Datasheet LT1616 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | 600mA, 1.4MHz Step-Down Switching Regulator in SOT-23 |
| Pages / Page | 16 / 10 — APPLICATIO S I FOR ATIO. BOOST Pin Considerations. Minimum Input Voltage … |
| File Format / Size | PDF / 288 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. BOOST Pin Considerations. Minimum Input Voltage V. OUT = 3.3V. Minimum Input Voltage VOUT = 5V. (5a). (5b)
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LT1616
U U W U APPLICATIO S I FOR ATIO BOOST Pin Considerations
charged. Because the boost capacitor is charged with the Capacitor C3 and diode D2 are used to generate a boost energy stored in the inductor, the circuit will rely on some voltage that is higher than the input voltage. In most cases minimum load current to get the boost circuit running a 0.01µF capacitor and fast switching diode (such as the properly. This minimum load will depend on input and 1N4148 or 1N914) will work well. Figure 5 shows two output voltages, and on the arrangement of the boost ways to arrange the boost circuit. The BOOST pin must be circuit. The minimum load generally goes to zero once the more than 2.5V above the SW pin for best efficiency. For circuit has started. Figure 6 shows a plot of minimum load outputs of 3.3V and above, the standard circuit (Figure 5a) to start and to run as a function of input voltage. In many is best. For outputs between 2.8V and 3.3V, use a 0.033µF cases the discharged output capacitor will present a load capacitor and a small Schottky diode (such as the to the switcher which will allow it to start. The plots show BAT-54). For lower output voltages the boost diode can be the worst-case situation where VIN is ramping very slowly. tied to the input (Figure 5b). The circuit in Figure 5a is more Use a Schottky diode (such as the BAT-54) for the lowest efficient because the BOOST pin current comes from a start-up voltage. lower voltage source. You must also be sure that the
Minimum Input Voltage V
maximum voltage rating of the BOOST pin is not exceeded.
OUT = 3.3V
7 VOUT = 3.3V The minimum operating voltage of an LT1616 application BOOST DIODE DBOOST = BAT54 is limited by the undervoltage lockout (< 3.6V) and by the TIED TO OUTPUT 6 maximum duty cycle as outlined above. For proper start- BOOST DIODE TIED TO INPUT up, the minimum input voltage is also limited by the boost V TO START circuit. If the input voltage is ramped slowly, or the LT1616 5 is turned on with its SHDN pin when the output is already in regulation, then the boost capacitor may not be fully INPUT VOLTAGE (V) 4 D2 V TO RUN 3 1 10 100 500 BOOST C3 LOAD CURRENT (mA) LT1616 1616 F06a VIN VIN SW VOUT
Minimum Input Voltage VOUT = 5V
GND 9 V 1616 F05a OUT = 5V BOOST DIODE DBOOST = BAT54 VBOOST – VSW ≅ VOUT TIED TO OUTPUT MAX VBOOST ≅ VIN + VOUT 8 BOOST DIODE
(5a)
TIED TO INPUT D2 7 V TO START BOOST C3 LT1616 6 VIN VIN SW VOUT INPUT VOLTAGE (V) 5 V TO RUN GND 1616 F05b 4 VBOOST – VSW ≅ VIN 1 10 100 500 MAX VBOOST ≅ 2VIN LOAD CURRENT (mA)
(5b)
1616 F06b
Figure 5. Two Circuits for Generating the Boost Voltage Figure 6. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
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U U W U APPLICATIO S I FOR ATIO BOOST Pin Considerations
charged. Because the boost capacitor is charged with the Capacitor C3 and diode D2 are used to generate a boost energy stored in the inductor, the circuit will rely on some voltage that is higher than the input voltage. In most cases minimum load current to get the boost circuit running a 0.01µF capacitor and fast switching diode (such as the properly. This minimum load will depend on input and 1N4148 or 1N914) will work well. Figure 5 shows two output voltages, and on the arrangement of the boost ways to arrange the boost circuit. The BOOST pin must be circuit. The minimum load generally goes to zero once the more than 2.5V above the SW pin for best efficiency. For circuit has started. Figure 6 shows a plot of minimum load outputs of 3.3V and above, the standard circuit (Figure 5a) to start and to run as a function of input voltage. In many is best. For outputs between 2.8V and 3.3V, use a 0.033µF cases the discharged output capacitor will present a load capacitor and a small Schottky diode (such as the to the switcher which will allow it to start. The plots show BAT-54). For lower output voltages the boost diode can be the worst-case situation where VIN is ramping very slowly. tied to the input (Figure 5b). The circuit in Figure 5a is more Use a Schottky diode (such as the BAT-54) for the lowest efficient because the BOOST pin current comes from a start-up voltage. lower voltage source. You must also be sure that the
Minimum Input Voltage V
maximum voltage rating of the BOOST pin is not exceeded.
OUT = 3.3V
7 VOUT = 3.3V The minimum operating voltage of an LT1616 application BOOST DIODE DBOOST = BAT54 is limited by the undervoltage lockout (< 3.6V) and by the TIED TO OUTPUT 6 maximum duty cycle as outlined above. For proper start- BOOST DIODE TIED TO INPUT up, the minimum input voltage is also limited by the boost V TO START circuit. If the input voltage is ramped slowly, or the LT1616 5 is turned on with its SHDN pin when the output is already in regulation, then the boost capacitor may not be fully INPUT VOLTAGE (V) 4 D2 V TO RUN 3 1 10 100 500 BOOST C3 LOAD CURRENT (mA) LT1616 1616 F06a VIN VIN SW VOUT
Minimum Input Voltage VOUT = 5V
GND 9 V 1616 F05a OUT = 5V BOOST DIODE DBOOST = BAT54 VBOOST – VSW ≅ VOUT TIED TO OUTPUT MAX VBOOST ≅ VIN + VOUT 8 BOOST DIODE
(5a)
TIED TO INPUT D2 7 V TO START BOOST C3 LT1616 6 VIN VIN SW VOUT INPUT VOLTAGE (V) 5 V TO RUN GND 1616 F05b 4 VBOOST – VSW ≅ VIN 1 10 100 500 MAX VBOOST ≅ 2VIN LOAD CURRENT (mA)
(5b)
1616 F06b
Figure 5. Two Circuits for Generating the Boost Voltage Figure 6. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
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