Datasheet LT1074, LT1076 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Step-Down Switching Regulator |
| Pages / Page | 16 / 10 — PI DESCRIPTIO S. Figure 7. Adding Hysteresis. Figure 5. Shutdown … |
| File Format / Size | PDF / 189 Kb |
| Document Language | English |
PI DESCRIPTIO S. Figure 7. Adding Hysteresis. Figure 5. Shutdown Circuitry. Undervoltage Lockout. Example:
Model Line for this Datasheet
- LT1074CT#06PBF LT1074CT#30PBF LT1074CT#PBF LT1074CT7#06PBF LT1074CT7#PBF LT1074HVCT#06PBF LT1074HVCT#PBF LT1074HVCT7#06PBF LT1074HVCT7#PBF LT1074HVIT#06PBF LT1074HVIT#30PBF LT1074HVIT#PBF LT1074HVIT7#06PBF LT1074HVIT7#35PBF LT1074HVIT7#PBF LT1074IT#06PBF LT1074IT#PBF LT1074IT7#PBF
- LT1076CQ#PBF LT1076CQ#TRPBF LT1076CR#PBF LT1076CR#TRPBF LT1076CT#06PBF LT1076CT#30PBF LT1076CT#PBF LT1076CT7#PBF LT1076HVCR#PBF LT1076HVCR#TRPBF LT1076HVCT#06PBF LT1076HVCT#PBF LT1076HVCT7#PBF LT1076HVIR#PBF LT1076HVIR#TRPBF LT1076HVIT#06PBF LT1076HVIT#PBF LT1076IQ#PBF LT1076IQ#TRPBF LT1076IR#PBF LT1076IR#TRPBF LT1076IT#06PBF LT1076IT#PBF
Text Version of Document
LT1074/LT1076
U U PI DESCRIPTIO S
VIN Hysteresis in undervoltage lockout may be accomplished by connecting a resistor (R3) from the ILIM pin to the 10 A µ 300 A µ shutdown pin as shown in Figure 7. D1 prevents the shutdown divider from altering current limit. SHUTDOWN – PIN ILIM C1 PIN V 2.3V + R1 IN SHUT Q1 D1* LT1074 6V EXTERNAL R3 CLIM I – LIM C2 R2 OPTIONAL CURRENT 0.3V + LIMIT RESISTOR LT1074•PD09 *1N4148 TO TOTAL REGULATOR SHUTDOWN
Figure 7. Adding Hysteresis
LT1074•PD07
Figure 5. Shutdown Circuitry
⎛ R ⎞ 1 Trip Point = V = . 2 3 V TP 5 1+
Undervoltage Lockout
⎝⎜ R2⎠⎟ Undervoltage lockout point is set by R1 and R2 in Figure 6. If R3 is added, the lower trip point (VIN descending) will be To avoid errors due to the 10µA shutdown pin current, R2 the same. The upper trip point (VUTP) will be: is usually set at 5k, and R1 is found from: ⎛ R1 R1⎞ ⎛ R1⎞ V = V 1 + 0. V 8 V ( −V ) UTP SH TP SH ⎝⎜ R2 R3⎠⎟ − ⎝⎜R3⎠⎟ R1= R2 VSH If R1 and R2 are chosen, R3 is given by: VTP = Desired undervoltage lockout voltage ( . )( ) V V − 0 V 8 R1 SH = Threshold for lockout on the SH R3 = shutdown pin = 2.45V ⎛ R1⎞ V − V 1+ If quiescent supply current is critical, R2 may be increased UTP SH⎝⎜ R2⎠⎟ up to 15kΩ, but the denominator in the formula for R2 should replace VSH with VSH – (10µA)(R2).
Example:
An undervoltage lockout is required such that the output will not start until VIN = 20V, but will continue to operate until VIN drops to 15V. Let R2 = 2.32k. R1 VIN SHUT LT1074 V 15 2 3 . V 5 ( ) R1= 2 3 . k 4 = 12. k 5 ( ) − R2 GND 2 3 . V 5 5k 2.35 ( −0.8 12.5 )( ) R3 = = 3. k 9 LT1074•PD08 ⎛ 12.5⎞
Figure 6. Undervoltage Lockout
20 − 2.35 1+ ⎝⎜ 2.32⎠⎟ sn1074 1074fds 10
U U PI DESCRIPTIO S
VIN Hysteresis in undervoltage lockout may be accomplished by connecting a resistor (R3) from the ILIM pin to the 10 A µ 300 A µ shutdown pin as shown in Figure 7. D1 prevents the shutdown divider from altering current limit. SHUTDOWN – PIN ILIM C1 PIN V 2.3V + R1 IN SHUT Q1 D1* LT1074 6V EXTERNAL R3 CLIM I – LIM C2 R2 OPTIONAL CURRENT 0.3V + LIMIT RESISTOR LT1074•PD09 *1N4148 TO TOTAL REGULATOR SHUTDOWN
Figure 7. Adding Hysteresis
LT1074•PD07
Figure 5. Shutdown Circuitry
⎛ R ⎞ 1 Trip Point = V = . 2 3 V TP 5 1+
Undervoltage Lockout
⎝⎜ R2⎠⎟ Undervoltage lockout point is set by R1 and R2 in Figure 6. If R3 is added, the lower trip point (VIN descending) will be To avoid errors due to the 10µA shutdown pin current, R2 the same. The upper trip point (VUTP) will be: is usually set at 5k, and R1 is found from: ⎛ R1 R1⎞ ⎛ R1⎞ V = V 1 + 0. V 8 V ( −V ) UTP SH TP SH ⎝⎜ R2 R3⎠⎟ − ⎝⎜R3⎠⎟ R1= R2 VSH If R1 and R2 are chosen, R3 is given by: VTP = Desired undervoltage lockout voltage ( . )( ) V V − 0 V 8 R1 SH = Threshold for lockout on the SH R3 = shutdown pin = 2.45V ⎛ R1⎞ V − V 1+ If quiescent supply current is critical, R2 may be increased UTP SH⎝⎜ R2⎠⎟ up to 15kΩ, but the denominator in the formula for R2 should replace VSH with VSH – (10µA)(R2).
Example:
An undervoltage lockout is required such that the output will not start until VIN = 20V, but will continue to operate until VIN drops to 15V. Let R2 = 2.32k. R1 VIN SHUT LT1074 V 15 2 3 . V 5 ( ) R1= 2 3 . k 4 = 12. k 5 ( ) − R2 GND 2 3 . V 5 5k 2.35 ( −0.8 12.5 )( ) R3 = = 3. k 9 LT1074•PD08 ⎛ 12.5⎞
Figure 6. Undervoltage Lockout
20 − 2.35 1+ ⎝⎜ 2.32⎠⎟ sn1074 1074fds 10
