Datasheet LT8364 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Low IQ Boost/SEPIC/Inverting Converter with 4A, 60V Switch |
| Pages / Page | 30 / 10 — APPLICATIONS INFORMATION. ACHIEVING ULTRALOW QUIESCENT CURRENT. Figure 2. … |
| File Format / Size | PDF / 2.5 Mb |
| Document Language | English |
APPLICATIONS INFORMATION. ACHIEVING ULTRALOW QUIESCENT CURRENT. Figure 2. Burst Mode Operation
Model Line for this Datasheet
- LT8364EDE#PBF LT8364EDE#PBF LT8364EDE#TRPBF LT8364EDE#TRPBF LT8364EMSE#PBF LT8364EMSE#PBF LT8364EMSE#TRPBF LT8364EMSE#TRPBF LT8364HDE#PBF LT8364HDE#PBF LT8364HDE#TRPBF LT8364HDE#TRPBF LT8364HMSE#PBF LT8364HMSE#PBF LT8364HMSE#TRPBF LT8364HMSE#TRPBF LT8364IDE#PBF LT8364IDE#PBF LT8364IDE#TRPBF LT8364IDE#TRPBF LT8364IMSE#PBF LT8364IMSE#PBF LT8364IMSE#TRPBF LT8364IMSE#TRPBF
Text Version of Document
LT8364
APPLICATIONS INFORMATION ACHIEVING ULTRALOW QUIESCENT CURRENT
To enhance efficiency at light loads the LT8364 uses a low ripple Burst Mode architecture. This keeps the out- IL put capacitor charged to the desired output voltage while 1A/DIV minimizing the input quiescent current and output ripple. In Burst Mode operation, the LT8364 delivers single small VOUT pulses of current to the output capacitor followed by sleep 20mV/DIV periods where the output power is supplied by the output 8364 F02 capacitor. While in sleep mode, the LT8364 consumes 10µs/DIV only 9µA.
Figure 2. Burst Mode Operation
As the output load decreases, the frequency of single cur- rent pulses decreases (see Figure 1) and the percentage of defined by the resistor at the RT pin as shown in Figure 1. time the LT8364 is in sleep mode increases, resulting in The output load at which the LT8364 reaches the fixed much higher light load efficiency than for typical convert- frequency varies based on input voltage, output voltage, ers. To optimize the quiescent current performance at light and inductor choice. loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current.
PROGRAMMING INPUT TURN-ON AND TURN-OFF
In addition, all possible leakage currents from the output
THRESHOLDS WITH EN/UVLO PIN
should also be minimized as they all add to the equiva- The EN/UVLO pin voltage controls whether the LT8364 is lent output load. The largest contributor to leakage current enabled or is in a shutdown state. A 1.6V reference and can be due to the reverse biased leakage of the Schottky a comparator A6 with built-in hysteresis (typical 80mV) diode (see Diode Selection in the Applications Information allow the user to accurately program the system input section). voltage at which the IC turns on and off (see the Block While in Burst Mode operation, the current limit of the Diagram). The typical input falling and rising threshold switch is approximately 1A resulting in the output voltage voltages can be calculated by the following equations: ripple shown in Figure 2. Increasing the output capaci- tance wil decrease the output ripple proportional y. As VIN(FALLING,UVLO(–)) = 1.60 • R3 + R4 the output load ramps upward from zero the switching R4 frequency will increase but only up to the fixed frequency V IN(RISING, UVLO(+)) = 1.68 • R3 + R4 R4 2.5 FRONT PAGE APPLICATION VIN current is reduced below 1µA when the EN/UVLO pin VIN = 12V 2.0 V voltage is less than 0.2V. The EN/UVLO pin can be con- OUT = 48V nected directly to the input supply VIN for always-enabled 1.5 operation. A logic input can also control the EN/UVLO pin. When operating in Burst Mode operation for light load 1.0 currents, the current through the R3 and R4 network can easily be greater than the supply current consumed by the 0.5 SWITCHING FREQUENCY (MHz) LT8364. Therefore, R3 and R4 should be large enough to 0 minimize their effect on efficiency at light loads. 0 20 40 60 80 100 LOAD CURRENT (mA) 8364 F01
Figure 1. Burst Frequency vs Load Current
8364f 10 For more information www.linear.com/LT8364 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM OPERATION APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION TYPICAL APPLICATION RELATED PARTS
APPLICATIONS INFORMATION ACHIEVING ULTRALOW QUIESCENT CURRENT
To enhance efficiency at light loads the LT8364 uses a low ripple Burst Mode architecture. This keeps the out- IL put capacitor charged to the desired output voltage while 1A/DIV minimizing the input quiescent current and output ripple. In Burst Mode operation, the LT8364 delivers single small VOUT pulses of current to the output capacitor followed by sleep 20mV/DIV periods where the output power is supplied by the output 8364 F02 capacitor. While in sleep mode, the LT8364 consumes 10µs/DIV only 9µA.
Figure 2. Burst Mode Operation
As the output load decreases, the frequency of single cur- rent pulses decreases (see Figure 1) and the percentage of defined by the resistor at the RT pin as shown in Figure 1. time the LT8364 is in sleep mode increases, resulting in The output load at which the LT8364 reaches the fixed much higher light load efficiency than for typical convert- frequency varies based on input voltage, output voltage, ers. To optimize the quiescent current performance at light and inductor choice. loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current.
PROGRAMMING INPUT TURN-ON AND TURN-OFF
In addition, all possible leakage currents from the output
THRESHOLDS WITH EN/UVLO PIN
should also be minimized as they all add to the equiva- The EN/UVLO pin voltage controls whether the LT8364 is lent output load. The largest contributor to leakage current enabled or is in a shutdown state. A 1.6V reference and can be due to the reverse biased leakage of the Schottky a comparator A6 with built-in hysteresis (typical 80mV) diode (see Diode Selection in the Applications Information allow the user to accurately program the system input section). voltage at which the IC turns on and off (see the Block While in Burst Mode operation, the current limit of the Diagram). The typical input falling and rising threshold switch is approximately 1A resulting in the output voltage voltages can be calculated by the following equations: ripple shown in Figure 2. Increasing the output capaci- tance wil decrease the output ripple proportional y. As VIN(FALLING,UVLO(–)) = 1.60 • R3 + R4 the output load ramps upward from zero the switching R4 frequency will increase but only up to the fixed frequency V IN(RISING, UVLO(+)) = 1.68 • R3 + R4 R4 2.5 FRONT PAGE APPLICATION VIN current is reduced below 1µA when the EN/UVLO pin VIN = 12V 2.0 V voltage is less than 0.2V. The EN/UVLO pin can be con- OUT = 48V nected directly to the input supply VIN for always-enabled 1.5 operation. A logic input can also control the EN/UVLO pin. When operating in Burst Mode operation for light load 1.0 currents, the current through the R3 and R4 network can easily be greater than the supply current consumed by the 0.5 SWITCHING FREQUENCY (MHz) LT8364. Therefore, R3 and R4 should be large enough to 0 minimize their effect on efficiency at light loads. 0 20 40 60 80 100 LOAD CURRENT (mA) 8364 F01
Figure 1. Burst Frequency vs Load Current
8364f 10 For more information www.linear.com/LT8364 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM OPERATION APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION TYPICAL APPLICATION RELATED PARTS
