Datasheet LTC1265, LTC1265-3.3, LTC1265-5 (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | 1.2A, High Efficiency Step-Down DC/DC Converter |
| Páginas / Página | 16 / 9 — APPLICATIO S I FOR ATIO. Absolute Maximum Ratings and Latchup Prevention. … |
| Formato / tamaño de archivo | PDF / 244 Kb |
| Idioma del documento | Inglés |
APPLICATIO S I FOR ATIO. Absolute Maximum Ratings and Latchup Prevention. Figure 3. Low-Battery Comparator
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LTC1265/LTC1265-3.3/LTC1265-5
U U W U APPLICATIO S I FOR ATIO
The output, Pin 3, is an N-channel open drain that goes low
Absolute Maximum Ratings and Latchup Prevention
when the battery voltage is below the threshold set by R3 The absolute maximum ratings specify that SW (Pin 14) and R4. In shutdown, the comparator is disabled and Pin can never exceed V 3 is in a high impedance state. IN (Pins 1, 2, 13) by more than 0.3V. Normally this situation should never occur. It could, however, if the output is held up while the VIN supply is VIN pulled down. A condition where this could potentially R4 occur is when a battery is supplying power to an LTC1265 LTC1265 4 3 regulator and also to one or more loads in parallel with the – the regulator’s VIN. If the battery is disconnected while the LTC1265 regulator is supplying a light load and one of the + R3 parallel circuits has a heavy load, the input capacitor of the LTC1265 regulator could be pulled down faster than the 1.25V REFERENCE output capacitor, causing the absolute maximum ratings LTC1265 F03 to be exceeded. The result is often a latchup which can be destructive if VIN is reapplied quickly. Battery disconnect is possible as a result of mechanical stress, bad battery
Figure 3. Low-Battery Comparator
contacts or use of a lithium-ion battery with a built-in internal disconnect. The user needs to assess his/her
LTC1265 ADJUSTABLE APPLICATIONS
application to determine whether this situation could The LTC1265 develops a 1.25V reference voltage between occur. If so, additional protection is necessary. the feedback (Pin 9) terminal and signal ground (see Prevention against latchup can be accomplished by Figure 4). By selecting resistor R1, a constant current is simply connecting a Schottky diode across the SW and caused to flow through R1 and R2 to set overall output VIN pins as shown in Figure 5. The diode will normally be voltage. The regulated output voltage is determined by: reverse biased unless VIN is pulled below VOUT at which time the diode will clamp the (VOUT – VIN) potential to less than the 0.6V required for latchup. Note that a low leakage V ) OUT = 1.25 1 + R2 R1 Schottky should be used to minimize the effect on no- load supply current. Schottky diodes such as MBR0530, For most applications a 30k resistor is suggested for R1. BAS85 and BAT84 work well. Another more serious To prevent stray pickup, a 100pF capacitor is suggested effect of the protection diode leakage is that at no load across R1 located close to the LTC1265. with nothing to provide a sink for this leakage current, the VOUT LATCHUP PROTECTION R2 SCHOTTKY 9 LTC1265 VFB SGND 100pF PWR R1 SW V V OUT 11 IN + LTC1265 LTC1265 F04 1265 F05
Figure 4. LTC1265 Adjustable Configuration Figure 5. Preventing Absolute Maximum Ratings from Being Exceeded
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U U W U APPLICATIO S I FOR ATIO
The output, Pin 3, is an N-channel open drain that goes low
Absolute Maximum Ratings and Latchup Prevention
when the battery voltage is below the threshold set by R3 The absolute maximum ratings specify that SW (Pin 14) and R4. In shutdown, the comparator is disabled and Pin can never exceed V 3 is in a high impedance state. IN (Pins 1, 2, 13) by more than 0.3V. Normally this situation should never occur. It could, however, if the output is held up while the VIN supply is VIN pulled down. A condition where this could potentially R4 occur is when a battery is supplying power to an LTC1265 LTC1265 4 3 regulator and also to one or more loads in parallel with the – the regulator’s VIN. If the battery is disconnected while the LTC1265 regulator is supplying a light load and one of the + R3 parallel circuits has a heavy load, the input capacitor of the LTC1265 regulator could be pulled down faster than the 1.25V REFERENCE output capacitor, causing the absolute maximum ratings LTC1265 F03 to be exceeded. The result is often a latchup which can be destructive if VIN is reapplied quickly. Battery disconnect is possible as a result of mechanical stress, bad battery
Figure 3. Low-Battery Comparator
contacts or use of a lithium-ion battery with a built-in internal disconnect. The user needs to assess his/her
LTC1265 ADJUSTABLE APPLICATIONS
application to determine whether this situation could The LTC1265 develops a 1.25V reference voltage between occur. If so, additional protection is necessary. the feedback (Pin 9) terminal and signal ground (see Prevention against latchup can be accomplished by Figure 4). By selecting resistor R1, a constant current is simply connecting a Schottky diode across the SW and caused to flow through R1 and R2 to set overall output VIN pins as shown in Figure 5. The diode will normally be voltage. The regulated output voltage is determined by: reverse biased unless VIN is pulled below VOUT at which time the diode will clamp the (VOUT – VIN) potential to less than the 0.6V required for latchup. Note that a low leakage V ) OUT = 1.25 1 + R2 R1 Schottky should be used to minimize the effect on no- load supply current. Schottky diodes such as MBR0530, For most applications a 30k resistor is suggested for R1. BAS85 and BAT84 work well. Another more serious To prevent stray pickup, a 100pF capacitor is suggested effect of the protection diode leakage is that at no load across R1 located close to the LTC1265. with nothing to provide a sink for this leakage current, the VOUT LATCHUP PROTECTION R2 SCHOTTKY 9 LTC1265 VFB SGND 100pF PWR R1 SW V V OUT 11 IN + LTC1265 LTC1265 F04 1265 F05
Figure 4. LTC1265 Adjustable Configuration Figure 5. Preventing Absolute Maximum Ratings from Being Exceeded
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