Datasheet LTC3406, LTC3406-1.5, LTC3406-1.8 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT |
| Pages / Page | 16 / 7 — OPERATIO (Refer to Functional Diagram). Short-Circuit Protection. Slope … |
| File Format / Size | PDF / 247 Kb |
| Document Language | English |
OPERATIO (Refer to Functional Diagram). Short-Circuit Protection. Slope Compensation and Inductor Peak Current
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LTC3406 LTC3406-1.5/LTC3406-1.8
U OPERATIO (Refer to Functional Diagram) Short-Circuit Protection
in the maximum output current as a function of input voltage for various output voltages. When the output is shorted to ground, the frequency of the oscillator is reduced to about 210kHz, 1/7 the nominal
Slope Compensation and Inductor Peak Current
frequency. This frequency foldback ensures that the in- ductor current has more time to decay, thereby preventing Slope compensation provides stability in constant fre- runaway. The oscillator’s frequency will progressively quency architectures by preventing subharmonic oscilla- increase to 1.5MHz when V tions at high duty cycles. It is accomplished internally by FB or VOUT rises above 0V. adding a compensating ramp to the inductor current
Dropout Operation
signal at duty cycles in excess of 40%. Normally, this results in a reduction of maximum inductor peak current As the input supply voltage decreases to a value approach- for duty cycles > 40%. However, the LTC3406 uses a ing the output voltage, the duty cycle increases toward the patent-pending scheme that counteracts this compensat- maximum on-time. Further reduction of the supply voltage ing ramp, which allows the maximum inductor peak forces the main switch to remain on for more than one cycle current to remain unaffected throughout all duty cycles. until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor. 1200 An important detail to remember is that at low input supply 1000 voltages, the RDS(ON) of the P-channel switch increases VOUT = 1.8V 800 (see Typical Performance Characteristics). Therefore, the VOUT = 2.5V V user should calculate the power dissipation when the OUT = 1.5V 600 LTC3406 is used at 100% duty cycle with low input voltage (See Thermal Considerations in the Applications Informa- 400 tion section). 200 MAXIMUM OUTPUT CURRENT (mA)
Low Supply Operation
02.5 3.0 3.5 4.0 4.5 5.0 5.5 The LTC3406 will operate with input supply voltages as SUPPLY VOLTAGE (V) 3406 F02 low as 2.5V, but the maximum allowable output current is reduced at this low voltage. Figure 2 shows the reduction
Figure 2. Maximum Output Current vs Input Voltage
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U OPERATIO (Refer to Functional Diagram) Short-Circuit Protection
in the maximum output current as a function of input voltage for various output voltages. When the output is shorted to ground, the frequency of the oscillator is reduced to about 210kHz, 1/7 the nominal
Slope Compensation and Inductor Peak Current
frequency. This frequency foldback ensures that the in- ductor current has more time to decay, thereby preventing Slope compensation provides stability in constant fre- runaway. The oscillator’s frequency will progressively quency architectures by preventing subharmonic oscilla- increase to 1.5MHz when V tions at high duty cycles. It is accomplished internally by FB or VOUT rises above 0V. adding a compensating ramp to the inductor current
Dropout Operation
signal at duty cycles in excess of 40%. Normally, this results in a reduction of maximum inductor peak current As the input supply voltage decreases to a value approach- for duty cycles > 40%. However, the LTC3406 uses a ing the output voltage, the duty cycle increases toward the patent-pending scheme that counteracts this compensat- maximum on-time. Further reduction of the supply voltage ing ramp, which allows the maximum inductor peak forces the main switch to remain on for more than one cycle current to remain unaffected throughout all duty cycles. until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor. 1200 An important detail to remember is that at low input supply 1000 voltages, the RDS(ON) of the P-channel switch increases VOUT = 1.8V 800 (see Typical Performance Characteristics). Therefore, the VOUT = 2.5V V user should calculate the power dissipation when the OUT = 1.5V 600 LTC3406 is used at 100% duty cycle with low input voltage (See Thermal Considerations in the Applications Informa- 400 tion section). 200 MAXIMUM OUTPUT CURRENT (mA)
Low Supply Operation
02.5 3.0 3.5 4.0 4.5 5.0 5.5 The LTC3406 will operate with input supply voltages as SUPPLY VOLTAGE (V) 3406 F02 low as 2.5V, but the maximum allowable output current is reduced at this low voltage. Figure 2 shows the reduction
Figure 2. Maximum Output Current vs Input Voltage
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