Datasheet LTC3543 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | 600mA Synchronous Step Down Buck Regulator with PLL, Soft-Start and Spread Spectrum |
| Pages / Page | 20 / 10 — OPERATION. Slope Compensation and Inductor Peak Current. Low Supply … |
| File Format / Size | PDF / 342 Kb |
| Document Language | English |
OPERATION. Slope Compensation and Inductor Peak Current. Low Supply Operation
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LTC3543
OPERATION
An important detail to remember is that at low input supply
Slope Compensation and Inductor Peak Current
voltages, the RDS(ON) of the P-channel switch increases Slope compensation provides stability in constant- (see the Typical Performance Characteristics section). frequency architectures by preventing subharmon- Therefore, the user should calculate the power dissipation ic oscillations at high duty cycles. It is accomplished when the LTC3543 is used at 100% duty cycle with low internally by adding a compensating ramp to the inductor input voltage (see Thermal Considerations in the Applica- current signal at duty cycles in excess of 40%. Normally, tions Information section). this results in a reduction of maximum inductor peak current for duty cycles >40%; however, the LTC3543
Low Supply Operation
uses a patent pending scheme that counteracts The LTC3543 will operate with input supply voltages as this compensating ramp, allowing the maximum induc- low as 2.5V, but the maximum allowable output current tor peak current to remain unaffected throughout all is reduced at this low voltage. Figure 2 shows the reduc- duty cycles. tion in the maximum output current as a function of input voltage for various output voltages. 1500 1400 1300 1200 VOUT = 1.2V 1100 1000 900 VOUT = 1.5V 800 700 MAXIMUM OUTPUT CURRENT (mA) 600 500 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) 3543 F02
Figure 2. Maximum Output Current vs Input Voltage (VIN)
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OPERATION
An important detail to remember is that at low input supply
Slope Compensation and Inductor Peak Current
voltages, the RDS(ON) of the P-channel switch increases Slope compensation provides stability in constant- (see the Typical Performance Characteristics section). frequency architectures by preventing subharmon- Therefore, the user should calculate the power dissipation ic oscillations at high duty cycles. It is accomplished when the LTC3543 is used at 100% duty cycle with low internally by adding a compensating ramp to the inductor input voltage (see Thermal Considerations in the Applica- current signal at duty cycles in excess of 40%. Normally, tions Information section). this results in a reduction of maximum inductor peak current for duty cycles >40%; however, the LTC3543
Low Supply Operation
uses a patent pending scheme that counteracts The LTC3543 will operate with input supply voltages as this compensating ramp, allowing the maximum induc- low as 2.5V, but the maximum allowable output current tor peak current to remain unaffected throughout all is reduced at this low voltage. Figure 2 shows the reduc- duty cycles. tion in the maximum output current as a function of input voltage for various output voltages. 1500 1400 1300 1200 VOUT = 1.2V 1100 1000 900 VOUT = 1.5V 800 700 MAXIMUM OUTPUT CURRENT (mA) 600 500 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) 3543 F02
Figure 2. Maximum Output Current vs Input Voltage (VIN)
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