XC9106_1 TOREX [Torex Semiconductor], XC9106_1 Datasheet - Page 6

• Manufacturer Part Number: XC9106_1
• Description: PWM Control,PWM/PFM Switching Control, Step-Up DC/DC Converters, Externally Applied Vref
• Manufacturer: TOREX [Torex Semiconductor]

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■OPERATIONAL EXPLANATION
<Error Amp.>
Error amplifier is designed to monitor the output voltage, comparing the feedback voltage (FB) with the reference voltage
Vref. In response to feedback of a voltage lower than the reference voltage Vref, the output voltage of the error amp.
decreases.
<OSC Generator>
This circuit generates the internal reference clock.
<Ramp Wave Generator>
The ramp wave generator generates a saw-tooth waveform based on outputs from the OSC generator.
<PWM Comparator>
The PWM comparator compares outputs from the error amp. and saw-tooth waveform. When the voltage from the Error
amp's output is low, the external switch will be set to ON.
<PWM / PFM Controller>
This circuit generates PFM pulses.
The PWM/PFM automatic switching mode switches between PWM and PFM automatically depending on the load.
PWM/PFM control turns into PFM control when threshold voltage becomes lower than voltage of error amps. Noise is easily
reduced with PWM control since the switching frequency is fixed. Because of the function, control suited to the application
can easily be selected. The series suitable for noise sensitive portable audio equipment as PWM control can suppress noise
during operation and PWM/PFM switching control can reduce consumption current during light loads in stand-by.
<Vref 1 with Soft Start>
The reference voltage of the XC9106/9107 series is adjusted and fixed by external applied voltage. (For output voltage
settings, please refer to the output voltage setting.)
To protect against inrush current, when the power is switched on, and also to protect against voltage overshoot, soft-start time
is set internally to 10ms. It should be noted, however, that this circuit does not protect the load capacitor (C
current. With the Vref voltage limited, and depending upon the input to error amp, the operation maintains a balance between
the two inputs of error amps and controls the EXT pin's ON time so that it doesn't increase more than is necessary.
The XC9106/9107 series alters soft start times by the setting value of reference voltage in order to protect against voltage
overshoot and also to protect against inrush current. Please determine soft start time by the formula equation.
<Enable Function>
This function controls the operation and shutdown of the IC. When the voltage of the CE pin drops to 0.2V or less, disable
mode will be entered, the IC's operations will stop and the EXT pin will be kept at a low level (the external N-ch MOSFET will
be OFF). When the IC is in a state of chip disable, current consumption will be no more than 1.0μA.
When the CE pin's voltage rises to 0.65V or more, enable mode will be entered and operations will recommence. The CE pin
also doubles with reference voltage in the XC9106/9107 series, and the range of reference voltage can be varied externally
from 0.8V to 2.5V.
The XC9106 / 07 series are reference voltage (Vref) apply external step-up DC/DC controller ICs. Output voltage will be set
with external resistors (R
suited to software applications that need to vary voltage such as LCD power supply for PDA.
XC9106/XC9107
T
[Example Computation]
SS
= 8.65
Vref = 0.9V, T
×
Vref + 2.21
FB1
SS
and R
= 8.65
FB2
×
) and Vref value. The series make it easy to control output voltage externally and are
0.9 + 2.21 = 10.0 ms
Series
30
25
20
15
10
5
0
0.0
0.5
XC9106 / XC9107D xxx MR
Reference Voltage Vref (V)
1.0
1.5
2.0
L
) from inrush
2.5
3.0