Datasheet LT1776 (Analog Devices) - 5
| Manufacturer | Analog Devices |
| Description | Wide Input Range, High Efficiency, Step-Down Switching Regulator |
| Pages / Page | 20 / 5 — TYPICAL PERFORMANCE CHARACTERISTICS. VC Pin Switching Threshold,. Boost … |
| File Format / Size | PDF / 235 Kb |
| Document Language | English |
TYPICAL PERFORMANCE CHARACTERISTICS. VC Pin Switching Threshold,. Boost Threshold, Clamp Voltage. Feedback Amplifier Output
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Text Version of Document
LT1776
W U TYPICAL PERFORMANCE CHARACTERISTICS VC Pin Switching Threshold, Boost Threshold, Clamp Voltage Feedback Amplifier Output Error Amplifier Transconductance vs Temperature Current vs FB Pin Voltage vs Temperature
2.2 750 µA) 100 25°C 2.0 –55°C 700 CLAMP 50 125°C 1.8 VOLTAGE µmho) 650 0 1.6 600 BOOST 1.4 THRESHOLD 550 –50 PIN VOLTAGE (V) CV 1.2 SWITCHING 500 THRESHOLD –100 TRANSCONDUCTANCE ( 1.0 450 0.8 FEEDBACK AMPLIFIER OUTPUT CURRENT ( –150 400 –50 –25 0 25 50 75 100 125 1.0 1.1 1.2 1.3 1.4 1.5 –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) FB PIN VOLTAGE (V) TEMPERATURE (°C) LT1776 G10 1776 G11 LT1776 G12
U U U PIN FUNCTIONS SHDN (Pin 1):
When pulled below the shutdown mode If the output capacitor is located more than one inch from threshold, nominally 0.30V, this pin turns off the regulator the VCC pin, a separate 0.1µF bypass capacitor to ground and reduces VIN input current to a few tens of microam- may be required right at the pin. peres (shutdown mode).
VSW (Pin 3):
This is the emitter node of the output switch When this pin is held above the shutdown mode threshold, and has large currents flowing through it. This node but below the lockout threshold, the part will be opera- moves at a high dV/dt rate, especially when in “boost” tional with the exception that output switching action will mode. Keep the traces to the switching components as be inhibited (lockout mode). A user-adjustable undervolt- short as possible to minimize electromagnetic radiation age lockout can be implemented by driving this pin from and voltage spikes. an external resistor divider to VIN. This action is logically
GND (Pin 4):
This is the device ground pin. The internal “ANDed” with the internal UVLO, set at nominally 6.7V, reference and feedback amplifier are referred to it. Keep such that minimum VIN can be increased above 6.7V, but the ground path connection to the FB divider and the V not decreased (see Applications Information). C compensation capacitor free of large ground currents. If unused, this pin should be left open. However, the high
V
impedance nature of this pin renders it susceptible to
IN (Pin 5):
This is the high voltage supply pin for the output switch. It also supplies power to the internal control coupling from the high speed VSW node, so a small circuitry during start-up conditions or if the V capacitor to ground, typically 100pF or so is recom- CC pin is left open. A high quality bypass capacitor which meets the mended when the pin is left “open”. input ripple current requirements is needed here. (See
VCC (Pin 2):
This pin is used to power the internal control Applications Information). circuitry off of the switching supply output. Proper use of
SYNC (Pin 6):
Pin used to synchronize internal oscillator this pin enhances overall power supply efficiency. During to the external frequency reference. It is directly logic start-up conditions, internal control circuitry is powered compatible and can be driven with any signal between directly from VIN. 5
W U TYPICAL PERFORMANCE CHARACTERISTICS VC Pin Switching Threshold, Boost Threshold, Clamp Voltage Feedback Amplifier Output Error Amplifier Transconductance vs Temperature Current vs FB Pin Voltage vs Temperature
2.2 750 µA) 100 25°C 2.0 –55°C 700 CLAMP 50 125°C 1.8 VOLTAGE µmho) 650 0 1.6 600 BOOST 1.4 THRESHOLD 550 –50 PIN VOLTAGE (V) CV 1.2 SWITCHING 500 THRESHOLD –100 TRANSCONDUCTANCE ( 1.0 450 0.8 FEEDBACK AMPLIFIER OUTPUT CURRENT ( –150 400 –50 –25 0 25 50 75 100 125 1.0 1.1 1.2 1.3 1.4 1.5 –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) FB PIN VOLTAGE (V) TEMPERATURE (°C) LT1776 G10 1776 G11 LT1776 G12
U U U PIN FUNCTIONS SHDN (Pin 1):
When pulled below the shutdown mode If the output capacitor is located more than one inch from threshold, nominally 0.30V, this pin turns off the regulator the VCC pin, a separate 0.1µF bypass capacitor to ground and reduces VIN input current to a few tens of microam- may be required right at the pin. peres (shutdown mode).
VSW (Pin 3):
This is the emitter node of the output switch When this pin is held above the shutdown mode threshold, and has large currents flowing through it. This node but below the lockout threshold, the part will be opera- moves at a high dV/dt rate, especially when in “boost” tional with the exception that output switching action will mode. Keep the traces to the switching components as be inhibited (lockout mode). A user-adjustable undervolt- short as possible to minimize electromagnetic radiation age lockout can be implemented by driving this pin from and voltage spikes. an external resistor divider to VIN. This action is logically
GND (Pin 4):
This is the device ground pin. The internal “ANDed” with the internal UVLO, set at nominally 6.7V, reference and feedback amplifier are referred to it. Keep such that minimum VIN can be increased above 6.7V, but the ground path connection to the FB divider and the V not decreased (see Applications Information). C compensation capacitor free of large ground currents. If unused, this pin should be left open. However, the high
V
impedance nature of this pin renders it susceptible to
IN (Pin 5):
This is the high voltage supply pin for the output switch. It also supplies power to the internal control coupling from the high speed VSW node, so a small circuitry during start-up conditions or if the V capacitor to ground, typically 100pF or so is recom- CC pin is left open. A high quality bypass capacitor which meets the mended when the pin is left “open”. input ripple current requirements is needed here. (See
VCC (Pin 2):
This pin is used to power the internal control Applications Information). circuitry off of the switching supply output. Proper use of
SYNC (Pin 6):
Pin used to synchronize internal oscillator this pin enhances overall power supply efficiency. During to the external frequency reference. It is directly logic start-up conditions, internal control circuitry is powered compatible and can be driven with any signal between directly from VIN. 5
