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XC9128/XC9129 Series
■NOTE ON USE
<Thermal Shutdown>
For protection against heat damage, the thermal shutdown function monitors chip temperature. When the chip’s
temperature reaches 150
O
C (TYP.), the thermal shutdown circuit starts operating and the driver transistor will be turned off.
At the same time, the output voltage decreases. When the temperature drops to 130
O
C (TYP.) after shutting off the current
flow, the IC performs the soft start function to initiate output startup operation.
<MODE>
The MODE pin operates in PWM mode by applying a high level voltage and in PFM/PWM automatic switching mode by
applying a low level voltage.
<Shut-Down>
The IC enters chip disable state by applying low level voltage to the EN pin. At this time, the P-ch synchronous switching
transistor turns on when V
IN>VOUT and vise versa the transistor turns off when VIN<VOUT.
<Adaptor Enable>
While the XC9128 series using step-up DC/DC converters in parallel with an added power source such as AC adaptors, the
circuit needs the step-up DC/DC converter to be transient-efficient for sustaining output voltage in case the added power source
runs down. The AEN/ pin voltage determines whether the added power source is supplied or not so that high-speed following
operation is possible. The IC starts operating although the driver transistor is off when a high level voltage is applied to the
AEN/ pin after a high level voltage is also applied to the EN pin. If the AEN/ pin voltage changes from high level to low level
while the EN pin sustains a high level voltage, the step-up operation starts with high-speed following mode (without soft-start).
The XC9129 series does not have adaptor enable function.
<Error Flag >
For the XC9128 series, the FO pin becomes high impedance during over current state, over temperature state, soft-start period,
and shut-down period.
The XC9129 series does not have flag out function.
■OPERATIONAL EXPLANATION (Continued)
1. Please do not exceed the stated absolute maximum ratings values.
2. The DC/DC converter / controller IC's performance is greatly influenced by not only the ICs' characteristics, but also by
those of the external components. Care must be taken when selecting the external components.
3. Make sure that the PCB GND traces are as thick as possible, as variations in ground potential caused by high ground
currents at the time of switching may result in instability of the IC.
4. Please mount each external component as close to the IC as possible and use thick, short traces to reduce the circuit
impedance.
5. When the device is used in high step-up ratio, the current limit function may not work during excessive load current. In this
case, the maximum duty cycle limits maximum current.
6. When the adaptor enable function is used in the below circuit, please use a diode with low reverse bias current. The sum of
R
AEN1
’s and R
AEN2
’s resistance should be set to manage the reverse bias current.
