Datasheet LT3970 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | 40V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes |
| Pages / Page | 22 / 8 — pin FuncTions. FB (Pin 1, LT3970 Only):. GND (Pins 4, 5, Exposed Pad (Pin … |
| File Format / Size | PDF / 330 Kb |
| Document Language | English |
pin FuncTions. FB (Pin 1, LT3970 Only):. GND (Pins 4, 5, Exposed Pad (Pin 11, DFN Only)):. SW (Pin 6):
Model Line for this Datasheet
LT3970 Series
Text Version of Document
LT3970 Series
pin FuncTions FB (Pin 1, LT3970 Only):
The LT3970 Regulates the FB
GND (Pins 4, 5, Exposed Pad (Pin 11, DFN Only)):
Ground. Pin to 1.21V. Connect the feedback resistor divider tap to Must be soldered to PCB. this pin.
SW (Pin 6):
The SW pin is the output of an internal power
VOUT (Pin 1, LT3970-X Only):
The LT3970-3.3, LT3970-3.42 switch. Connect this pin to the inductor. and LT3970-5 regulate the VOUT Pin to 3.3V, 3.42V and 5V
BOOST (Pin 7):
This pin is used to provide a drive volt- respectively. This pin connects to the internal feedback age, higher than the input voltage, to the internal bipolar divider that programs the fixed output voltage. NPN power switch.
EN (Pin 2):
The part is in shutdown when this pin is low
BD (Pin 8):
This pin connects to the anode of the boost and active when this pin is high. The hysteretic threshold diode. This pin also supplies current to the LT3970’s internal voltage is 1V going up and 0.97V going down. Tie to VIN regulator when BD is above 3.2V. if shutdown feature is not used. The EN threshold is ac- curate only when VIN is above 4.2V. If VIN is lower than
PG (Pin 9):
The PG pin is the open-drain output of an 4.2V, ground EN to place the part in shutdown. internal comparator. PG remains low until the FB pin is within 10% of the final regulation voltage. PG is valid when
VIN (Pin 3):
The VIN pin supplies current to the LT3970’s V internal circuitry and to the internal power switch. This IN is above 4.2V and EN is high. pin must be locally bypassed.
RT (Pin 10):
A resistor is tied between RT and ground to set the switching frequency.
block Diagram
V V IN IN 3 C1 INTERNAL 1.21V REF – 1V + BD 8 EN SHDN + 2 – DBOOST SLOPE COMP SWITCH LATCH BOOST 7 R RT OSCILLATOR Q 10 200kHz TO 2.2MHz C3 S RT PG 9 + 1.09V + SW L1 ERROR VC Burst Mode 6 VOUT AMP DETECT DCATCH C2 – – R2 R1 LT3970 ONLY GND LT3970-X FB (4, 5) V ONLY* OUT 1 1 R2 R1 3990 BD * LT3970-3.3: R1 = 12.65M, R2 = 7.35M LT3970-3.42: R1 = 12.65M, R2 = 6.93M LT3970-5: R1 = 15.15M, R2 = 4.85M 3970fc 8 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Related Parts
pin FuncTions FB (Pin 1, LT3970 Only):
The LT3970 Regulates the FB
GND (Pins 4, 5, Exposed Pad (Pin 11, DFN Only)):
Ground. Pin to 1.21V. Connect the feedback resistor divider tap to Must be soldered to PCB. this pin.
SW (Pin 6):
The SW pin is the output of an internal power
VOUT (Pin 1, LT3970-X Only):
The LT3970-3.3, LT3970-3.42 switch. Connect this pin to the inductor. and LT3970-5 regulate the VOUT Pin to 3.3V, 3.42V and 5V
BOOST (Pin 7):
This pin is used to provide a drive volt- respectively. This pin connects to the internal feedback age, higher than the input voltage, to the internal bipolar divider that programs the fixed output voltage. NPN power switch.
EN (Pin 2):
The part is in shutdown when this pin is low
BD (Pin 8):
This pin connects to the anode of the boost and active when this pin is high. The hysteretic threshold diode. This pin also supplies current to the LT3970’s internal voltage is 1V going up and 0.97V going down. Tie to VIN regulator when BD is above 3.2V. if shutdown feature is not used. The EN threshold is ac- curate only when VIN is above 4.2V. If VIN is lower than
PG (Pin 9):
The PG pin is the open-drain output of an 4.2V, ground EN to place the part in shutdown. internal comparator. PG remains low until the FB pin is within 10% of the final regulation voltage. PG is valid when
VIN (Pin 3):
The VIN pin supplies current to the LT3970’s V internal circuitry and to the internal power switch. This IN is above 4.2V and EN is high. pin must be locally bypassed.
RT (Pin 10):
A resistor is tied between RT and ground to set the switching frequency.
block Diagram
V V IN IN 3 C1 INTERNAL 1.21V REF – 1V + BD 8 EN SHDN + 2 – DBOOST SLOPE COMP SWITCH LATCH BOOST 7 R RT OSCILLATOR Q 10 200kHz TO 2.2MHz C3 S RT PG 9 + 1.09V + SW L1 ERROR VC Burst Mode 6 VOUT AMP DETECT DCATCH C2 – – R2 R1 LT3970 ONLY GND LT3970-X FB (4, 5) V ONLY* OUT 1 1 R2 R1 3990 BD * LT3970-3.3: R1 = 12.65M, R2 = 7.35M LT3970-3.42: R1 = 12.65M, R2 = 6.93M LT3970-5: R1 = 15.15M, R2 = 4.85M 3970fc 8 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Related Parts
