13-3087; Rev 0; 1/04
IT
TION K
VALUA
E
BLE
AVAILA
Low-Cost, High-Reliability, 0.5V to 3.3V ORing
MOSFET Controllers
General Description
Critical loads often employ parallel-connected power
supplies with redundancy to enhance system reliability.
The MAX8555/MAX8555A are highly integrated, inex-
pensive MOSFET controllers that provide isolation and
redundant power capability in high-reliability systems.
The MAX8555/MAX8555A are used in 0.5V to 3.3V sys-
tems, and have an internal charge pump to drive the
gates of the N-channel pass elements to (V
CS+
+ 5V).
During startup, the MAX8555/MAX8555A monitor the
voltage drop across the external MOSFETs. Once V
CS+
approaches or exceeds the bus voltage (V
CS-
), the
MOSFETs are turned on. The MAX8555/MAX8555A fea-
ture a dual-purpose TIMER input. A single external
resistor from TIMER to ground sets the turn-on speed of
the external MOSFETs. Optionally, the TIMER input can
be used as a logic enable input. Once the external
MOSFET is turned on, these controllers monitor the
load, protecting the bus against overvoltage, undervolt-
age, and reverse-current fault conditions. The
MAX8555 is available with a 40mV reverse-current
threshold, while the MAX8555A is available with a 20mV
reverse-current threshold.
Overvoltage and undervoltage fault thresholds are
adjustable and can be disabled. The current-limit trip
points are set by the external MOSFETs’ R
DS(ON)
,
reducing component count. An open-drain, logic-low
fault output indicates if an overvoltage, undervoltage, or
reverse-current fault occurs. The MAX8555 and the
MAX8555A can shut down in response to a reverse-
current fault condition as quickly as 200ns.
Both devices come in space-saving 10-pin µMAX or
TDFN packages and are specified over the extended
-40°C to +85°C temperature range.
Features
♦
Simple, Integrated, and Inexpensive MOSFET
Controllers
♦
ORing FET Drive for 0.5V to 3.3V
♦
Eliminate ORing Diode Power Dissipation
♦
Provide N+1 Redundant Supply Capability for
Highly Reliable Systems
♦
Isolate Failed Short-Circuit Supply from
Output BUS
♦
Respond to Reverse Short-Circuit Current
in 200ns
♦
Adjustable Blank Time
♦
Programmable Soft-Start
♦
Logic Enable Input
♦
Adjustable Overvoltage and Undervoltage
Trip Points
♦
Fault-Indicator Output
♦
Space-Saving Packages
MAX8555/MAX8555A
Ordering Information
PART
MAX8555ETB
MAX8555EUB
MAX8555AETB
MAX8555AEUB
TEMP
RANGE
-40°C to 85°C
-40°C to 85°C
-40°C to 85°C
-40°C to 85°C
PIN-
PACKAGE
10 TDFN
3mm x 3mm*
10 µMAX
10 TDFN
3mm x 3mm*
10 µMAX
TOP
MARK
ACC
8555EUB
ADD
8555AEUB
Applications
Point-of-Load Supplies
Power-Supply Modules
Servers
Telecom Power Supplies
Rectifiers
Redundant Power Supplies in High-Availability
Systems
*Exposed
paddle
Pin Configurations
TOP VIEW
GATE 1
GND
VL
V
DD
UVP
2
3
4
5
10 CS+
9
CS-
OVP
FAULT
TIMER
GATE
GND
VL
V
DD
UVP
1
2
3
4
5
10 CS+
MAX8555/
MAX8555A
8
7
6
MAX8555/
MAX8555A
9 CS-
8 OVP
7 FAULT
6 TIMER
Typical Operating Circuit appears at end of data sheet.
