Combining reverse operation and burst mode in ISL81601

Question

Hello. 
 Is it possible for ISL81601 to work in burst mode for light loads on Output, but also to allow reverse mode when voltage drop at Input occure? 
 From what i understand: 
 - adding resistor from LG1 to PGND enables reverse mode, but disables burst mode 
 - removing resistor from LG1 to PGND disables reverse mode, but enables burst mode 
 
 I'm trying to use ISL81601 to build supercapacitor DC-UPS. Capacitors are on the output, powered system and power supply at the input. I would like ISL81601 to work in burst mode while the input power source is online and the capacitors are fully-charged and to switch to reverse mode in case of voltage drop at the input. 
 
 Best Regards 
 Dominik Bejma

AK_Renesas · Answer

Hi Domink, 
 "The ISL81601 can support both burst mode for light load efficiency (that is when input power source is online, and the capacitors are fully charged) and reverse power mode for back feeding power from the output to the input (in case of voltage drop at the input). 
 Let me clarify more: 
 1. When the converter operates in forced PWM mode this allows the reverse flow of coil current, helps in maintaining active control over the power flow, making it possible for the ISL81601 to effectively manage reverse current flow and support input voltage regulation during drops. This capability is crucial for applications like UPS systems, where maintaining power to the input is essential during voltage sags or power interruptions. 
 2. The diode emulation mode (DE mode) is used for burst-mode operation, where the regulator switches off during the duty cycle when the inductor current crosses zero. In this mode, the driver automatically detects this zero-crossing point and turns off the low-side FET at that moment, effectively emulating diode action. This approach allows the body diode to conduct and reduces additional power loss, even while the inductor current remains positive. 
 
 In order to achieve the above-mentioned points, kindly go through the steps below: 
 3. The pin number 2 (QFN) or pin number 9 (HTTSOP) is the input voltage feedback pin for reverse direction operation. Use a resistor divider to feed the input voltage back to this pin. When the input voltage drops to the pin voltage below 0.8V, the internal control loop reduces the duty cycle to sink in current from output to input to keep the pin voltage regulated at 0.8V. Keep the pin voltage below 0.3V to disable the reverse direction operation. 
 
 4. While the LG1 pin (pin number 22 on QFN or pin number 32 on HTTSOP) sets the PWM mode using a resistor connected between the pin and ground during the initiation stage before soft-start, if the pin voltage is less than 0.3V, the converter is set to forced PWM mode; otherwise, if the voltage is higher than 0.3V, the ISL81601 is set to DE mode for burst mode operation to improve light load efficiency. 
 Adding resistor from LG1 to PGND won't affect burst mode and reverse mode at a time. Kindly give me an update if you have any other query. 
 
 Regards, 
 Avinash Kumar

Combining reverse operation and burst mode in ISL81601

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