UC1834

UC2834

UC3834

Both the current sense and error amplifiers on the UC1834

are transconductance type amplifiers. As a result, their volt-

age gain is a direct function of the load impedance at their

shared output pin, Pin 14. Their small signal voltage gain as

a function of load and frequency is nominally given by;

=

(f)

700

Ω

=

(f)

70

Ω

for: f

Where:

The UC1834 fault delay circuitry prevents the fault outputs

from responding to transient fault conditions. The delay reset

latch insures that the full, user defined, delay passes before an

over-voltage fault response occurs. This prevents unnecessary

crowbar, or latched-off conditions, from occurring following

sharp under-voltage to over-voltage transients.

The crowbar output on the UC1834 is activated following a

sustained over-voltage condition. The crowbar output remains

high as long as the fault condition persists, or, as long as the

over-voltage latch is set. The latch is set with an over-voltage

fault if the voltage at Pin 15 is above the latch reset threshold,

typically 0.4V. When the latch is set, its Q

− output will pull Pin

15 low through a series diode. As long as a nominal pull-up

load exists, the series diode prevents Q

− from pulling Pin 15

below the reset threshold. However, Pin 15 is pulled low

enough to disable the driver outputs if Pins 15 and 14 are

tied together. With Pin 15 and 14 common, the regulator

will latch off in response to an over-voltage fault. If the

fault condition is cleared and Pins 14 and 15 are momen-

tarily pulled below the latch reset threshold, the driver out-

puts are re-enabled.

APPLICATION INFORMATION

Foldback Current Limiting

5