
11/53
XC9504
Series
NOTES ON USE (Continued)
Hint on application 
1. Channel 1 (Step-Up) How to shut down the output voltage during standby mode 
If the circuit configuration shown as an example of typical application circuits is used, voltage V
IN
 will occur at V
OUT1
 when 
the IC is in standby, the diode being bypassed.  This can cause circuits connected to V
OUT1
 to malfunction.
> Example of typical application circuit 1: 
VOUT1
MOSFET1
Set R1 so as to prevent leakage current of N-ch MOSFET 2. 
> Example of typical application circuit 2: Power Ready Function 
The combination of R 2, C 1, and the threshold 
voltage of approximately 0.7 V of NPN Bip 1 is 
used to produce a delay time between the 
circuits being enabled and P-ch MOSFET 1 
being switched on.  Delay time set to 20ms 
ensures power to be made ready in a favorable 
manner, as soft start of this product is 
completed during the delay time. 
Set Value (Example) 
VOLTAGE (V)
2.5 
3.3 
5.0 
R2 (k
Ω
) 
430 
470 
430 
C1 (
μ
F) 
0.15 
0.18 
0.33 
Time to make power ready is calculated by the equation below. 
Time = - R2 x C1 x Ln (1 - 0.7 / [ON / OFF Signal Voltage ] 
Set R1 so as to prevent leakage current of NPN (Bip 1). 
N-ch MOSFET 2 and the inverter enables power to be turned off quickly.
2. Channel 2 (Inverting): Soft start circuit 
Channel 2 (inverting) is subject to the overshoot of output voltage 2 (V
OUT2
) at start-up.  It is possible to control the 
overshoot of output voltage 2 (V
OUT2
), 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 (V
OUT1
) of channel 1 increase gently as soft start, thereby controlling the overshoot.
> Example of typical application circuit: Improved Soft start 
This example is effective when EN 1 and EN 2 are enabled with different timings under light load condition (the coil current 
being discontinuous).  
SBD1
FB1
EN1
Pch
Inside of
XC9504 IC
RFB11
RFB12
CL1
CFB1
Nch
MOSFET2
ON/OFF
signal
R1
VOUT1
SBD1
FB1
EN1
Pch
MOSFET1
RFB11
RFB12
CFB1
CL1
R1
R2
C1
NPN
Bip1
Nch
MOSFET2
Inside of
XC9504 IC
ON/OFF
signal
SBD2
VOUT1
FB2
Inside of
XC9504 IC
RFB21
CFB21
VOUT2
CL2
RFB22
EN2
ON/OFF
signal
Pch
MOSFET1
R1
Nch
MOSFET2
Time to make soft start time is calculated by the equation below.   
Time
ss2
 = -R
FB21
 C
FB2
1 / Ln  1 –  
Example) 
When 
V
OUT1
 = 15V and V
OUT2
 = - 7.5V,
R
FB21
 = 59.6k
, R
FB22
 = 100k
 by the equation below. 
V
OUT2
 = (0.9 - V
OUT1
) x (R
FB21
 / R
FB22
) + 0.9 
When the light load, C
FB21
=0.1
F or lower value can be used. 
Therefore, when C
FB21
=0.027
F, 
Time_ss2 = 5.0ms and V
OUT2
 = 95% of setting value 
(0.9-V
OUT2
)
(V
OUT1
 – 0.9)
R
FB22
)  
R
FB21
)
3. Channel 2 (Inverting): Withstand voltage of transistor 
The voltage applied between the drain and source is the sum of V
IN
 and V
OUT2
.  Select a transistor with an absolute V
DSS
rating that is suitable for your operating conditions. Example: The voltage applied across V
DS
 of a transistor will be 20.0V if 
V
IN
 = 5.0 V and V
OUT2
 = -15.0 V. Under this condition, a transistor with V
DSS
 higher than 20.0V should be selected.  (Use 
a transistor with V
DSS
 that is 1.5 times the applied voltage or more, as a standard.)