adm1014 Analog Devices, Inc., adm1014 Datasheet - Page 8

• Manufacturer Part Number: adm1014
• Description: Dual Pci Hot-plugtm Controller
• Manufacturer: Analog Devices, Inc.

ADM1014
FUNCTIONAL DESCRIPTION
VOLTAGE OUTPUTS
The ADM1014 consists of two independent, identical chan-
nels, A and B, each of which controls four main power supply
voltages and an auxiliary voltage. As the channels are identical,
the following description applies to either channel, except
where otherwise stated.
An on-chip PMOS transistor connected between 12VIN and
12VO switches the +12V supply at currents up to 1.5A, whilst
an on-chip NMOS transistor connected between -12VIN and
-12VO switches the –12V supply at currents up to 0.38A. The
+3.3V and +5V supplies are switched by external, N-channel
MOSFETs, whose gate drive is provided by the 3V5VG pins.
Using suitable MOSFETs, singly or in parallel, currents of
several amps may be switched with very low voltage drops.
The four main power supplies may be switched on and off
under control of the PWRON pin.
The 3.3V auxiliary supply has an on-chip PMOS transistor,
which can switch currents at up to 1A. This supply is con-
trolled independently of the other four supplies by the
PAUXON pin.
All five supplies are protected against overcurrent and the four
positive supplies are also protected against undervoltage.
EXTERNAL CURRENT LIMIT
The external power MOSFETs are protected and overcurrent
shutdown is provided on the +3.3V and +5V supplies by exter-
nal current-sense resistors and on-chip comparators.
Current-sensing resistors are connected between the +5V out-
put pin and the 5VISEN pin, and between the +3.3V output
pin and the 3.3VISEN pin. The sense pins are connected to
the inverting inputs of the current-limit comparator directly,
while the voltage outputs are connected to the non-inverting
inputs via a reference voltage proportional to the voltage on the
OCSET pin. This voltage is V
output and V
values were chosen so that the 3.3V and 5V sense resistors
could both be 5m in PCI applications.
When the voltage drop across the current-sensing resistor ex-
ceeds the reference voltage, the output of the comparator will
go high, the fault latch will be set and all four main outputs and
the auxiliary output on the channel will be turned off. The
other main channel and auxiliary channel will remain on.
The reference voltages for the current-limit comparators are set
by connecting a resistor between the OCSET pin and GND.
An on-chip, 100µA current source generates a voltage across
this resistor. The current limit may also be adjusted by the
choice of current-sensing resistor.
I
I
Where:
I
R
R
LIMIT
LIMIT
LIMIT
SET
SENSE
is resistor from OCSET to GND in
(5V)
(3.3V) = V
= current limit in Amps
is current-sense resistor in
OCSET
= (R
= V
= (R
OCSET
OCSET
SET
SET
/11.5 in the case of the 3.3V output. These
/(11.5
/(14.5
10
10
-4
-4
)/(11.5
)/(14.5
OCSET
R
R
SENSE3
SENSE5
/14.5 in the case of the 5V
R
R
)
)
SENSE3
SENSE5
)
)
–8–
Note: The OCSET current source obtains its power supply
from 12VINA.
INTERNAL CURRENT LIMIT
The +3.3VAUX, +12V and –12V supplies have the power
MOSFET switches on-chip. These devices are protected and
overcurrent shutdown is provided by a completely self-contained
current sensing system. The output current through the on-chip
power MOSFET is tracked at a lower level by a second, smaller
MOSFET. The current through this MOSFET is then con-
verted to a voltage, which is compared to a reference voltage
determined by R
if the current-sense voltage exceeds this reference voltage, the
comparator output will go high, the fault latch will be set and
all four main outputs and the auxiliary output will be turned
off. Similarly in the case of the auxiliary output, if the current-
sense voltage exceeds the reference voltage, the comparator
output will go high, the fault latch will be set, FAUXN/FLTN
will go low, and the auxiliary output and the four main outputs
will turn off.
The typical internal limiting currents may be calculated as follows:
I
I
I
Where:
I
R
Due to tolerances in the current tracking FETs, the variations
in the internal current limit are quite wide, typically ±20% of
the calculated value for the +12V supply and +35/-20% of the
calculated value for the –12V supply.
CHOICE OF R
Using the above equations, R
current limits for the +3.3VAUX, +12V and -12V supplies. Once
R
current limits for the 3.3V and 5V outputs.
For PCI applications R
sense resistors should both be 5m ±1%. This will set the cur-
rent limits to the maximum values for the PCI specification.
For other applications, the following limits should be noted.
1. The minimum value of R
2. The maximum value of R
perature. This is determined by the power dissipated in the on-
chip MOSFETs, (which is dependent upon the current passed
LIMIT
LIMIT
LIMIT
LIMIT
SET
SET
voltage the current–limit comparators can reliably sense,
which is determined by noise, comparator offset voltage and
the overdrive required to switch the comparator. The refer-
ence voltage set by R
the 5V output, which has the smallest reference voltage.
The minimum recommended value for R
gives a reference voltage of 35mV for the 5V output and
45mV for the 3.3V output.
has been chosen, R
is resistor from OCSET to GND in
(+12V)
(-12V)
(+3.3VAUX) = V
= current limit in Amps
SET
SET
AND R
. In the case of the +12V and -12V outputs,
= (10-4
= 1.25
= 1.25
= V
= (10-4
SENSE3
SET
OCSET
OCSET
SET
SENSE
should be 6.04k and the current
SET
should not be less than 33mV for
SET
SET
and R
V
/3.3
/1.2
is chosen to set the required
R
10-4
OCSET
R
is limited by the minimum
is limited by the junction tem-
SET
SET
SENSE5
)/3.3
)/1.2
R
can be chosen to set the
SET
SET
is 6k , which
REV. PrN 1/02