCC Comes Up) Open Immediate Restart After Fault Cap. to GND New Soft-Start Cycle After: tDELAY (ms)=3.9 • C(nf) When EN is left open, restart is immediate. If auto-restart is not desired, tie the EN pin to the VCC pin or pull it HIGH after VCC comes up with a logic gate to keep the 1µA current sink from discharging EN to 1.1V. Figure 23 shows one method to pull up EN to VCC for a latch configuration. 14 FAN2106 15 100K EN VCC 3.3n Figure 23. Enable Control with Latch Option Power-Good (PGOOD) Signal PGOOD is an open-drain output that asserts LOW when VOUT is out of regulation, as measured at the FB pin. Thresholds are specified in the Electrical Specifications section. PGOOD does not assert HIGH until the fault latch is enabled (T1.0) (see Figure 22). Application Information Bias Supply The FAN2106 requires a 5V supply rail to bias the IC and provide gate-drive energy. Connect a ≥ 1.0µf X5R or X7R decoupling capacitor between VCC and PGND. Since VCC is used to drive the internal MOSFET gates, supply current is frequency and voltage dependent. Approximate VCC current (ICC) can be calculated using: )] 128 f ( ) 013 . 0 227 5 V [( 58 . 4 I CC ) mA ( CC − • + − + = (1) where frequency (f) is expressed in KHz. Setting the Output Voltage The output voltage of the regulator can be set from 0.8V to 80% of VIN by an external resistor divider (R1 and RBIAS in Figure 1). For output voltages > 5V, output current rating may need to be de-rated depending upon the ambient temperature, power dissipated in the package and the PCB layout. The external resistor divider is calculated using: nA 650 1 R V 8 . 0 V R V 8 . 0 OUT BIAS + − = (2) Connect RBIAS between FB and AGND. If R1 is open (see Figure 1), the output voltage is not regulated eventually causing a latched fault after the soft start is complete (T1.0) If the parallel combination of R1 and RBIAS is ≤ 1KΩ, the internal SS ramp is not released and the regulator does not start. Setting the Switching Frequency Switching frequency is determined by an external resistor, RT, connected between the R(T) pin and AGND: 65 135 ) f / 10 ( R 6 ) K ( T − = Ω (3) where RT is in KΩ and frequency (f) is in KHz. The regulator cannot start if RT is left open. Calculating the Inductor Value Typically the inductor value is chosen based on ripple current ( ΔIL), which is chosen between 10 to 35% of the maximum DC load. Regulator designs that require fast transient response use a higher ripple-current setting, while regulator designs that require higher efficiency keep ripple current on the low side and operate at a lower switching frequency. The inductor value is calculated by the following formula: |
Nº de peça semelhante - FAN2106 |
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Descrição semelhante - FAN2106 |
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