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LTC3425 Datasheet(PDF) 8 Page - Linear Technology |
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LTC3425 Datasheet(HTML) 8 Page - Linear Technology |
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8 / 24 page  LTC3425 8 3425f PI FU CTIO S GNDA–D (Pins 1, 2, 7, 8, 17, 18, 23, 24): Power Ground for the IC and the Four Internal N-channel MOSFETs. Connect directly to the power ground plane. SWA–D (Pins 3, 6, 19, 22): Switch Pins. Connect induc- tors here. Minimize trace length to keep EMI to a mini- mum. For discontinuous inductor current, a controlled impedance is internally connected from SW to VIN to minimize EMI. For applications where VOUT > 4.3V, it is required to have Schottky diodes from SW to VOUT or a snubber circuit to stay within absolute maximum rating on the SW pins. VOUTA–D (Pins 4, 5, 20, 21): Output of the Four Synchro- nous Rectifiers. Connect output filter capacitors to these pins. Connect one low ESR ceramic capacitor directly from each pin to the ground plane. REFEN (Pin 9): Pull this pin above 1.4V to enable the REF output. Grounding this pin turns the REF output off to reduce quiescent current. VOUTS (Pin 10): VOUT Sense Pin. Connect VOUTS directly to an output filter capacitor. The top of the feedback divider network should also be tied to this point. SGND (Pin 11): Signal Ground Pin. Connect to ground plane, near the feedback divider resistor. FB (Pin 12): Feedback Pin. Connect FB to a resistor divider, keeping the trace as short as possible. The output voltage can be adjusted according to the following formula: V RR R OUT = + 122 12 1 .• where R1 is connected from FB to SGND and R2 is connected from FB to VOUTS. COMP (Pin 13): Error Amp Output. A frequency compen- sation network is connected from this pin to ground to compensate the loop. See the section Closing the Feed- back Loop for guidelines. BURST (Pin 14): Burst Mode Threshold Adjust Pin. A resistor/capacitor combination from this pin to ground programs the average load current at which automatic Burst Mode operation is entered. For manual control of Burst Mode operation, ground BURST to force Burst Mode operation or connect it to VOUT to force fixed frequency PWM mode. Note that BURST must not be pulled higher than VOUT. REFOUT (Pin 15): Buffered 1.22V Reference Output. This pin can source up to 100 µA and sink up to 10µA (only active when REFEN is pulled high). This pin must be decoupled with a 0.1 µF capacitor for stability. PGOOD (Pin 16): Open-Drain Output of the Power Good Comparator. This pin will go low when the output voltage drops 11% below its regulated value. Maximum sink current should be limited to 10mA. SYNCOUT (Pin 25): Sync Output Pin. A clock is provided at the oscillator frequency, but phase-shifted 180 degrees to allow for synchronizing two devices for an 8-phase converter. CCM (Pin 26): This pin is used to select forced continuous conduction mode. Normally this pin is grounded to allow CCM or DCM operation. To force continuous conduction mode, tie this pin to VOUT. In this mode, a reverse current of up to about 0.6A will be allowed before turning off the synchronous rectifier. This will prevent pulse skipping at light load when Burst Mode operation is disabled, and will also improve the large-signal transient response when going from a heavy load to a light load. For Burst Mode operation, CCM should be low. |
Similar Part No. - LTC3425_15 |
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Similar Description - LTC3425_15 |
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