ISL6140 Intersil Corporation, ISL6140 Datasheet - Page 9

• Manufacturer Part Number: ISL6140
• Description: Negative Voltage Hot Plug Controller
• Manufacturer: Intersil Corporation

found, then consider 2 separate resistor dividers (one for
each pin; both from VDD to VEE). This also allows the user
to adjust or trim either trip point independently.
Note that the top of the resistor dividers is shown in Figure
29 as GND (Short pin). In a system where cards are plugged
into a backplane (or any other case where pins are plugged
into an edge connector) the user may want to take
advantage of the order in which pins make contact.
Typically, pins on either end of the card make contact first
(although you may not know which end is first). If you
combine that with designating a pin near the center as the
short pin GND, and make it shorter than the rest, then it
should be the last pin to make contact.
The advantage of doing this: the VDD and VEE pin
connections are made first. The IC is powered up, but since
the top of the resistor divider is still open, both the UV and
OV pins are pulled low to VEE, which will keep the gate off.
This allows the IC time to get initialized, and also allows the
power supply to charge up any input capacitance. By the
time the resistor divider makes contact, the power supply
voltage on the card is presumably stabilized, and the IC
ready to respond; when the UV pin reaches the proper
voltage, the IC will turn on the GATE of the FET, and starts
the controlled inrush current charging.
Note that this is not a requirement; if the IC gets powered at
the same time as the rest of the board, it should be able to
properly control the inrush current. But if finer control is
needed, there are many variables involved to consider: the
number of pins in the connector; the lengths of the pins; the
amount of mechanical play in the pin-to-connector interface;
the amount of extra time versus the shorter pin length; the
amount of input capacitance versus the ability of the power
supply to charge it; the manufacturing cost adder (if any) of
different length pins; etc.
Applications: PWRGD/PWRGD
The PWRGD/PWRGD outputs are typically used to directly
enable a power module, such as a DC/DC converter. The
PWRGD (ISL6140) is used for modules with active low
enable (L version); PWRGD (ISL6150) for those with active
high enable (H version). The modules usually have a pull-up
device built-in, as well as an internal clamp. If not, an
external pull-up resistor may be needed, since the output is
open drain. If the pin is not used, it can be left open.
For both versions, the PG comparator compares the DRAIN
pin to VEE (connected to the source of the FET); if the
voltage drop exceeds VPG (1.7V nominal), that implies the
drop across the FET is too high, and the PWRGD pin should
go in-active (power-NO-GOOD).
9
ISL6140, ISL6150
ISL6140 (L version; Figure 6): Under normal conditions
(DRAIN < VPG), the Q2 DMOS will turn on, pulling PWRGD
low, enabling the module.
When the DRAIN is too high, the Q2 DMOS will shut off
(high impedance), and the pin will be pulled high by the
external module (or an optional pull-up resistor or
equivalent), disabling the module. If a pull-up resistor is
used, it can be connected to any supply voltage that doesn’t
exceed the IC pin maximum ratings on the high end, but is
high enough to give acceptable logic levels to whatever
signal it is driving. An external clamp may be used to limit the
range.
The PWRGD can also drive an opto-coupler (such as a
4N25), as shown in Figure 7 or LED (Figure 8). In both
cases, they are on (active) when power is good. Resistors
R12 or R13 are chosen, based on the supply voltage, and
the amount of current needed by the loads.
VPG (1.7V)
(SECTION OF) ISL6140
(L VERSION)
(1.7V)
VPG
(SECTION OF) ISL6140
(L VERSION)
(1.7V)
(SECTION OF) ISL6140
(L VERSION)
VPG
+
-
+
-
+
-
FIGURE 7. ACTIVE LOW ENABLE OPTO-ISOLATOR
FIGURE 8. ACTIVE LOW ENABLE WITH LED
FIGURE 6. ACTIVE LOW ENABLE MODULE
+
-
+
-
+
-
VDD
VDD
VDD
Q2
VEE
Q2
VEE
Q2
VEE
PWRGD
DRAIN
PWRGD
DRAIN
PWRGD
DRAIN
CL
+
R12
OPTO
ACTIVE LOW
VIN+
ON/OFF
VIN-
MODULE
ENABLE
LED (GREEN)
R13
VOUT-
VOUT+
PWRGD