Notes on how to use

Hint on application

1. Channel 2 ( Inverting )

Soft start circuit

> Example of typical application circuit : Improved Soft start

Time to make soft start time is calculated by the equation below.

Example )

When VOUT1 = 3.3V and VOUT2 = - 7.5V,

RFB21 = 350k

Ω, RFB22 = 100kΩ by the equation below.

VOUT2 = (0.9 - VOUT1) x (RFB21 / RFB22) + 0.9

When the light load, CFB21=0.1

µF or lower value can be used.

Therefore, when CFB21=0.027

µF,

Time_ss2 = 5.0mS and VOUT2 = 95% of setting value

2. Channel 2 (Inverting)

Withstand voltage of transistor

The voltage applied between the drain and source is the sum of VIN and VOUT 2.

Select a transistor with an absolute VDSS rating that is suitable for your operating conditions.

Example: The voltage applied across VDS of a transistor will be 20.0V if VIN = 5.0 V and VOUT 2 = -15.0 V.

This example is effective when EN 1 and EN 2 are enabled with different timings under light load condition (the coil current being

discontinuous).

Under this condition, a transistor with VDSS higher than 20.0V should be selected. (Use a transistor with VDSS

that is 1.5 times the applied voltage or more, as a standard.)

Channel 2 (inverting) is subject to the overshoot of output voltage 2 (VOUT 2) at start-up. It is possible to control the overshoot of

output voltage 2 (VOUT 2), as shown by circuit example 1 in “Output Voltage Settings for Channel 2” in “Function Settings.”

  In this

circuit configuration, EN 1 and EN 2 are enabled (set to “H” level) simultaneously. This lets output voltage 1 (VOUT 1) of channel 1

increase gently as soft start, thereby controlling the overshoot.

XC9505 Series

2ch. Step-Down / Inverting DC/DC Controller ICs

SBD2

VOUT1

FB2

Inside of

XC9505 IC

RFB21

CFB21

VOUT2

CL2

RFB22

EN2

ON/OFF

signal

Pch

MOSFET1

R1

Nch

MOSFET2

1 -

10