XCM519 datasheet(21/49 Pages) TOREX

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XCM519

Series

■OPERATIONAL EXPLANATION (Continued)

The IC internal circuitry can be shutdown via the signal from the EN2 pin with the XCM519 series. In shutdown mode, output at

the VROUT pin will be pulled down to the VSS level via R1 & R2. However, as for the XCM519 series, the CL auto-discharge

resistor is connected in parallel to R1 and R2 while the power supply is applied to the VIN2 pin. Therefore, time until the VROUT

pin reaches the VSS level becomes short.

The EN2 pin of XCM519 has pull-down circuitry so that EN2 input current increase during IC operation. The EN2 pin of XCM519

does not have pull-down circuitry so that logic is not fixed when the CE pin is open. If the EN2 pin voltage is taken from VBIAS

pin or VSS pin then logic is fixed and the IC will operate normally. However, supply current may increase as a result of through

current in the IC's internal circuitry when medium voltage is input.

■NOTE ON USE

When the DC/DC converter and the VR are connected as VIN1=VBIAS, VDCOUT=VIN2, the following points should be noted.

When the DC/DC load is changed drastically during a light load of the VR, a fluctuation may happen in tenths of mV. This

value can be reduced by increasing CL1 load capacitance at the DC/DC in order to reduce a voltage drop during load

transient.

It is recommended that both CIN1 and CBIAS are connected to each pin separately. When one capacitor is used instead of

the two, this capacitor should be placed in 10μF or more as close as the VIN1 and the PGND (AGND) pins of the DC/DC

circuit. Please ensure it by testing on the actual product design.

It is recommended that both CL1 and CIN2 are connected to each pin separately. When one capacitor is used instead of the

two, this capacitor should be selected in 4.7μF or bigger. Please ensure it by testing on the actual product design.

CL2 of the VR is recommended 4.7μA. When larger value is used in CL2, the larger value is also used in CL1 as in

proportional. Please be noted that when CL2 capacitance of the VR is getting large, an inrush current increases at VR

start-up, DC/DC short circuit protection starts to operate, as a result, the IC may happen to stop.

20μs/div

立ち上がり

立下り

50μs/div

1ch:DC/DC VOUT:50mV/div

2ch:VR VOUT:50mV/div

4ch:VR IOUT:200mA/div

1ch:DC/DC VOUT:50mV/div

2ch:VR VOUT:50mV/div

4ch:VR IOUT:200mA/div

50us/div

EN2(5V/div)

DCOUT(1V/div)

VROUT(1V/div)

IIN2(500mA/div)

* VR inrush current IIN2 makes DC/DC short-circuit protection to

start, as a result, the IC may happen to stop.

The left waver forms are taken at CL1=10μ, CL2=10μF(in

contrast to the recommended 4.7μF).

However, it improves when CL1=20μF.

XCM519 Datasheet(PDF) 21 Page - Torex Semiconductor

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