Datasheet LT3570 (Analog Devices) - 7

LT3570
PIN FUNCTIONS (QFN/TSSOP) VIN2 (Pins 1,2/Pin 14):
Input Voltage for the Buck Regulator.
SHDN3 (Pin13/Pin 4):
Shutdown Pin. Tie to 1.5V or more This pin also supplies the current to the internal circuitry to enable the NPN LDO. Tie all SHDN pins to 0.3V or less of the LT3570. This pin must be locally bypassed with a to shutdown the part. capacitor.
SYNC (Pin 14/Pin 5):
Synchronization Pin. The SYNC pin
SW2 (Pin 3/Pin15):
Switch Node. This pin connects to is used to synchronize the internal oscillator to an exter- the emitter of an internal NPN power switch. Connect a nal signal. The synchronizing range is equal to the initial diode, inductor and boost capacitor to this pin to form operating frequency set by the RT pin up to 1.3 times the the buck regulator. initial operating frequency.
SW1 (Pin 4/Pin16):
Switch Node. This pin connects to the
RT (Pin 15/Pin 6):
Frequency Set Pin. Place a resistor to collector of an internal NPN power switch. Connect a diode GND to set the internal frequency. The range of oscillation and inductor to this pin to form the boost regulator. is 500kHz to 2MHz.
GND (Pins 5, 6, 16, 25/Pins 17, 21):
Ground. The Exposed
SS2 (Pin 17/Pin 7):
Soft-Start Pin. Place a soft-start Pad of the package provides both electrical contact to capacitor here. Upon start-up, a current charges the ground and good thermal contact to the printed circuit capacitor to 2V. This pin ramps the reference voltage of board. The Exposed Pad must be soldered to the circuit the buck switcher. board for proper operation.
VC2 (Pin 18/Pin 8):
Control Voltage and Compensation Pin
VIN1 (Pin 7/Pin18):
Input Voltage for the Boost Regulator. for the Internal Error Amplifi er. Connect a series RC from This pin supplies current to drive the boost NPN transistor this pin to ground to compensate the switching regulator of the LT3570. This pin must be locally bypassed with a loop for the buck regulator. capacitor.
FB2 (Pin 19/Pin 9):
Feedback Pin. The LT3570 regulates
SS1 (Pin 8/Pin 19):
Soft-Start Pin. Place a soft-start this pin to 788mV. Connect the feedback resistors to capacitor here. Upon start-up, a current charges the this pin to set the output voltage for the buck switching capacitor to 2V. This pin ramps the reference voltage of regulator. the boost switcher.
FB3 (Pin 20/Pin 10):
Feedback Pin. The LT3570 regulates
VC1 (Pin 9/Pin 20):
Control Voltage and Compensation Pin this pin to 788mV. Connect the feedback resistors to this for the Internal Error Amplifi er. Connect a series RC from pin to set the output voltage for the LDO controller. this pin to ground to compensate the switching regulator
NPN_DRIVE (Pin 21/Pin 11):
Base Drive for the External loop for the boost regulator. NPN. This pin provides a bias current to drive the base of
FB1 (Pin 10/Pin 1):
Feedback Pin. The LT3570 regulates the NPN. This base current is driven from the IN3 supply this pin to 788mV. Connect the feedback resistors to voltage. this pin to set the output voltage for the boost switching
V
regulator.
IN3 (Pin 22/Pin 12):
Input Voltage for the NPN LDO. This pin supplies current to drive the base of the NPN. This pin
SHDN1 (Pin 11/Pin 2):
Shutdown Pin. Tie to 1.4V or more must be locally bypassed with a capacitor. to enable the boost switcher. Tie all SHDN pins to 0.3V or
BIAS (Pin 23):
QFN Package Only. This pin supplies current less to shutdown the part. to the internal circuitry of the LT3570 if greater than 2.5V.
SHDN2 (Pin 12/Pin 3):
Shutdown Pin. Tie to 1.4V or more This pin must be locally bypassed with a capacitor. to enable the buck switcher. Tie all SHDN pins to 0.3V or
BOOST (Pin 24/Pin 13):
Bias for the Base Drive of the less to shutdown the part. NPN Switch for the Buck Regulator. This pin provides a bias voltage higher than VIN2. The voltage on this pin is charged up through an external Schottky diode. 3570fb 7