PAD123 Thaler Corporation, PAD123 Datasheet - Page 4

• Manufacturer Part Number: PAD123
• Description: Current Limit Accessory Module
• Manufacturer: Thaler Corporation

CURRENT LIMIT ACCESSORY MODULE
The sense voltage inputs of the PAD123 (+IL, -IL, ISC) float
with the output of the host amplifier (PAD119, for example)
and can swing within 5V of either supply rail
The output (OUT, pin 2) is set to trip (go low) when:
Where IS represents +IL and -IL tied together for normal
operation. +IL and -IL can be separated for fold-over current
limiting. For fold-over current limit operation OUT is set to trip
when:
changed by the user. In all cases the circuit is tripped when:
where Io is the output current and Rs is the current limit sense
resistor value.
The output (OUT, pin 2) is an open collector circuit and is
intended to be tied to the host amplifier SD input. The SD
input of the host amplifier has an internal pull-up circuit so if
OUT is used without the host amplifier an external 10k pull-up
resistor will be required.
STATUS, pin 4, is the output that alerts external circuitry that
the current set point has been exceeded and goes high (5V
logic) when this occurs. In various modes of operation
STATUS is connected to the shutdown input (SD) and/or
RESET. See “Applications Circuits” for illustrations on how to
use the several modes of operation.
The SD (shutdown) and RESET inputs can be operated from
system logic signals as required. These are 5V logic inputs. If
not used these inputs are required to be tied to ground or pulled
down by 10kΩ. If these inputs are operated from an open
collector circuit an external pull-up resistor is required. Do not
confuse the SD input of the PAD123 with the SD input of the
host amplifier.
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This 150mV reference is generated internally and cannot be
COMMON MODE RANGE
SD AND RESET INPUTS
SENSE VOLTAGE
STATUS OUTPUT
(+IL)-ISC> 150mV
ISC-(-IL) > 150mV
IS-ISC > 150mV
ISC-IS > 150mV
Io > 150mV/Rs
OUTPUT
or
or
It is possible to operate the PAD123 in several modes
without the need for any external logic circuits by using a
few external passive components. For each of the operating
modes see Figure 3 in “Application Circuits”.
In Mode 1 (Figure 3a) the STATUS output is tied directly to
SD. When the output current of the host amplifier exceeds
the trip point, OUT immediately goes low and latches off
the output stage of the host amplifier. To restart the host
amplifier a “high” on the RESET pin is required.
In Mode 2 (Figure 3b) the STATUS output is tied to the SD
input through a RC circuit (R1, C1). The RC circuit
provides a time delay. This is useful when, for example, it is
known that the host amplifier output current will exceed the
set point current for a short time and still not exceed the
SOA of the amplifier. This might occur when starting a
motor, for example. The time delay can be calculated by:
Where T is the time delay, R is the resistance in ohms and C
is the capacitance in farads. The minimum resistor value
is 100kΩ.
In Mode 3 (Figure 3c) an auto-reset can be applied by
adding R2, C2 to the RESET input. This time delay must be
greater than R1, C1 but operates in the same way and is
calculated in the same way. Mode 3 can be used with Mode
1 if desired.
Note that any unused input pins must be grounded (pins
1 or 3).
Connections for the PAD123 are incorporated into the
printed circuit boards included with evaluation kits for
compatible amplifier models. Either standard or fold-over
current limit can be implemented. Bread-boarding pads are
provided to connect the PAD123 in any of the operating
modes discussed above.
spreadsheet available on the Thaler website that will assist
in calculating values needed to implement the fold-over
current limit as well as analyzing many other design issues.
OPERATING MODES
EVALUATION KITS
OPERATING CONSIDERATIONS
PAD Power™
T=RC
is a free Excel based
www.Thaler.com
PAD123
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