XC9206/XC9207/XC9208
Series
■
TYPICAL APPLICATION CIRCUIT
CE/MODE
4
CE/ VOUT
MODE
VSS
3
2
L
1
SD
CL
(ceramic)
VIN
5
CIN
(ceramic)
VIN
Lx
VOUT
(500mA)
●FOSC=1.2MHz
L
: 4.7μH (CDRH3D16,
SUMIDA)
SD : CRS02 (TOSHIBA)
C
IN
: 4.7μF (Ceramic)
C
L
: 10μF (Ceramic)
●FOSC=300kHz
L
: 22μH (CDRH4D18,
SUMIDA)
SD : CRS02 (TOSHIBA)
C
IN
: 4.7μF (Ceramic)
C
L
: 10μF (Ceramic)
●FOSC=600kHz
L
: 10μH
(CDRH4D18C,
SUMIDA)
SD : CRS02 (TOSHIBA)
C
IN
: 4.7μF (Ceramic)
C
L
: 10μF
(Ceramic)
*SD : Schottky diode
* XC9206/9207/9208 series wire connection
■OPERATIONAL
EXPLANATION
Each unit of the XC9206/9207/9208 series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM
comparator, phase compensation circuit, output voltage adjustment resistors, driver transistor, current limiter circuit, U.V.L.O.
circuit and others. The series ICs compare, using the error amplifier, the voltage of the internal voltage reference source with
the feedback voltage from the V
OUT
pin through resistors R1 and R2. Phase compensation is performed on the resulting error
amplifier output, to input a signal to the PWM comparator to determine the turn-on time during PWM operation. The PWM
comparator compares, in terms of voltage level, the signal from the error amplifier with the ramp wave from the ramp wave
circuit, and delivers the resulting output to the buffer driver circuit to cause the Lx pin to output a switching duty cycle. This
process is continuously performed to ensure stable output voltage. The current feedback circuit monitors the P-channel MOS
driver transistor current for each switching operation, and modulates the error amplifier output signal to provide multiple
feedback signals. This enables a stable feedback loop even when a low ESR capacitor, such as a ceramic capacitor, is used,
ensuring stable output voltage.
< Reference Voltage Source >
The reference voltage source provides the reference voltage to ensure stable output voltage of the ICs.
< Ramp Wave Circuit >
The ramp wave circuit determines switching frequency. The frequency is fixed internally and can be selected from 300kHz,
600 kHz and 1.2 MHz. Clock pulses generated in this circuit are used to produce ramp waveforms needed for PWM
operation, and to synchronize all the internal circuits.
< Error Amplifier >
The error amplifier is designed to monitor output voltage. The amplifier compares the reference voltage with the feedback
voltage divided by the internal resistors (R1 and R2). When a voltage lower than the reference voltage is fed back, the output
voltage of the error amplifier increases. The gain and frequency characteristics of the error amplifier output are fixed internally
to deliver an optimized signal to the mixer.
<Current Limit>
The current limiter circuit of the XC9206/9207/9208 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.
①When
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 timing.
②When
the driver transistor is turned off, the limiter circuit is then released from the current limit detection state.
③At
the next pulse, the driver transistor is turned on. However, the transistor is immediately turned off in the case of an over
current state.
④When
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. Once the IC is in suspension mode, operations can be resumed
by either turning the IC off via the CE /MODE pin, or by restoring power to the V
IN
pin. The suspension mode does not mean a
complete shutdown, but a state in which pulse output is suspended; therefore, the internal circuitry remains in operation. The
constant-current type current limit of the XC9206A/9207A/9208A series can be set at 600 mA.
Limit < #ms
Limit< #mS
Limit > #ms
Limit> #mS
Current Limit LEVEL
IOUT
0mA
VOUT
VSS
LX
CE/MODE
Restart
VIN
7/16
TOREX [ TOREX SEMICONDUCTOR ]
