Datasheet LTC3646, LTC3646-1 (Analog Devices) - 7

LTC3646/LTC3646-1
PIN FUNCTIONS (DFN/MSOP) SGND (Pin 1/Pin 1):
Analog Ground Pin. This pin should
PVIN (Pin 8/Pins 9, 10):
Supply Pin for the Power Switch. have a low noise connection to the reference ground. This pin connects directly to top switch. Closely decouple
V
this pin to PGND with a 10µF or greater, low ESR capacitor.
FB (Pin 2/Pin 2):
Output Voltage Feedback Pin. Input to the error amplifier that compares the feedback voltage with
SW (Pin 9/Pin 11):
Switch Node Output Pin. Connect this the internal 0.6V reference. Connect this pin to a resistor pin to the switch side of the external inductor and boost divider network to program the desired output voltage. capacitor.
ITH (Pin 3/Pin 3):
Error Amplifier Output and Switching
BOOST (Pin 10/Pin 12):
Boosted Supply Pin. A boosted Regulator Compensation Point. Connect this pin to appro- voltage is generated at this pin by connecting a capacitor priate external components to compensate the regulator between this pin and the SW pin. The normal operation loop frequency response. Connect this pin to INTVCC to voltage swing of this pin ranges from INTVCC to PVIN use the default internal compensation. + INTVCC. When necessary, connect the cathode of an
RT (Pin 4/Pin 4):
Oscillator Frequency Program Pin. Con- external boost diode to this pin. See the Boost Capacitor nect an external resistor between 450k and 30k from this and Diode section. pin to SGND to program the switching frequency from
INTVCC (Pin 11/Pin 13):
Internal 5.0V Regulator Output 200kHz to 3.0MHz. When RT is connected to INTVCC, the Pin. This pin should be decoupled to PGND with a 4.7µF or switching frequency will be 2.25MHz. Do not float RT. greater low ESR capacitor. When necessary, connect the
V
anode of an external boost diode to this pin. The internal
ON (Pin 5/Pin 5):
On-Time Voltage Input Pin. This pin provides information about the output voltage (V regulator is disabled when the RUN pin is low. OUT) to the on-time control loop. Connect this pin to the regulated
EXTVCC (Pin 12/Pin 14):
Use this input pin to power the output to make the on-time proportional to the output chip’s low voltage control circuitry if a high efficiency voltage. supply between 4.5V and 6.0V is available. Otherwise,
PGOOD (Pin 6/Pin 6):
Power Good Output Pin. PGOOD connect this pin to SGND. See the Applications Informa- is pulled to ground when the voltage at the V tion section for further information. FB pin is not within 7.5% (typical) of the internal 0.6V reference. PGOOD
RUN (Pin 13/Pin 15):
Regulator Enable Pin. Enables chip becomes high impedance once the voltage at the VFB pin operation by applying a voltage greater than VRUN. returns to within 5% of the internal reference.
SVIN (Pin 14/Pin 16):
Power Supply Input for Internal
MODE/SYNC (Pin 7/Pin 7):
Mode Selection and External Circuitry. Closely decouple this pin to SGND with a greater Clock Input Pin. This pin forces the LTC3646 into forced than 1µF low ESR capacitor. SVIN pin voltage should equal continuous operation when tied to ground, and high ef- PVIN in order to correctly calculate on the on time and ficiency Burst Mode operation when tied to INTVCC. When maintain constant frequency operation. driven with an external clock, the LTC3646 will adjust the
PGND (Exposed Pad Pin 15/Exposed Pad Pin 17):
Power top switch on-time to match the switching frequency to Ground Pin. The exposed pad must be well soldered to the applied clock frequency and the part will operate in the PCB ground to provide a low impedance electrical forced continuous mode. During start-up or external clock connection to ground and rated thermal performance. synchronization, the operating mode will be as described in the Applications Information section. 36461fc For more information www.linear.com/LTC3646 7 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Typical Application Related Parts