AN008 Datasheet, PDF (1/9 Pages) Analog Intergrations Corporation – A Basis for LDO and It’s Thermal Design

AN008
A Basis for LDO and It’s Thermal Design
Introduction
The AIC LDO family device, a 3-terminal
regulator, can be easily used with all protection
features that are expected in high performance
voltage regulation application. These devices
provide short-circuit protection, thermal
shutdown protection and internal current limit
protection against any overload condition that
would create over heating junction temperature.
(1)Current Limit Protection
Like other power regulation IC, the AIC LDO
family has safety protection area. The current
limit protection works while outputting
heavy-loading current and keeps the output
current within a safe operating scope. The output
voltage decreases to a lower voltage level at the
same time. The AIC LDO family protection
function is designed to set up output current limit
when over-current happen and the downstream
devices can be protected from being damaged.
Figure 1 AIC1086 Current Limit Test
May 2000
Upper: output voltage (1V/DIV)
Lower: output current (2A/DIV)
(2) Protection Diodes
During normal operation, the AIC LDO device
needs no protection diode. The internal diode
between input and output pins can handle
microsecond surge current. Even with large
output capacitance, it is very difficult to get those
values of surge current in normal operation. The
damage will not occur, unless the high value
output capacitors and the input pin are shorted to
ground instantaneously. A crowbar circuit at the
input of the LDO device can generate those kinds
of current and a diode from output-to-input is then
recommended. Normal power supply cycling or
even plugging and unplugging in the system will
not generate sufficient large current to damage
device (see Figure 2).
AIC1086
Topology
D1
Function
V_IN
block
diagram
V_OUT
+
C_IN
+
C_OUT
Figure 2
Diagram
AIC1086 Protection Diodes
(3) Ripple Rejection
It is recommended to use the AIC LDO family
1