ltc4215-1 Linear Technology Corporation, ltc4215-1 Datasheet - Page 15

• Manufacturer Part Number: ltc4215-1
• Description: Hot Swap Controller With Adc And I2c Compatible Monitoring
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
by removal of the fault condition, the switch is allowed
to turn on again. The LTC4215-1 will set bit D2 and turn
off in the event of an overcurrent fault, preventing it from
remaining in an overcurrent condition. If confi gured to
auto-retry, the LTC4215-1 will continually attempt to re-
start after cool-down cycles until it succeeds in starting
up without generating an overcurrent fault.
Data Converter
The LTC4215-1 incorporates an 8-bit A/D converter that
continuously monitors three different voltages. The
SOURCE pin has a 1/12.5 resistive divider to monitor
a full scale voltage of 15.4V with 60mV resolution. The
ADIN pin is monitored with a 1.235V full scale and 4.82mV
resolution, and the voltage between the V
pins is monitored with a 38.6mV full scale and 151μV
resolution.
Results from each conversion are stored in registers E
(Sense), F (Source) and G (ADIN), as seen in Tables 6-8,
and are updated 10 times per second. Setting CONTROL
register bit A5 invokes a test mode that halts the data
converter so that registers E, F , and G may be written to
and read from for software testing.
Confi guring the GPIO Pins
Table 2 describes the possible states of the GPIO1 pin us-
ing the control register bits A6 and A7. At power-up, the
default state is for the GPIO1 pin to be a general purpose
output with output value set by bit B6 (default 1 = GPIO1
Hi-Z). Other applications for the GPIO1 pin are to go high
impedance when power is good (FB pin greater than
1.235V), pull down when power is good, and a general
purpose input. Digital input information can be read from
bit C6 (Table 4).
Table 3 is used to confi gure the GPIO2 pin as a fault
alert output (See Fault alerts) and also can be used as a
general purpose output and a general purpose input. By
default the GPIO2 pin is a general purpose output in the
high-impedance state as set by bit D6 (default 0 = GPIO2
Hi-Z, Table 5). Digital input information can be read from
bit C5 (Table 4).
The GPIO3 pin is a general purpose output/input that
defaults to output-low as set by bit D7 (default 1 = GPIO3
DD
and SENSE
pulled low, Table 5). Digital input information can be read
from bit C2 (Table 4).
Supply Transients
The LTC4215-1 is designed to ride through supply tran-
sients caused by load steps. If there is a shorted load and
the parasitic inductance back to the supply is greater than
0.5μH, there is a chance that the supply collapses before
the active current limit circuit brings down the GATE pin.
If this occurs, the undervoltage monitors pull the GATE
pin low. The undervoltage lockout circuit has a 2μs fi lter
time after V
2μs to shut the GATE off, but it is recommended to add a
fi lter capacitor C
by a transient. Eventually either the UV pin or undervoltage
lockout responds to bring the current under control before
the supply completely collapses.
Supply Transient Protection
The LTC4215-1 is safe from damage with supply voltages
up to 24V. However, spikes above 24V may damage the
part. During a short-circuit condition, large changes in
current fl owing through power supply traces may cause
inductive voltage spikes which exceed 24V. To minimize
such spikes, the power trace inductance should be mini-
mized by using wider traces or heavier trace plating. Also,
a snubber circuit dampens inductive voltage spikes. Build
a snubber by using a 100Ω resistor in series with a 0.1μF
capacitor between V
in Figure 1, at the input can also prevent damage from
voltage surges.
Design Example
As a design example, take the following specifi cations:
V
C
= 11.6V, and I
design is shown in Figure 1.
Selection of the sense resistor, R
threshold of 25mV:
IN
L
= 330μF , V
R
= 12V, I
S
=
25mV
I
MAX
MAX
DD
UV(ON)
2
C ADDRESS = 1001011. This completed
drops below 2.74V. The UV pin reacts in
= 5A, I
= 0.005
F
to prevent unwanted shutdown caused
= 10.75V, V
DD
INRUSH
and GND. A surge suppressor, Z1
= 1A, dI/dt
OV(OFF)
S
, is set by the overcurrent
LTC4215-1
= 14.0V, V
INRUSH
PWRGD(UP)
= 10A/ms,
15
42151f