IC-DC datasheet(15/19 Pages) ICHAUS

15 / 19 page

iC-DC

2-CHANNEL BUCK/BOOST DC/DC CONVERTER

Rev B1, Page 15/19

ERROR EVALUATION

Supply voltage monitor

Supply voltage VBR is monitored. If the normal volt-

age range is overshot or undershot, this is signaled at

open-drain pin VBROK. The bias current generated by

an external reference resistor is also monitored and an

error signaled at VBROK should the permissible range

be exceeded. If an error has occurred, pin VBROK is

switched to GND.

Output voltage monitor

The two linear regulator output voltages VCC1 and

VCC2 are also monitored. If the overvoltage threshold

is overshot or the undervoltage threshold undershot

(e.g. due to overload), a message is generated at the

current-limited push-pull outputs V1OK and V2OK. Volt-

age outputs POE1 and POE2 are shut down.

Output voltage monitor self-test

Using pin TEST the voltage monitoring comparators at

V1OK and V2OK can be tested during ongoing opera-

tion. The undervoltage and overvoltage thresholds of

V1OK and V2OK are checked in turn with each test.

For this purpose, pin TEST is increased to above the

threshold voltage by an external driver. Correct func-

tioning is signaled by low signals at pins V1OK and

V2OK. The function of the connected POE1 and POE2

outputs remains unaffected.

Temperature monitor

The internal chip temperature is monitored. If the

monitor indicates overtemperature, all switches on the

switching converter are shut down. These are auto-

matically re-enabled when the chip temperature has

dropped below the restart temperature. A message

is signaled at open-drain pin TOK for as long as the

converter is shut down due to chip overtemperature.

The protective switch (VB / VBR) has its own over

temperature protection, which is also operative during

standby mode.

As error outputs VBROK and TOK are current limited,

an LED can be directly connected up for visual mes-

sage display. However, the additional power dissipation

this causes in the IC must be taken into account. By

placing resistor RLED in series with the LED, this ad-

ditional chip power loss can be reduced in the event

of error. CMOS or TTL-compatible logic inputs can be

activated by pull-up resistors at VBROK and TOK.

AUTARKY FUNCTION

By inserting a capacitor at VBR, an Autarky function can

be realized should the supply fail at VB. This Autarky

function guarantees the linear regulator output voltages

for some time. If the voltage at VBR is greater than at

VB (elec. char. no. 109), this is signaled by current-lim-

ited open-drain output NAUT. To ensure that VBR > VB

should the supply voltage fail, it is recommended that a

resistor be switched between VB and GND in order to

generate the required differential voltage of dVBR,VB.

With this capacitor acting as a buffer, the effect of cur-

rent spikes feeding back into the supply voltage VB is

also reduced.

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