MB3802 Просмотр технического описания (PDF) - Fujitsu

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Компоненты Описание

производитель

MB3802

Power Management Switch

Fujitsu 

MB3802

s BLOCK DIAGRAM AND EXTERNAL CONNECTIONS

Power supply

CD

Extemal capacitor

DLY

SW IN

SW OUT

Load

GND

Load discharge

circuit

Switch-ON

circuit

DC/DC converter

Switch-OFF

circuit

Comp

V IN

(+)

Switch control

DDG

Note: The MB3802 incorporates two switch blocks as shown above. However, GND is common to both blocks.

s BLOCK DESCRIPTION

The MB3802 is a one-way switching IC with the SWIN and SWOUT pins serving respectively for input and output.

When VIN exceeds 2.2 V, the Comp. starts driving the DC/DC converter to switch the N-ch MOS and applies the

optimum voltage for the switch gate.

The DC/DC converter boosts the VIN voltage.

When VIN is below 2.1 V, the Comp. stops the DC/DC converter, starts the switch-OFF circuit, and discharges

the voltage from the switch gate to GND. The switch-OFF circuit is powered from the SWIN and consumes 0.4µA

at 5 V.

Since the N-ch MOS back gate is connected to GND, switch-OFF reverse current is prevented irrespective of

the High level state between SWIN and SWOUT. Note, however, that turning the VIN pin on/off with 1.5 V or less

applied to the SWIN pin may cause reverse current to flow because the switch-off circuit does not work then.

For the method of compensating for the operation of the switch-off circuit, see section “sAPPLICATIONS 7.Low-

side Switch.”

The load discharge circuit installed between SWOUT and GND is powered by the DCG pin, and discharges the

load-side capacitor at switch OFF. When it is not necessary to discharge the load, connect the DCG pin to GND.

The DLY pins are for connection to an external capacitor to delay the switch-ON/OFF time. The surge current

at the load side is cut at power-on by controlling the switch-ON time. The switch-ON time depends on the boot

time of the DC/DC converter. Consequently, when the VIN level is high and the SWIN level is low, the switch-ON

time is small; when the SWIN level is high, the switch-OFF time is small.

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