Datasheet LTM4624 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | 14VIN, 4A Step-Down DC/DC µModule Regulator |
| Pages / Page | 26 / 9 — APPLICATIONS INFORMATION. Table 1. RFB Resistor Table vs Various Output … |
| File Format / Size | PDF / 350 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Table 1. RFB Resistor Table vs Various Output Voltages. OUT (V). 0.6. 1.0. 1.2. 1.5. 1.8. 2.5. 3.3. 5.0
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LTM4624
APPLICATIONS INFORMATION
The typical LTM4624 application circuit is shown in
Table 1. RFB Resistor Table vs Various Output Voltages
Figure 20. External component selection is primarily
V
determined by the input voltage, the output voltage and
OUT (V) 0.6 1.0 1.2 1.5 1.8 2.5 3.3 5.0
R the maximum load current. Refer to Table 6 for specific FB (kΩ) OPEN 90.9 60.4 40.2 30.1 19.1 13.3 8.25 external capacitor requirements for a particular application.
Input Decoupling Capacitors V
The LTM4624 module should be connected to a low AC
IN to VOUT Step-Down Ratios
impedance DC source. For the regulator, a 10µF input There are restrictions in the maximum VIN and VOUT step- ceramic capacitor is required for RMS ripple current de- down ratios that can be achieved for a given input voltage coupling. Bulk input capacitance is only needed when the due to the minimum off-time and minimum on-time limits input source impedance is compromised by long inductive of the regulator. The minimum off-time limit imposes a leads, traces or not enough source capacitance. The bulk maximum duty cycle which can be calculated as: capacitor can be an aluminum electrolytic capacitor or D polymer capacitor. MAX = 1 – (tOFF(MIN) • fSW) where t Without considering the inductor ripple current, the RMS OFF(MIN) is the minimum off-time, typically 70ns for LTM4624, and f current of the input capacitor can be estimated as: SW (Hz) is the switching frequency. Conversely the minimum on-time limit imposes a minimum IOUT(MAX) duty cycle of the converter which can be calculated as: ICIN(RMS) = • D • (1– D) η% DMIN = tON(MIN) • fSW where η% is the estimated efficiency of the power module. where tON(MIN) is the minimum on-time, typically 40ns for LTM4624. In the rare cases where the minimum duty
Output Decoupling Capacitors
cycle is surpassed, the output voltage will still remain in regulation, but the switching frequency will decrease With an optimized high frequency, high bandwidth design, from its programmed value. Note that additional thermal only a single low ESR output ceramic capacitor is required derating may be applied. See the Thermal Considerations for the LTM4624 to achieve low output ripple voltage and and Output Current Derating section in this data sheet. very good transient response. Additional output filtering may be required by the system designer if further reduction
Output Voltage Programming
of output ripple or dynamic transient spikes is required. Table 6 shows a matrix of different output voltages and The PWM controller has an internal 0.6V reference voltage. output capacitors to minimize the voltage droop and As shown in the Block Diagram, a 60.4k internal feedback overshoot during a 1A and 2A load-step transient. The resistor connects the VOUT and FB pins together. Adding a Linear Technology LTpowerCAD® design tool is available resistor, RFB, from FB pin to SGND programs the output to download online for output ripple, stability and transient voltage: response analysis for further optimization. RFB = 0.6V • 60.4k VOUT – 0.6V 4624fd For more information www.linear.com/LTM4624 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Package Description Package Photo Design Resources Related Parts
APPLICATIONS INFORMATION
The typical LTM4624 application circuit is shown in
Table 1. RFB Resistor Table vs Various Output Voltages
Figure 20. External component selection is primarily
V
determined by the input voltage, the output voltage and
OUT (V) 0.6 1.0 1.2 1.5 1.8 2.5 3.3 5.0
R the maximum load current. Refer to Table 6 for specific FB (kΩ) OPEN 90.9 60.4 40.2 30.1 19.1 13.3 8.25 external capacitor requirements for a particular application.
Input Decoupling Capacitors V
The LTM4624 module should be connected to a low AC
IN to VOUT Step-Down Ratios
impedance DC source. For the regulator, a 10µF input There are restrictions in the maximum VIN and VOUT step- ceramic capacitor is required for RMS ripple current de- down ratios that can be achieved for a given input voltage coupling. Bulk input capacitance is only needed when the due to the minimum off-time and minimum on-time limits input source impedance is compromised by long inductive of the regulator. The minimum off-time limit imposes a leads, traces or not enough source capacitance. The bulk maximum duty cycle which can be calculated as: capacitor can be an aluminum electrolytic capacitor or D polymer capacitor. MAX = 1 – (tOFF(MIN) • fSW) where t Without considering the inductor ripple current, the RMS OFF(MIN) is the minimum off-time, typically 70ns for LTM4624, and f current of the input capacitor can be estimated as: SW (Hz) is the switching frequency. Conversely the minimum on-time limit imposes a minimum IOUT(MAX) duty cycle of the converter which can be calculated as: ICIN(RMS) = • D • (1– D) η% DMIN = tON(MIN) • fSW where η% is the estimated efficiency of the power module. where tON(MIN) is the minimum on-time, typically 40ns for LTM4624. In the rare cases where the minimum duty
Output Decoupling Capacitors
cycle is surpassed, the output voltage will still remain in regulation, but the switching frequency will decrease With an optimized high frequency, high bandwidth design, from its programmed value. Note that additional thermal only a single low ESR output ceramic capacitor is required derating may be applied. See the Thermal Considerations for the LTM4624 to achieve low output ripple voltage and and Output Current Derating section in this data sheet. very good transient response. Additional output filtering may be required by the system designer if further reduction
Output Voltage Programming
of output ripple or dynamic transient spikes is required. Table 6 shows a matrix of different output voltages and The PWM controller has an internal 0.6V reference voltage. output capacitors to minimize the voltage droop and As shown in the Block Diagram, a 60.4k internal feedback overshoot during a 1A and 2A load-step transient. The resistor connects the VOUT and FB pins together. Adding a Linear Technology LTpowerCAD® design tool is available resistor, RFB, from FB pin to SGND programs the output to download online for output ripple, stability and transient voltage: response analysis for further optimization. RFB = 0.6V • 60.4k VOUT – 0.6V 4624fd For more information www.linear.com/LTM4624 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Package Description Package Photo Design Resources Related Parts
