Datasheet LT1611 (Analog Devices) - 10

LT1611
U OPERATIO Output Current COMPONENT SELECTION
The LT1611 will deliver 150mA at – 5V from a 5V ±10%
Inductors
input supply. If a higher voltage supply is available, more output current can be obtained. Figure 17’s schematic Each of the two inductors used with the LT1611 should shows how to get more current. Although the LT1611’s have a saturation current rating (where inductance is maximum voltage allowed at V approximately 70% of zero current inductance) of ap- IN is 10V, the SW pin can handle higher voltage (up to 36V). In Figure 17, the V proximately 0.25A or greater. If the device is used in IN pin of the LT1611 is driven from a 5V supply, while input “charge pump” mode, where there is only one inductor, inductor L then its rating should be 0.5A or greater. DCR of the 1A is driven from a separate 12V supply. Figure 18’s graph shows maximum recommended output cur- inductors should be 0.5Ω or less. A value of 22µH is rent as the voltage on L suitable if using a coupled inductor such as Sumida 1A is varied. Up to 300mA can be delivered when driving L CLS62-220 or Coiltronics CTX20-1. If using two separate 1A from a 12V supply. inductors, increasing the value to 47µH will result in the same ripple current. Inductance can be reduced if operat- ing from a supply voltage below 3V. Table 1 lists several inductors that will work with the LT1611, although this is not an exhaustive list. There are many magnetics vendors whose components are suitable. VL (SEE TEXT) L1A 350 C2 22µH L1B 1µF 22µH 5V 300 D1 VIN SW VOUT 250 –5V SHDN UP TO 300mA 29.4k 1200pF C1 LT1611 200 1µF C3 NFB 22µF GND OUTPUT CURRENT (mA) 10k MAXIMUM RECOMMENDED 150 100 C1, C2: TAIYO YUDEN LMK212BJ105MG 1611 F17 3 4 5 6 7 8 9 10 11 12 C3: TAIYO YUDEN JMK325BJ226MM V D1: MBR0520 L (V) L1A, L1B: SUMIDA CLS62-220 1611 F18
Figure 17. Increase Output Current By Driving L1A from a Higher Voltage Figure 18. Output Current Increases to 300mA When Driving VL from 12V Supply
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