XC6602-03-04

With this N-channel architecture, the regulator can deliver large output currents at very low dropout conditions, for example, V_IN = 1.2V and V_OUT = 1.0V (Fig. 1).

As shown in Fig. 2, conventional LDOs typically use a P-channel MOSFET as the driver transistor. In this configuration, the maximum gate-to-source voltage (V_GS) is limited to the difference between V_IN and V_SS. As V_IN decreases, V_GS also decreases, resulting in higher on-resistance at lower input voltages. Additionally, V_IN cannot drop below the IC’s minimum operating voltage.

In contrast, when using an N-channel MOSFET as the driver transistor (Fig. 3), the maximum V_GS is determined by the difference between V_BIAS and V_OUT. Since V_BIAS is supplied from a higher-level source (e.g., 3V or 5V system), V_GS increases as V_OUT decreases, enabling low on-resistance operation even at reduced voltages.

Fig.1 Typical Application Circuit

Fig.2 P-Ch MOS Driver LDO

Fig.3 N-Ch MOS Driver LDO

By using a bias voltage drive, they maintain low ON resistance even at low output voltages. This design reduces voltage drops caused by load fluctuations and achieves a lower dropout voltage compared to earlier products, ensuring stable output even under high current demand.

The WLP-5-02 package further enhances performance by using metal wiring instead of traditional wire bonding, which lowers ON resistance. As a result, dropout voltage characteristics and Vout-Iout performance are significantly improved over conventional packaging (see Fig. 4, 5).

Dropout Voltage (Fig.4)

XC6602A121xR-G
Ta=25℃,V_BIAS=V_CE=3.6V, C_BIAS=C_IN=1.0μF,C_L=2.2μF

Output Voltage vs.Output Current (Fig.5)

XC6602A121xR-G
Ta=25℃,V_IN=1.5V,V_BIAS=V_CE=3.6V, C_BIAS=C_IN=1.0μF,C_L=2.2μF

The soft-start circuit suppresses inrush current from V_IN to V_OUT at startup, thereby minimising voltage fluctuations on the V_IN line.    In a configuration such as the example in Fig. 3, this prevents the front-end IC’s over-current protection from being triggered by inrush current, allowing controlled sequencing. Even with low on-resistance, the circuit ensures a smooth power-on without negatively impacting other ICs.

For the XC6602 and XC6604 Type A, the soft-start time is internally fixed at 430 μs (typical). In contrast, the XC6603 series allows adjustment of the soft-start time via an external capacitor (C_SS), enabling optimization to suit specific inrush current requirements. 

Fig.6 Soft-start Characteristics (XC6603 Series) CE Rise Transient Response

Fig.7 Soft-start Time vs. Capacitor Capacitance

              Test Condition:  V_BIAS=3.6V, V_IN=1.5 V, V_OUT=1.2 V, V_CE=0V⇒3.6 V(tr=5μs), I_OUT=100mA, C_BIAS=C_IN=1.0μF, C_L=10μF, Ta=25°C