XC9206/XC9207/XC9208
Series
■OPERATIONAL
EXPLANATION (Continued)
< U.V.L.O. Circuit>
When the V
IN
pin voltage becomes 1.4 V or lower, the P-channel output driver transistor is forced OFF to prevent false pulse
output caused by unstable operation of the internal circuitry. When the V
IN
pin voltage becomes 1.8 V or higher, switching
operation takes place. By releasing the U.V.L.O. function, the IC performs the soft start function to initiate output startup
operation. The soft start function operates even when the VIN pin voltage falls momentarily below the U.V.L.O. operating
voltage. The U.V.L.O. circuit does not cause a complete shutdown of the IC, but causes pulse output to be suspended;
therefore, the internal circuitry remains in operation.
< Function of CE/MODE pin >
The XC9206/9207/9208 series will enter into shut down state by inputting a low level signal to the CE/MODE pin. During a
shut down state, the current consumption of the IC becomes 0μA (TYP.), with a state of high impedance at the Lx pin and
V
OUT
pin. The IC starts its operation by inputting a high level signal to the CE/MODE pin. The input of the CE/MODE pin is
a CMOS input and the sink current is 0μA (TYP.).
●XC9206A
/ 07A series - Examples of how to use CE/MODE pin
SW_CE
ON
A
OFF
ON
B
OFF
(A)
(B)
STATUS
Chip Disable
PWM control (XC9206),
PWM/PFM automatic switching control (XC9207)
PWM control (XC9206),
PWM/PFM automatic switching control (XC9207)
Chip Disable
●XC9208A
series - Examples of how to use CE/MODE pin
SW_CE
ON
A
OFF
OFF
ON
(A)
(B)
SW_PMW/PFM
*
ON
OFF
*
ON
OFF
STATUS
Synchronous PWM control
Non-synchronous PWM/PFM
automatic switching control
Chip Disable
Chip Disable
Non-synchronous PWM/PFM
automatic switching control
Synchronous PWM control
B
OFF
OFF
Intermediate voltage can be generated by RM1 and RM2. Please set the value of each R1, R2, RM1, RM2 at around 100kΩ.
For switches, CPU open-drain I/O port and transistor can be used.
< PWM / PFM >
XC9207/9208 series features PWM/PFM automatic switching control.
With the automatic PWM/PFM switching control function, the series ICs are automatically switched from PWM control to
PFM control mode under light load conditions. If during light load conditions the coil current becomes discontinuous and
on-time rate falls lower than PFM duty, the PFM circuit operates to output a pulse with a fixed on-time rate from the Lx pin.
During PFM operation with this fixed on-time rate, pulses are generated at different frequencies according to conditions of
the moment. This causes a reduction in the number of switching operations per unit of time, resulting in efficiency
improvement under light load conditions. However, since pulse output frequency is not constant, consideration should be
given if a noise filter or the like is needed. Necessary conditions for switching to PFM operation depend on input voltage,
load current, coil value and other factors.
8/16
TOREX [ TOREX SEMICONDUCTOR ]
