EM6156 datasheet(8/11 Pages) EMMICRO

8 / 11 page

EM6156

06/07 – rev.A

www.emmicroelectronic.com

Typical Operating Characteristics

(Typical values are at TA = +25°C unless otherwise noted. WDI, RESET and RESET open)

100

125

150

175

200

225

250

-50 -25

100 125

[ °C ]

[ ns ]

Fig. 11

Watchdog Input Pulse Width tWP vs. Temperature

Functional Description

WDI

RESET

t > t

t < t

POR

High Impedance

POR

Fig. 12

VOUT Monitoring

A microprocessor (μP) reset input starts the microcontroller

in a known state. The EM6156 microcontroller supervisory

circuits assert a reset to prevent code-execution errors

during power-up, power down, and brownout conditions.

RESET

is guaranteed to be a logic low for VDD down to

0.9V. Once VDD exceeds the reset threshold, an internal

timer keeps RESET low for the specified reset timeout

period (tPOR); after this interval, RESET returns high.

If a brownout condition occurs (VDD dips below the reset

threshold), RESET goes low. Each time RESET is asserted

it stays low for the reset timeout period. Any time VDD

goes below the reset threshold the internal timer restarts.

RESET

is the inverse of RESET.

Voltage Regulator

The EM6156 has a 5 V, 150 mA, low dropout voltage

regulator. The low supply current makes the EM6156

particularly suitable for automotive systems which remain

continuously powered. The input voltage range is 2.3 V to

40 V for operation and the input protection includes both

reverse battery (42 V below ground) and load dump

(positive transients up to 45 V). There is no reverse current

flow from the VOUT to the VIN when the VIN equals VSS.

This feature is important for systems which need to

implement (with capacitance) a minimum power supply

hold-up time in the event of power failure. To achieve good

load regulation a 22 μF capacitor (or greater) is needed on

the VIN (see Fig. 17). Tantalum or aluminium electrolytic

are adequate for the 22 μF capacitor; film types will work

but are relatively expensive. Many aluminium electrolytic

have electrolytes that freeze at about –30°C, so tantalums

are recommended for operation below –25°C. The

important parameters of the 22 μF capacitor are an

effective series resistance of lower than 4

Ω and a resonant

frequency above 500 kHz.

A output 10 μF capacitor (or greater) and a 100 nF

capacitor are required on the output to prevent oscillations

due to instability. The specification of this 10 μF capacitor

is as per the 22 μF capacitor on the input (see previous

paragraph).

The EM6156 will remain stable and in regulation with no

external load and the dropout voltage is typically constant

as the input voltage fall below its minimum level (see Table

2). These features are especially important in CMOS RAM

keep-alive applications.

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