Datasheet MAX1795, MAX1796, MAX1797 (Maxim) - 9
| 制造商 | Maxim |
| 描述 | Low-Supply Current, Step-Up DC-DC Converters with True Shutdown |
| 页数 / 页 | 13 / 9 — MAX1795. MAX1796. MAX1797. Synchronous Rectification. BATT/Damping … |
| 文件格式/大小 | PDF / 2.1 Mb |
| 文件语言 | 英语 |
MAX1795. MAX1796. MAX1797. Synchronous Rectification. BATT/Damping Switch. Shutdown
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link to page 5 link to page 10 link to page 10 MAX1795/MAX1796/ Low-Supply Current, Step-Up DC-DC Converters MAX1797 with True Shutdown BATT R1 1M SHDN ZERO-
MAX1795
CROSSING LBO
MAX1796
AMPLIFIER LBI
MAX1797
S + Q OUT _ OUT R BODY 47µF 0.85V DIODE S CONTROL Q BATT BATT R 22µH TIMER BLOCK 47F S Q LX R START TON MAX TOFF MAX OUT R2 FB FB SELECT CURRENT-LIMIT ERROR AMPLIFIER R3 REFERENCE AMPLIFIER GND Figure 2. Functional Diagram
Synchronous Rectification
impedance node. The LBI/LBO comparator remains The internal synchronous rectifier eliminates the need active in shutdown. for an external Schottky diode, reducing cost and board As shown in Figure 1, the MAX1795/MAX1796/MAX1797 space. During the cycle off-time, the P-channel MOSFET can be automatically shut down when the input voltage turns on and shunts the MOSFET body diode. As a drops below a preset threshold by connecting LBO to result, the synchronous rectifier significantly improves SHDN (see the Low-Battery Detection section). efficiency without the addition of an external component. Conversion efficiency can be as high as 95%, as shown
BATT/Damping Switch
in the Typical Operating Characteristics section. The MAX1795/MAX1796/MAX1797 each contain an inter- nal damping switch to minimize ringing at LX. The damp-
Shutdown
ing switch connects a resistor across the inductor when The device enters shutdown when VSHDN is high, the inductor’s energy is depleted (Figure 3). Normally, reducing supply current to less than 2μA. During shut- when the energy in the inductor is insufficient to supply down, the synchronous rectifier disconnects the output current to the output, the capacitance and inductance at from the input, eliminating the DC conduction path LX form a resonant circuit that causes ringing. The ringing that normally exists with traditional boost converters in continues until the energy is dissipated through the series shutdown mode. In shutdown, OUT becomes a high- resistance of the inductor. The damping switch supplies a www.maximintegrated.com Maxim Integrated │ 9
MAX1795
CROSSING LBO
MAX1796
AMPLIFIER LBI
MAX1797
S + Q OUT _ OUT R BODY 47µF 0.85V DIODE S CONTROL Q BATT BATT R 22µH TIMER BLOCK 47F S Q LX R START TON MAX TOFF MAX OUT R2 FB FB SELECT CURRENT-LIMIT ERROR AMPLIFIER R3 REFERENCE AMPLIFIER GND Figure 2. Functional Diagram
Synchronous Rectification
impedance node. The LBI/LBO comparator remains The internal synchronous rectifier eliminates the need active in shutdown. for an external Schottky diode, reducing cost and board As shown in Figure 1, the MAX1795/MAX1796/MAX1797 space. During the cycle off-time, the P-channel MOSFET can be automatically shut down when the input voltage turns on and shunts the MOSFET body diode. As a drops below a preset threshold by connecting LBO to result, the synchronous rectifier significantly improves SHDN (see the Low-Battery Detection section). efficiency without the addition of an external component. Conversion efficiency can be as high as 95%, as shown
BATT/Damping Switch
in the Typical Operating Characteristics section. The MAX1795/MAX1796/MAX1797 each contain an inter- nal damping switch to minimize ringing at LX. The damp-
Shutdown
ing switch connects a resistor across the inductor when The device enters shutdown when VSHDN is high, the inductor’s energy is depleted (Figure 3). Normally, reducing supply current to less than 2μA. During shut- when the energy in the inductor is insufficient to supply down, the synchronous rectifier disconnects the output current to the output, the capacitance and inductance at from the input, eliminating the DC conduction path LX form a resonant circuit that causes ringing. The ringing that normally exists with traditional boost converters in continues until the energy is dissipated through the series shutdown mode. In shutdown, OUT becomes a high- resistance of the inductor. The damping switch supplies a www.maximintegrated.com Maxim Integrated │ 9