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4

AN1288.1

October 30, 2008

Start-up

The ISL8105B starts up when V

BIAS

 rises above POR 

threshold and the COMP/EN rises above V

DISABLE

 level. The 

entire start-up time sequence from POR typically takes up to 
23.8ms; up to 10.2ms for the delay and the Overcurrent 
Protection (OCP) sample and hold operation. The initial delay 
is added to allow the bias voltage to rise/exceed 6.5V, so that 
the internal bias regulator can turn on cleanly. When the OCP 
sampling and hold operations are done, the soft-start function 
internally ramps the reference on the non-inverting terminal of 
the error amp from 0V to 0.6V in 13.6ms (typ).

Figure 3 shows the start-up profile of the ISL8105BEVAL1Z, 
ISL8105BEVAL2Z in relation to the start-up of the 12V input 
supply and the bias supply.

Soft-Start with Pre-Biased Output

If the output is pre-biased to a voltage less than the expected 
value, the ISL8105BEVAL1Z, ISL8105BEVAL2Z will detect 
that condition. Neither MOSFETs will turn on until the 
soft-start ramp voltage exceeds the FB voltage; V

OUT

 starts 

seamlessly ramping from there.

Output Ripple

Figure 5 shows the ripple voltage on the output of the 
regulator.

Verifying Loop Gain

Figure 6 shows the measurement of loop gain of the 
converter with feedback network design in the previous 
sections.

FIGURE 3. SOFT-START

V

IN

 = 12V, V

OUT

 = 1.8V, I

OUT

 = 15A

COMP

VOUT

IL

LX

FIGURE 4. SOFT-START WITH PRE-BIASED OUTPUT

V

IN

 = 12V, V

OUT

 = 1.8V, I

OUT

 = 1A

Vout

COMP

Lx

FIGURE 5. OUTPUT RIPPLE (20MHz BW)

FIGURE 6. LOOP GAIN MEASUREMENT AT +25°C

Application Note 1288

Содержание ISL8105BEVAL1Z

Страница 1: ...ents ESR and capacitor charge are major contributions to the output voltage ripple Assuming that the total output capacitance is sufficient then the output voltage ripple is dominated by the ESR which...

Страница 2: ...n loss in the high side MOSFET is calculated using Equation 11 The switching loss in the high side MOSFET can be approximated using Equation 12 where ttr is the combined ON and OFF MOSFET transition t...

Страница 3: ...rks for Single Phase Voltage Mode Buck Regulators Evaluation Board Performance Figure 2 shows a photograph of the ISL8105BEVAL1Z Power and Load Connections Terminals J1 and J2 are connected to the inp...

Страница 4: ...the ISL8105BEVAL1Z ISL8105BEVAL2Z in relation to the start up of the 12V input supply and the bias supply Soft Start with Pre Biased Output If the output is pre biased to a voltage less than the expec...

Страница 5: ...FN6306 5V or 12V Single Phase Synchronous Buck Converter PWM Controller with Integrated MOSFET Gate Drivers Intersil Corporation 2 Tech Brief TB417 Designing Stable Compensation Networks for Single Ph...

Страница 6: ...7 DNP C17 DNP C11 330uF C11 330uF C8 680pF C8 680pF J2 VBIAS J2 VBIAS Q6 DNP Q6 DNP C18 470uF C18 470uF U1 ISL8105B U1 ISL8105B TGATE 2 BGATE BSOC 4 VBIAS 5 FB 6 COMP EN 7 GND 3 BOOT 1 LX 8 C7 DNP C7...

Страница 7: ...num Capacitor 330 F 35V RAD 10x20 Sanyo 14 C18 C19 C20 C21 4 2R5TPF470ML Organic Alumium Capacitor 470 F 2 5V 20 ROHS Case D3L Sanyo 15 C6 C7 C14 C15 C16 C17 C22 C23 C24 C25 C26 DNP RESISTORS 16 R1 1...

Страница 8: ...FIGURE 12 ISL8105BEVAL1Z TOP LAYER SILKSCREEN FIGURE 13 ISL8105BEVAL1Z TOP LAYER COMPONENT SIDE FIGURE 14 ISL8105BEVAL1Z LAYER 2 FIGURE 15 ISL8105BEVAL1Z LAYER 3 FIGURE 16 ISL8105BEVAL1Z BOTTOM LAYER...

Страница 9: ...19 470uF R5 1 74k R5 1 74k Q1 Q1 4 1 2 3 5 R8 DNP R8 DNP TP9 TP9 TP8 TP8 Q6 DNP Q6 DNP TP10 TP10 Q3 Q3 4 1 2 3 5 C20 470uF C20 470uF SW1 SW1 1 2 4 3 Q4 DNP Q4 DNP L1 1uH L1 1uH 2 1 C1 10nF C1 10nF R7...

Страница 10: ...2 C13 3 35ME330AX Aluminum Capacitor 330 F 35V RAD 10x20 Sanyo 14 C18 C19 C20 C21 4 2R5TPF470ML Organic Alumium Capacitor 470 F 2 5V 20 ROHS Case D3L Sanyo 15 C6 C7 C14 C15 C16 C17 C22 C23 C24 C25 C26...

Страница 11: ...ore proceeding For information regarding Intersil Corporation and its products see www intersil com AN1288 1 October 30 2008 Application Note 1288 ISL8105BEVAL2Z Printed Circuit Board Layers FIGURE 18...

Страница 12: ...Mouser Electronics Authorized Distributor Click to View Pricing Inventory Delivery Lifecycle Information Intersil ISL8105BEVAL1Z...

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