Other Parts Discussed in Thread: TPS60400-Q1, TPS60403-Q1,
My customer looks at the datasheet and asked a couple of questions. Would you please give me your comments?
1. Iout vs Cfly
My customer looks at 9.2.2,, but it doesn't say how Iout is related to the Cfly. Would you please tell me how it is?
Note that they'll have Vin =5V and Vout=-5V with Iout=27mA(max) by Cfly=22uF, but they are't sure if they can.
9.2.2 Detailed Design Procedure
For the maximum output current and best performance, three ceramic capacitors of 1 μF (TPS60400-Q1,
TPS60403-Q1) are recommended. For lower currents or higher allowed output voltage ripple, other capacitors
can also be used. TI recommends the output capacitors has a minimum value of 1 μF. With flying capacitors
lower than 1 μF, the maximum output power will decrease.
They look at 8.3.1, but there is no information about Rswitch. Would you please tell me about it?
8.3.1 Charge-Pump Output Resistance
The TPS6040x-Q1 devices are not voltage regulators. The output source resistance of the charge pumps is
approximately 15 Ω at room temperature (with VI = 5 V), and VO approaches –5 V when lightly loaded. VO will
droop toward GND as load current increases as seen in Equation 1.
• RO = output resistance of the converter
• RSWITCH = resistance of a single MOSFET-switch inside the converter
• fOSC = oscillator frequency