Datasheet LT8495 (Analog Devices) - 9

LT8495
PIN FUNCTIONS (QFN/TSSOP) SS (Pin 1/Pin 8):
Soft-Start Pin. Place a soft-start capacitor
WDI (Pin 9/Pin 16):
Watchdog Timer Input Pin. This pin on this pin. Upon start-up, the SS pin will be charged by receives the watchdog signal from a microcontroller. If a (nominally) 256k resistor to about 2.1V. the appropriate signal is not received, WDO will pulse low
RT (Pin 2/Pin 10):
Oscillator Frequency Set Pin. Place a for a period equal to the reset delay timer period (tRST). resistor from this pin to ground to set the internal oscil-
VIN (Pin 10/Pin 18):
Supply Input Pin. This pin is typically lator frequency. Minimize capacitance on this pin. See the connected to the input of the DC/DC converter. Must be Applications Information section for more details. locally bypassed.
GND (Pins 3, 4, 11, 13, 14, 15, Exposed Pad 21/Pin 14, SW (Pin 12/Pin 20):
Switch Pin. This is the collector of
Exposed Pad 21):
Ground. Solder all pins and the exposed the internal NPN power switch. Minimize trace area con- pad directly to the local ground plane. The exposed pad nected to this pin to minimize EMI. metal of the package provides both electrical contact to
BIAS (Pin 16/Pin 1):
Supply Input Pin. This pin is typi- ground and good thermal contact to the printed circuit cally connected to the output of the DC/DC converter in board. cases where VIN can be higher than VOUT. Must be locally
NC (Pins 4, 9, 17, 19, TSSOP only):
No Connects: These bypassed. pins are not connected to internal circuitry and must be
FB (Pin 17/Pins 2, 3):
Output Voltage Feedback Pin. The left floating to ensure fault tolerance. LT8495 regulates the FB pin to 1.202V. Connect a resis-
RSTIN (Pin 5/Pin 11):
Reset Input Reference. Connect tor divider between the output, FB and GND to set the a resistor divider to RSTIN to set the threshold voltage regulated output voltage. for asserting RST. The RSTIN voltage is compared to an
CPOR (Pin 18/Pin 5):
WDO and RST Active Delay Period internal 1.1V reference. RSTIN voltages lower than the Programming Pin. Attach an external capacitor (C reference cause RST to assert low. POR) to GND to set the period (tRST). See the Applications Infor-
SWEN (Pin 6/Pin 12):
Switch Enable Detect Pin. This pin mation section for more information. enables/disables the switching regulator and soft-start. A
CWDT (Pin 19/Pin 6):
Watchdog Timer Programming Pin. resistor divider can be connected to SWEN to perform an Place a capacitor (C undervoltage lockout function. WDT) between this pin and ground to adjust the watchdog timer upper (tWDU) and lower (tWDL)
WDE (Pin 7/Pin 13):
Watchdog Timer Enable Pin. Drive boundary periods. See the Applications Information section above 1.1V to enable the watchdog timer function. When for more information. WDE is low, the WDO output driver is disabled causing
RST (Pin 20/Pin 7):
Active Low, Open-Drain Reset. Asserts the pin to be high impedance. low when RSTIN is less than ~1.1V (see Electrical Charac-
WDO (Pin 8/Pin 15):
Watchdog Out. Active low, open- teristics). After RSTIN rises, RST will remain asserted low drain output. WDO asserts low if WDE is enabled and the for the period (tRST) set by the capacitor on the CPOR pin. microcontroller fails to drive the WDI pin of the LT8495 with the appropriate signal. 8495fb For more information www.linear.com/LT8495 9 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Timing Diagrams Operation Applications Information Typical Applications Package Description Revision History Typical Applications Related Parts