Datasheet LTC3425 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | 5A, 8MHz, 4-Phase Synchronous Step-Up DC/DC Converter |
| Pages / Page | 24 / 8 — PI FU CTIO S. GNDA–D (Pins 1, 2, 7, 8, 17, 18, 23, 24):. COMP (Pin 13):. … |
| File Format / Size | PDF / 284 Kb |
| Document Language | English |
PI FU CTIO S. GNDA–D (Pins 1, 2, 7, 8, 17, 18, 23, 24):. COMP (Pin 13):. SWA–D (Pins 3, 6, 19, 22):. BURST (Pin 14):
Model Line for this Datasheet
Text Version of Document
LTC3425
U U U PI FU CTIO S GNDA–D (Pins 1, 2, 7, 8, 17, 18, 23, 24):
Power Ground
COMP (Pin 13):
Error Amp Output. A frequency compen- for the IC and the Four Internal N-channel MOSFETs. sation network is connected from this pin to ground to Connect directly to the power ground plane. compensate the loop. See the section Closing the Feed- back Loop for guidelines.
SWA–D (Pins 3, 6, 19, 22):
Switch Pins. Connect induc- tors here. Minimize trace length to keep EMI to a mini-
BURST (Pin 14):
Burst Mode Threshold Adjust Pin. A mum. For discontinuous inductor current, a controlled resistor/capacitor combination from this pin to ground impedance is internally connected from SW to VIN to programs the average load current at which automatic minimize EMI. For applications where VOUT > 4.3V, it is Burst Mode operation is entered. required to have Schottky diodes from SW to VOUT or a For manual control of Burst Mode operation, ground snubber circuit to stay within absolute maximum rating on BURST to force Burst Mode operation or connect it to VOUT the SW pins. to force fixed frequency PWM mode. Note that BURST
V
must not be pulled higher than V
OUTA–D (Pins 4, 5, 20, 21):
Output of the Four Synchro- OUT. nous Rectifiers. Connect output filter capacitors to these
REFOUT (Pin 15):
Buffered 1.22V Reference Output. This pins. Connect one low ESR ceramic capacitor directly pin can source up to 100µA and sink up to 10µA (only from each pin to the ground plane. active when REFEN is pulled high). This pin must be
REFEN (Pin 9):
Pull this pin above 1.4V to enable the REF decoupled with a 0.1µF capacitor for stability. output. Grounding this pin turns the REF output off to
PGOOD (Pin 16):
Open-Drain Output of the Power Good reduce quiescent current. Comparator. This pin will go low when the output voltage
V
drops 11% below its regulated value. Maximum sink
OUTS (Pin 10):
VOUT Sense Pin. Connect VOUTS directly to an output filter capacitor. The top of the feedback divider current should be limited to 10mA. network should also be tied to this point.
SYNCOUT (Pin 25):
Sync Output Pin. A clock is provided
SGND (Pin 11):
Signal Ground Pin. Connect to ground at the oscillator frequency, but phase-shifted 180 degrees plane, near the feedback divider resistor. to allow for synchronizing two devices for an 8-phase converter.
FB (Pin 12):
Feedback Pin. Connect FB to a resistor divider, keeping the trace as short as possible. The output voltage
CCM (Pin 26):
This pin is used to select forced continuous can be adjusted according to the following formula: conduction mode. Normally this pin is grounded to allow CCM or DCM operation. To force continuous conduction R1 R2 mode, tie this pin to V V OUT. In this mode, a reverse current OUT = + 1 2 . 2 • R1 of up to about 0.6A will be allowed before turning off the synchronous rectifier. This will prevent pulse skipping at where R1 is connected from FB to SGND and R2 is light load when Burst Mode operation is disabled, and will connected from FB to VOUTS. 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. 3425f 8
U U U PI FU CTIO S GNDA–D (Pins 1, 2, 7, 8, 17, 18, 23, 24):
Power Ground
COMP (Pin 13):
Error Amp Output. A frequency compen- for the IC and the Four Internal N-channel MOSFETs. sation network is connected from this pin to ground to Connect directly to the power ground plane. compensate the loop. See the section Closing the Feed- back Loop for guidelines.
SWA–D (Pins 3, 6, 19, 22):
Switch Pins. Connect induc- tors here. Minimize trace length to keep EMI to a mini-
BURST (Pin 14):
Burst Mode Threshold Adjust Pin. A mum. For discontinuous inductor current, a controlled resistor/capacitor combination from this pin to ground impedance is internally connected from SW to VIN to programs the average load current at which automatic minimize EMI. For applications where VOUT > 4.3V, it is Burst Mode operation is entered. required to have Schottky diodes from SW to VOUT or a For manual control of Burst Mode operation, ground snubber circuit to stay within absolute maximum rating on BURST to force Burst Mode operation or connect it to VOUT the SW pins. to force fixed frequency PWM mode. Note that BURST
V
must not be pulled higher than V
OUTA–D (Pins 4, 5, 20, 21):
Output of the Four Synchro- OUT. nous Rectifiers. Connect output filter capacitors to these
REFOUT (Pin 15):
Buffered 1.22V Reference Output. This pins. Connect one low ESR ceramic capacitor directly pin can source up to 100µA and sink up to 10µA (only from each pin to the ground plane. active when REFEN is pulled high). This pin must be
REFEN (Pin 9):
Pull this pin above 1.4V to enable the REF decoupled with a 0.1µF capacitor for stability. output. Grounding this pin turns the REF output off to
PGOOD (Pin 16):
Open-Drain Output of the Power Good reduce quiescent current. Comparator. This pin will go low when the output voltage
V
drops 11% below its regulated value. Maximum sink
OUTS (Pin 10):
VOUT Sense Pin. Connect VOUTS directly to an output filter capacitor. The top of the feedback divider current should be limited to 10mA. network should also be tied to this point.
SYNCOUT (Pin 25):
Sync Output Pin. A clock is provided
SGND (Pin 11):
Signal Ground Pin. Connect to ground at the oscillator frequency, but phase-shifted 180 degrees plane, near the feedback divider resistor. to allow for synchronizing two devices for an 8-phase converter.
FB (Pin 12):
Feedback Pin. Connect FB to a resistor divider, keeping the trace as short as possible. The output voltage
CCM (Pin 26):
This pin is used to select forced continuous can be adjusted according to the following formula: conduction mode. Normally this pin is grounded to allow CCM or DCM operation. To force continuous conduction R1 R2 mode, tie this pin to V V OUT. In this mode, a reverse current OUT = + 1 2 . 2 • R1 of up to about 0.6A will be allowed before turning off the synchronous rectifier. This will prevent pulse skipping at where R1 is connected from FB to SGND and R2 is light load when Burst Mode operation is disabled, and will connected from FB to VOUTS. 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. 3425f 8
