L4938ED, L4938EPD

Application information

Doc ID 17243 Rev 2

11/20

3

Application information

Figure 3.

Application diagram

1.

The leakage of CT must be less than 0.5 mA (2 V). If an external resistor between CT and VOUT1 is applied,

the leakage current may be increased. The external resistor should have more than 30 K

Ω.

For stability: Cs

≥ 1 µF, C01 ≥ 10 µF, C02 ≥ 10 µF, ESR ≤ 5Ω (designed target).

2.

For transients exceeding 20 V or -20 V external protection is required at the pins SI and EN as shown at

pin EN. The protection proposed provides proper function for transients in the range of ±200 V. If the zener

diode is omitted the external resistor should be raised to 200 K

Ω to limit the current to 1 mA. Without the

zener diode, the function 20 V or -20 V can not be guaranteed.

3.1

Functional description

The L4938ED and L4938EPD are monolithic integrated dual voltage regulators, based on

the STM modulator voltage regulator approach. Several outstanding features and auxiliary

functions are implemented to meet the requirements of supplying microprocessor systems

in automotive applications. Nevertheless, it is suitable also in other applications where two

stabilized voltages are required. The modular approach of this device allows to get easy

also other features and functions when required.

3.2

Standby regulator

The standby regulator uses an isolated collector vertical PNP transistor as a regulating

element. With this structure very low dropout voltage at currents up to 100 mA is obtained.

The dropout operation of the standby regulator is maintained down to 3 V input supply

voltage. The output voltage is regulated up to the transient input supply voltage of 40 V. With

this feature no functional interruption due to overvoltage pulses is generated.

(See note 1)

(See note 2)