XC9519 TOREX [Torex Semiconductor], XC9519 Datasheet - Page 10

• Manufacturer Part Number: XC9519
• Description: Dual Output Step-Up/Inverting DC/DC Converter
• Manufacturer: TOREX [Torex Semiconductor]

■OPERATIONAL EXPLANATION (Continued)
<Reference Voltage Source>
<Step-up DC/DC Converter Error Amplifier>
voltage. When a voltage lower than the reference voltage is feedback to the FBP pin voltage, the output voltage of the error amplifier goes high.
External compensation of the error amplifier frequency characteristic is also possible.
<Inverting DC/DC Converter Error Amplifier>
voltage higher than GND is feedback to the FBN pin voltage, the output voltage of the error amplifier goes high. External compensation of the
error amplifier frequency characteristic is also possible.
<Ramp Wave Circuit>
used to produce ramp waveforms needed for PWM operation, and to synchronize all the internal circuits.
<UVLO Circuit>
operation of the internal circuitry. When the AVIN pin voltage becomes 2.4V or higher, switching operation takes place. By releasing the UVLO
function, the IC performs the soft start function to initiate output startup operation. The soft start function operates even when the AVIN pin
voltage falls momentarily below the UVLO detect voltage. The UVLO circuit does not cause a complete shutdown of the IC, but causes pulse
output to be suspended; therefore, the internal circuitry remains in operation.
<Thermal Shutdown>
operating and the driver transistor will be turned off when the chip’s temperature reaches 150
after shutting of the current flow, the IC performs the soft start function to initiate output startup operation.
<PFM Switch Current>
(t
t
< PFM Duty Limit >
(e.g. the condition that the step-up ratio is large), it’s possible for the driver transistor to be turned off even when the coil current doesn’t reach to I
(I
10/38
ON
In PFM control operation, the maximum duty cycle (DTY
ON
PFMN
The inverting DC/DC converter error amplifier is an amplifier for output voltage monitoring. The FBN pin voltage is compared to GND. When a
The reference voltage source provides the reference voltage to ensure stable output voltage of the DC/DC converter.
The step-up DC/DC converter error amplifier is an amplifier for output voltage monitoring. The FBP pin voltage is compared to the reference
The ramp wave circuit determines switching frequency. The frequency is fixed 1.2MHz internally. Clock pulses generated in this circuit are
When the AVIN pin voltage becomes 2.2V or lower, the driver transistor is forced OFF to prevent false pulse output caused by unstable
For protection against heat damage of the ICs, thermal shutdown function monitors chip temperature. The thermal shutdown circuit starts
In PFM control operation, until coil current reaches to a specified level (I
= L ×I
) that the driver transistor is kept on can be given by the following formula.
XC9519
).
PFMP
(I
PFMN
) / V
IN
Series
LIMIT_PFM
) is set to 50% (TYP.). Therefore, under the condition that the duty increases
PFMP
, I
PFMN
), the IC keeps the driver transistor on. In this case, time
o
C. When the temperature drops to 130
o
C or less
PFMP