ISL81601 UPS with low voltage battery/capacitor

Question

Hello! 
 
 I would like build a UPS with only 1 cell of Li-Ion battery (max. 4.2V) or supercapacitor (max. 2.7V). System bus would be 5V. 
 According to the datasheet the minimum voltage on Vin should be minimum 4.5V, so I can't use the Vin side of the dcdc converter for the battery, as discribed in "Design Considerations for a Bidirectional DC/DC Converter" white paper. 
 Is it possible to swap the sides, and use the Vout side of the controller for the battery (min. 0.8V is low enough), and Vin for the system bus? 
 
 Thanks for help in advance. 
 
 Br, 
 Zoltan

AB_RENESAS · Answer

Hi, 
 What's your output /load requirement (v& I). 
 Figure 3 shows the four-switch buck-boost converter operation modes and waveforms controlled by the ISL81601. When Vin is lower than Vout, it runs in boost mode, as shown in Figure 3C. When Vin is higher than Vout, it runs in buck mode, as shown in Figure 3A. When Vin is close to Vout, it runs in buck-boost (one cycle buck followed by one cycle boost) mode as shown in Figure 3B .

Also As per flow of charge & discharge . Vin to Vout is buck converter & Vout to Vin boost converter . If you connect battery at output side you will get boost voltage at input side . & vice versa. 
 Thanks 
 AB

AB_RENESAS · Answer

Hi, 
 Can You share block diagram to understand more . 
 Thanks 
 AB

korg · Answer

Hello, Zoli! I'm glad there is feedback. Now I have created a project 12V source - IS81601 - 4S7P battery from 10V-16V (the battery is hanging on the output of the microcircuit). I am waiting for the components and will include this board. Zoli, tell me the parameters of the circuit. Is the input of the microcircuit hanging on the main 12V line? and the battery is hanging on the output of the microcircuit? What kind of battery do you have? What is the battery voltage range? As I understand the operation of the circuit - (if the main 12V and the load are from the input side of the microcircuit, and the battery is on the output side) - then when the main 12V (at the input) disappears, you need to force the GM2 circuit to change the direction of energy (from the battery towards the main 12V). That is, you need to select a divider for the GM2 circuit slightly below 12V.

ISL81601 UPS with low voltage battery/capacitor

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