XC6419 Datasheet, PDF (8/29 Pages) Torex Semiconductor – Dual LDO Regulator (ch1=300mA, ch2=100mA) with ON/OFF Switch

XC6419 Series
ç˙_{OPERATIONAL DESCRIPTION}
The voltage divided by resistors Rx1 and Rx2 is compared with the internal reference voltage by the error amplifier. The
P-channel MOSFET connected to the VOUT pin is then driven by the subsequent output signal. The output voltage at the
VOUT pin is controlled and stabilized by a system of negative feedback. The current limit circuit and short protect circuit
operate in relation to the level of output current. Further, the IC's internal circuitry can be shutdown via the EN pin's signal.
<CL Auto-Discharge Function>
XC6419xB/Bx/xD/Dx series can quickly discharge the electric charge at the output capacitor (CL) through the N-channel
transistor located between the VOUT pin and the VSS pin (refer to the BLOCK DIAGRAM) when a low level signal is applied
to the EN pin. The C_L discharge resistance is set to 550Њ when V_IN is 6.0V (TYP.) and V_OUT is 4.0V (TYP.). Moreover,
discharge time of the output capacitor (CL) is set by the C_L auto-discharge resistance (R) and the output capacitor (CL). By
setting time constant of a CL auto-discharge resistance value [R] and an output capacitor value (CL) as Н(Н=C x R), the
output voltage after discharge via the N channel transistor is calculated by the following formulae.
V = VOUT x e ^–t/Н, or ｔ = τln（VOUT (E) / V）
where
V: Output voltage after discharge, VOUT (E): Output voltage, t: Discharge time,
Н: CL auto-discharge resistance R_DCHGʷCL capacitance C
C_L high-speed discharge function can be set by each regulator.
<Current Limiter, Short-Circuit Protection>
The XC6419 series includes a fold-back circuit, which aid the operations of the current limiter and circuit protection. When
the load current reaches the current limit level, the fold-back circuit operates and output voltage drops. As a result of this
drop in output voltage, output current also decreases. When the output pin is shorted, the output current flows go down to
30mA / ch1 and 15mA/ch2 （TYP.）.
<EN Pin>
Each regulator can be shut-downed via the signal from the EN pin with the XC6419 series. In shutdown mode, output at
the VOUT pin will be pulled down to the VSS level via Rx1 & Rx2. However, as for the XC6419xB/Bx/xD/Dx series, the CL
auto-discharge resistor is connected in parallel to Rx1 and Rx2 while the power supply is applied to the VIN pin.
Therefore, time until the VOUT pin reaches the VSS level becomes short. The output voltage becomes unstable, when the
EN pin is open. If this IC is used with the correct output voltage for the EN pin, the 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
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