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4964B–AUTO–07/07

ATA6842

7.6

5V Linear Regulators

The ATA6842 offers two independent 5V supplies. The main supply (V5) is available only in

active mode while the auxiliary 5V supply (V5A) is active all the time. The ATA6842 activates the

basis of external bipolar transistors via pins B5 and B5A. The currents of the regulators V5

(150 mA) and V5A (30 mA), defined in the datasheet, can only be achieved if the external tran-

sistors fulfil certain requirements in terms of current amplification and transit frequency.

Especially for V12 = 5.8V a low saturation voltage of B5 and B5A in combination with the forward

diode voltage and a low saturation voltage (Uce,sat) of the external bipolar transistors is

required. For fast load changes at V5 a high transit frequency is necessary (typically

f

For voltage monitoring and as references for the voltage regulators two independent bandgaps

are used. The voltage monitoring functions of V5 and V5A generate a reset pulse at RESN and

RESAN if the limits are exceeded (see Table 7-9 on page 25). For internal voltage supply, an

additional linear regulator (VI) is implemented.

7.7

Current Measurement

The ATA6842 contains two differential amplifiers for current measurement. The input signal of

each amplifier is a voltage drop over an external current sense resistor. The amplification,

defined by the ratio of external resistors, provides a reasonable signal for the following A/D con-

verter. The output is limited to V5.

7.8

Relay Driver

The ATA6842 features four current-limited relay drivers for motor direction control relays. The

relays are controlled by an SPI command and the input of the enable relay driver (ERD). Error

conditions disable the relays permanently (see Table 7-9 on page 25).

Note:

The simultaneous activation of the relay drivers RD1 and RD4 or RD2 and RD3 is not possible

(see Table 7-2 and Table 7-3). This feature ensures that if ATA6842 is used in DC motor applica-

tion, the motors can only operate in the same direction.

Table 7-2.

Relay Status Table

TRD1 (SPI)

TRD2 (SPI)

ERD

RD1

RD2

Low

Low

x

Open drain

Open drain

Low

High

High

Open drain

Low

High

Low

High

Low

Open drain

High

High

High

Open drain

Open drain

x

x

Low

Open drain

Open drain

Table 7-3.

Relay Status Table

TRD3 (SPI)

TRD4 (SPI)

ERD

RD3

RD4

Low

Low

x

Open drain

Open drain

Low

High

High

Open drain

Low

High

Low

High

Low

Open drain

High

High

High

Open drain

Open drain

x

x

Low

Open drain

Open drain