Datasheet LT3748 (Analog Devices) - 6

LT3748
pin Functions VIN (Pin 1)
Input Voltage. This pin supplies current to the
GND (Pins 8, 9):
Ground. internal start-up circuitry and is the reference voltage for
SS (Pin 10):
Soft-Start Pin. This pin delays start-up and the feedback circuitry connected to the RFB pin. This pin clamps V must be locally bypassed with a capacitor. C pin voltage. Soft-start timing is set by the size of the external capacitor at the pin. Switching starts when
EN/UVLO (Pin 3):
Enable/Undervoltage Lockout. A resistor VSS reaches ~0.65V. divider connected to VIN is tied to this pin to program the
V
minimum input voltage at which the LT3748 will operate.
C (Pin 11):
Compensation Pin for the Internal Error Amplifier. Connect a series RC from this pin to ground to At a voltage below ~0.5V, the part draws less than 1µA compensate the switching regulator. A 100pF capacitor quiescent current. When below 1.223V but above ~0.5V, in parallel helps eliminate noise. the part will draw quiescent current but will not regulate the INTVCC supply or power the gate drive circuitry. Above
TC (Pin 12):
Output Voltage Temperature Compensation. 1.223V, all internal circuitry will start and the SS pin will Connect a resistor to ground to produce a current pro- source 5μA. When EN/UVLO falls below 1.223V, 2.4μA is portional to absolute temperature to be sourced into the sunk from the pin to provide programmable hysteresis RREF node. ITC = 0.55V/RTC. for undervoltage lockout.
RREF (Pin 14):
Input Pin for the External Ground-Referred
INTVCC (Pin 5):
Gate Driver Bias Voltage. This pin supplies Reference Resistor. The resistor at this pin should be 6.04k, current to the internal gate driver circuitry of the LT3748. but for convenience in selecting a resistor divider ratio, The INTVCC pin must be locally bypassed with a capacitor. the value may range from 5.76k to 6.34k.
The resistor
This pin may also be connected to VIN if a third winding
should be as close to the LT3748 as possible
. is not used and if VIN ≤ 20V. If a third winding is used,
R
the INTV
FB (Pin 16):
Input Pin for the External Feedback Resistor. CC voltage should be lower than the input voltage This pin is connected to the transformer primary at the for proper operation. external MOSFET power switch. The ratio of this resistor
GATE (Pin 6):
N-Channel MOSFET Gate Driver Output. to the RREF resistor, times the internal bandgap reference, Switches between INTVCC and GND. determines the output voltage (plus the effect of any non-unity transformer turns ratio). The average current
SENSE (Pin 7):
The Current Sense Input for the Control through this resistor during the flyback period should be Loop. Kelvin connect this pin to the positive terminal of approximately 200μA.
The resistor should be as close
the switch current sense resistor, RSENSE, in the source
to the LT3748 as possible
. of the N-channel MOSFET. The negative terminal of the current sense resistor should be connected to the GND plane close to the IC. 3748fb 6 For more information www.linear.com/LT3748 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 Package Description Typical Application Related Parts