Datasheet LT1611 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Inverting 1.4MHz Switching Regulator in 5-Lead SOT-23 |
| Pages / Page | 12 / 9 — OPERATIO. Start-Up/Soft-Start. Figure 14. RSS and CSS at SHDN Pin Provide … |
| File Format / Size | PDF / 271 Kb |
| Document Language | English |
OPERATIO. Start-Up/Soft-Start. Figure 14. RSS and CSS at SHDN Pin Provide Soft-Start to LT1611 Inverting Converter
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LT1611
U OPERATIO Start-Up/Soft-Start
measured at VIN, is limited to a peak value of 450mA as the time required to reach final value increases to 700µs. In The LT1611, starting from VOUT = 0V, reaches final voltage Figure 16, C in approximately 450µs after SHDN is pulled high, with SS is increased to 0.1µF, resulting in a lower peak input current of 240mA with a V C OUT ramp time of OUT = 22µF, VIN = 5V and VOUT = – 5V. Charging the output 2.1ms. C capacitor at this speed requires an inrush current of over SS can be increased further for an even slower ramp, if desired. Diode D2 serves to quickly discharge C 1A. If a longer start-up time is acceptable, a soft-start SS when V circuit consisting of R SS is driven low to shut down the device. D2 can be SS and CSS, as shown in Figure 14, omitted, resulting in a “soft-stop” slow discharge of the can be used to limit inrush current to a lower value. Figure output capacitor. 15 pictures VOUT and input current, starting into a 33Ω load, with RSS of 33kΩ and CSS of 33nF. Input current, CURRENT C2 L1A L1B PROBE 1µF 22µH 22µH VIN 5V D1 + V C1 IN SW VOUT 22µF –5V R1 R CP SS LT1611 29.4k 33k 1200pF V C3 SS SHDN NFB 22µF GND R2 10k D2 1N4148 CSS 33nF/0.1 C1: AVX TAJB226M010 µF 1611 F14 C2: TAIYO YUDEN LMK212BJ105MG VOUT C3: TAIYO YUDEN JMK325BJ226MM (1210 SIZE) D1: MBR0520 L1: SUMIDA CLS62-220 OR 2× MURATA LQH3C220 (UNCOUPLED)
Figure 14. RSS and CSS at SHDN Pin Provide Soft-Start to LT1611 Inverting Converter
VOUT VOUT 2V/DIV 2V/DIV IIN 200mA/DIV IIN 200mA/DIV VS VS 5V/DIV 5V/DIV LOAD = 150mA 500µs/DIV 1611 F15 LOAD = 150mA 500µs/DIV 1611 F16
Figure 15. RSS = 33k, CSS = 33nF; VOUT Reaches Figure 16. RSS = 33k, CSS = 0.1
µ
F; VOUT Reaches – 5V in 750
µ
s; Input Current Peaks at 450mA – 5V in 2.1ms; Input Current Peaks at 240mA
9
U OPERATIO Start-Up/Soft-Start
measured at VIN, is limited to a peak value of 450mA as the time required to reach final value increases to 700µs. In The LT1611, starting from VOUT = 0V, reaches final voltage Figure 16, C in approximately 450µs after SHDN is pulled high, with SS is increased to 0.1µF, resulting in a lower peak input current of 240mA with a V C OUT ramp time of OUT = 22µF, VIN = 5V and VOUT = – 5V. Charging the output 2.1ms. C capacitor at this speed requires an inrush current of over SS can be increased further for an even slower ramp, if desired. Diode D2 serves to quickly discharge C 1A. If a longer start-up time is acceptable, a soft-start SS when V circuit consisting of R SS is driven low to shut down the device. D2 can be SS and CSS, as shown in Figure 14, omitted, resulting in a “soft-stop” slow discharge of the can be used to limit inrush current to a lower value. Figure output capacitor. 15 pictures VOUT and input current, starting into a 33Ω load, with RSS of 33kΩ and CSS of 33nF. Input current, CURRENT C2 L1A L1B PROBE 1µF 22µH 22µH VIN 5V D1 + V C1 IN SW VOUT 22µF –5V R1 R CP SS LT1611 29.4k 33k 1200pF V C3 SS SHDN NFB 22µF GND R2 10k D2 1N4148 CSS 33nF/0.1 C1: AVX TAJB226M010 µF 1611 F14 C2: TAIYO YUDEN LMK212BJ105MG VOUT C3: TAIYO YUDEN JMK325BJ226MM (1210 SIZE) D1: MBR0520 L1: SUMIDA CLS62-220 OR 2× MURATA LQH3C220 (UNCOUPLED)
Figure 14. RSS and CSS at SHDN Pin Provide Soft-Start to LT1611 Inverting Converter
VOUT VOUT 2V/DIV 2V/DIV IIN 200mA/DIV IIN 200mA/DIV VS VS 5V/DIV 5V/DIV LOAD = 150mA 500µs/DIV 1611 F15 LOAD = 150mA 500µs/DIV 1611 F16
Figure 15. RSS = 33k, CSS = 33nF; VOUT Reaches Figure 16. RSS = 33k, CSS = 0.1
µ
F; VOUT Reaches – 5V in 750
µ
s; Input Current Peaks at 450mA – 5V in 2.1ms; Input Current Peaks at 240mA
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