XC9223/9224 Series
1A Driver Transistor Built-In Step-Down DC/DC Converters
Preliminary
OPERATIONAL EXPLANATION (Continued)
<Current Limit>
The current limiter circuit of the XC9223/9224 series monitors the current flowing through the P-channel MOS driver transistor connected to the Lx pin, and
features a combination of the constant-current type current limit mode and the operation suspension mode. For the current limit values, please select the
values either from 1.5A (MIN.) when the LIM pin is high level or 0.5A (MIN.) when the LIM pin is low level.
1
When the driver current is greater than a specific level, the constant-current type current limit function operates to turn off the pulses from the Lx pin at
any given time.
2
When the driver transistor is turned off, the limiter circuit is then released from the current limit detection state.
3
At the next pulse, the driver transistor is turned on. However, the transistor is immediately turned off in the case of an over current state.
4
When the over current state is eliminated, the IC resumes its normal operation.
The IC waits for the over current state to end by repeating the steps
1
through
3
. If an over current state continues for several msec and the above three
steps are repeatedly performed, the IC performs the function of latching the OFF state of the driver transistor, and goes into operation suspension mode.
After being put into suspension mode, the IC can resume operation by turning itself off once and then starting it up using the CE pin, or by restoring power to
the VIN pin. Integral latch time may be released from a current limit detection state because of the noise. Depending on the state of a substrate, it may
result in the case where the latch time may become longer or the operation may not be latched. Please locate an input capacitor as close as possible.
Limit < # mS
Limit > # mS
Current Limit LEVEL
IDOUT
0mA
DCOUT
VSS
LX
CE
Restart
VIN
<Thermal Shutdown>
For protection against heat damage of the ICs, thermal shutdown function monitors chip temperature. The XC9223/9224 series build in three protection
functions: integral latch protection, thermal shutdown, and short-circuit protection. The thermal shutdown circuit starts operating and the driver transistor
O
O
will be turned off when the chip’s temperature reaches 150 C. When the temperature drops to 130 C or less after shutting of the current flow, the IC
performs the soft start function to initiate output startup operation.
<Short-Circuit Protection>
The short-circuit protection circuit monitors FB voltage. In case where output is accidentally shorted to the Ground and when the FB voltage decreases less
than half of the FB voltage, the short-circuit protection operates to turn off the driver transistor. In suspension mode, the operation can be resumed by
either turning the IC off and on via the CE/MODE pin, or by restoring power supply to the VIN pin.
<Voltage Detector>
The detector block of the XC9223/9224 series detects a signal inputted from the VDIN pin by the VDOUT pin.
<U.V.L.O. Circuit>
When the VIN pin voltage becomes 1.4V 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 VIN pin voltage becomes 1.8V 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.
<MODE/SYNC>
A MODE/SYNC pin has two functions, a MODE switch and an input of external clock signal. The MODE/SYNC pin operates as the PWM mode when
applying high level of direct current and the PFM/PWM automatic switching mode by applying low level of direct current, which is the same function as the
normal MODE pin.
internal clock signal.
By applying the external clock signal (±25% of the internal clock signal, ON Duty 25% to 75%), the MODE/SYNC pin switches to the
Also the circuit will synchronize with the falling edge of external clock signal. While synchronizing with the external clock signal, the
If the MODE/SYNC pin holds high or low level of the external clock signal for several
µS,
the
MODE/SYNC pin becomes the PWM mode automatically.
MODE/SYNC pin stops synchronizing with the external clock and switches to the internal clock operation.
Data Sheet
7
DC000019
TOREX [ TOREX SEMICONDUCTOR ]
