LT8625SP datasheet(10/44 Pages) AD

10 / 44 page

Data Sheet

LT83401/LT83402

analog.com

Rev. 0

10 of 44

4, 8

VIN

The VIN pins supply current to the LT83401/LT83402 internal circuitry and to the

internal topside power switch. Two 0402 capacitors of 0.1µF or more should be placed

to bypass both VIN pins, with the positive terminal of the input capacitor as close as

possible to the VIN pins, and the negative capacitor terminal as close as possible to the

GND pins. VIN pins must also be connected with an additional local bypass capacitor of

4.7µF or more. To provide sufficient headroom for the current reference, VIN must be at

least 900mV higher than the required regulation setpoint that is programmed via the

SET pin. For example, for the required regulation setpoint of 3.3V, VIN must be at least

3.3V + 900mV = 4.2V, or higher.

5, 7, 16

(Exposed

Pad)

GND

Ground. Place the negative terminal of the input capacitor as close to the GND pins as

possible. The exposed pads should be soldered to the PCB for good thermal

performance. If necessary due to manufacturing limitations, the exposed pad may be

left disconnected; however, the performance degrades.

The SW pin is the output of the internal power switches. Connect this pin to the

inductor. This node must be kept small on the PCB for good performance and low EMI.

BST

This pin is used to provide a drive voltage higher than the input voltage to the topside

power switch. Place a 0.1µF boost capacitor as close as possible to the IC.

INTVCC

Internal 3.4V Regulator Bypass Pin. The internal power drivers and control circuits are

current is supplied by VIN. Decouple this pin to ground with at least 1µF low equivalent

series resistance (ESR) ceramic capacitor placed close to the IC.

EN/UVLO

A voltage at this pin greater than 0.75V enables switching, and a voltage less than

200mV is guaranteed to shut down the internal current bias and sub-regulators. The

hysteretic threshold voltage is 0.75V going up and 0.7V going down. Connect to VIN if

the shutdown feature is not used. An external resistor divider from VIN is used to

program a VIN threshold below which the LT83401/LT83402 shuts down.

The VC pin is the output of the internal error amplifier. The voltage on this pin controls

the peak switch current. Connect an RC network from this pin to ground to

compensate the control loop.

SET

This pin is the non-inverting input of the error amplifier and the regulation setpoint for

the LT83401/LT83402. SET sources a precision 100μA current that flows through an

external resistor connected between the SET and GND. The LT83401/LT83402’s output

voltage is determined by VSET = ISET × RSET when used in the default unity gain

configuration. SET pin voltage range is from 0 to 15V. For applications with output

voltages above 15V, see the Output Voltages Above 15V section. A capacitor should be

added from SET to GND for the best noise performance. Increasing this capacitance

further improves noise at the expense of increased start-up time. See the SET Pin

Capacitor: Noise and Soft-Start section for important information on how to select this

capacitor. For optimum load regulation, Kelvin connect the ground side of the SET pin

resistor directly to the load. This pin is pulled to ground with a 520Ω MOSFET (RSET–

PULLDOWN) during shutdown and fault conditions.

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