XRP7714ILB-0X18-F Exar Corporation, XRP7714ILB-0X18-F Datasheet - Page 26

• Manufacturer Part Number: XRP7714ILB-0X18-F
• Description: IC CTRLR PWM/LDO STP-DWN 40TQFN
• Manufacturer: Exar Corporation
• Series: -r

Specifications of XRP7714ILB-0X18-F

• Topology: Step-Down (Buck) Synchronous (4), Linear (LDO) (1)
• Function: Any Function
• Number Of Outputs: 5
• Frequency - Switching: 1.5MHz
• Voltage/current - Output 1: Controller
• Voltage/current - Output 2: Controller
• Voltage/current - Output 3: Controller
• W/led Driver: No
• W/supervisor: No
• W/sequencer: Yes
• Voltage - Supply: 4.75 V ~ 25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 1016-1699

Select ESR such that output voltage ripple (Vrip) specification is met. There are two components in
Vrip. First component arises from the charge transferred to and from Cout during each cycle. The
second component of Vrip is due to the inductor ripple current flowing through the output
capacitor’s ESR. It can be calculated for Vrip:
Where:
Irip is the inductor ripple current
fs is the switching frequency
Cout is the output capacitance
Note that a smaller inductor results in a higher Irip, therefore requiring a larger Cout and/or lower
ESR in order to meet Vrip. With the current generation of ultra-low ESR ceramic capacitors it is
common to operate with Irip ≥ 30% of Iout.
When trying to optimize control loop bandwidth, particularly at switching frequencies below
600kHz, an effective ESR in the range of 7 to 20mohm can help significantly. The Digital Power
Studio design tool is used to verify what will work best in your application.
Select the input capacitor for Voltage, Capacitance, ripple current, ESR and ESL. Voltage rating is
nominally selected to be at least twice the input voltage. The RMS value of input capacitor current,
assuming a low inductor ripple current, can be approximated as:
Where:
Iin is the RMS input current
Iout is the DC output current
D is the duty cycle
In general, the total input voltage ripple should be kept below 1.5% of VIN. The input voltage
ripple also has two major components: the voltage drop on the main capacitor
voltage drop due to ESR -
calculated from:
Total input voltage ripple is the sum of the above:
© 2011 Exar Corporation
•
Input Capacitor Selection
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