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TPS61026 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS61026 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 31 page 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 VBAT = 5 V VBAT = 3.6 V VBAT = 2.4 V VBAT = 1.8 V VBAT = 1.2 V VO − Output Voltage − V TPS61020, TPS61024, TPS61025, TPS61026, TPS61027, TPS61028, TPS61029 www.ti.com SLVS451G – SEPTEMBER 2003 – REVISED DECEMBER 2014 Feature Description (continued) 10.3.5 Undervoltage Lockout An undervoltage lockout function prevents device start-up if the supply voltage on VBAT is lower than approximately 0.8 V. When in operation and the battery is being discharged, the device automatically enters the shutdown mode if the voltage on VBAT drops below approximately 0.8 V. This undervoltage lockout function is implemented in order to prevent the malfunctioning of the converter. 10.3.6 Softstart and Short Circuit Protection When the device enables, the internal startup cycle starts with the first step, the precharge phase. During precharge, the rectifying switch is turned on until the output capacitor is charged to a value close to the input voltage. The rectifying switch is current limited during that phase. The current limit increases with the output voltage. This circuit also limits the output current under short circuit conditions at the output. Figure 12 shows the typical precharge current vs output voltage for specific input voltages: Figure 12. Precharge and Short Circuit Current After charging the output capacitor to the input voltage, the device starts switching. If the input voltage is below 1.4 V the device works with a fixed duty cycle of 50% until the output voltage reaches 1.4 V. After that the duty cycle is set depending on the input output voltage ratio. Until the output voltage reaches its nominal value, the boost switch current limit is set to 40% of its nominal value to avoid high peak currents at the battery during startup. As soon as the output voltage is reached, the regulator takes control and the switch current limit is set back to 100%. 10.3.7 Low Battery Detector Circuit—LBI/LBO The low-battery detector circuit is typically used to supervise the battery voltage and to generate an error flag when the battery voltage drops below a user-set threshold voltage. The function is active only when the device is enabled. When the device is disabled, the LBO pin is high-impedance. The switching threshold is 500 mV at LBI. During normal operation, LBO stays at high impedance when the voltage, applied at LBI, is above the threshold. It is active low when the voltage at LBI goes below 500 mV. The battery voltage, at which the detection circuit switches, can be programmed with a resistive divider connected to the LBI pin. The resistive divider scales down the battery voltage to a voltage level of 500 mV, which is then compared to the LBI threshold voltage. The LBI pin has a built-in hysteresis of 10 mV. See the application section for more details about the programming of the LBI threshold. If the low-battery detection circuit is not used, the LBI pin should be connected to GND (or to VBAT) and the LBO pin can be left unconnected. Do not let the LBI pin float. Copyright © 2003–2014, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: TPS61020 TPS61024 TPS61025 TPS61026 TPS61027 TPS61028 TPS61029 |
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