µMAX
TDFN
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Low-Cost, High-Reliability, 0.5V to 3.3V ORing
MOSFET Controllers
MAX8555/MAX8555A
ABSOLUTE MAXIMUM RATINGS
GATE to GND .........................................................-0.3V to +12V
FAULT,
VL to GND ...................................................-0.3V to +6V
OVP, UVP, TIMER, CS+, CS- to GND .......-0.3V to +(V
VL
+ 0.3V)
V
DD
to GND..................................................(V
VL
- 0.3V) to +18V
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW
10-Pin TDFN (derate 24.4mW/°C above +70°C) .......1951mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DD
= 12V, V
CS-
= 1.4V, V
CS+
= 1.5V, R
TIMER
= 25kΩ, V
UVP
= 1V, V
OVP
= 0.25V, R
FAULT
= 50kΩ, C
VDD
= C
GATE
= C
VL
= 0.01µF,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
V
DD
SUPPLY
V
DD
Input Voltage
V
DD
Supply Current
V
DD
Shutdown Current
V
DD
Overvoltage Internal
Threshold
VL SUPPLY
VL Input Voltage
VL Supply Current
VL Current in Shutdown Mode
VL Output Voltage
VL Undervoltage Lockout
CS INPUTS
CS+, CS- Input Current
Offset Input Current (CS+, CS-)
CS+/CS- Input Range
CS Isolation
CHARGE-PUMP VOLTAGE
GATE Voltage, V
GATE
Measured from GATE to CS+
R
TIMER
= 20kΩ
Charge-Pump Switching
Frequency
R
TIMER
= 125kΩ
R
TIMER
= open
V
TIMER
= 1.5V
V
DD
= 8V to 13.25V
V
DD
= V
VL
= 5V
5.0
5.25
187
450
500
550
kHz
5.5
V
V
TIMER
= 2.5V, V
CS
= 3.0V
V
CS
= 3.0V, Figure 4
(Note 1)
V
CS+
= +3V, V
CS-
= 0V, I
CS-
V
CS-
= +3V, V
CS+
= 0V, I
CS+
-250
0.5
-0.5
-0.5
5.2
+250
V
VL
- 0.5
µA
nA
V
µA
V
DD
= V
VL
V
DD
= V
VL
= 5V, V
TIMER
= 2.5V
TIMER = GND, V
DD
= V
VL
= 5V
V
DD
= 8V to 13.25V, I
VL
= 0A
VL = V
DD
, rising threshold
VL = V
DD
, falling threshold
3.80
2.78
2.68
3.0
1.8
1.6
4.1
2.82
2.75
5.5
3.0
3.0
4.45
2.90
2.82
V
mA
mA
V
V
V
TIMER
= 2.5V
VL unconnected
VL = V
DD
8.00
3.0
2.0
0.04
14.0
13.3
14.4
13.8
13.25
5.5
3.3
0.2
3.0
15.0
14.5
V
mA
mA
V
CONDITIONS
MIN
TYP
MAX
UNITS
VL unconnected, V
TIMER
= 2.5V, V
DD
= 13.25V
V
DD
= V
VL
= 5V, V
TIMER
= 2.5V
V
TIMER
= 0V, V
DD
= 13.25V
Rising threshold
Falling threshold
2
_______________________________________________________________________________________
Low-Cost, High-Reliability, 0.5V to 3.3V ORing
MOSFET Controllers
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 12V, V
CS-
= 1.4V, V
CS+
= 1.5V, R
TIMER
= 25kΩ, V
UVP
= 1V, V
OVP
= 0.25V, R
FAULT
= 50kΩ, C
VDD
= C
GATE
= C
VL
= 0.01µF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
TIMER
TIMER Voltage
TIMER Maximum Source Current
TIMER High Input Current
TIMER Maximum Frequency
Select Voltage Input Range
TIMER Logic High, V
IH
TIMER Logic Low, V
IL
FAULT
Fault Output Low Voltage
Fault Sink Current
GATE
Gate-On Threshold
Gate-Drive Current
Gate Shutdown Delay
CURRENT SENSE
Reverse-Current Threshold
Forward-Current Threshold
OVERVOLTAGE PROTECTION
OVP Fault Threshold, V
OVP
UNDERVOLTAGE PROTECTION
UVP Fault Threshold, V
UVP
UVP rising
0.488
0.512
V
OVP rising
0.49
0.51
V
Measured from CS- to CS+
Measured from CS+ to CS-
MAX8555
MAX8555A
34
16
6
46
24
14
mV
mV
Measured from CS- to CS+
V
GATE
= V
CS+
= 2.5V
MAX8555
MAX8555A
R
TIMER
= open
R
TIMER
= 25kΩ
V
TIMER
falling
I
REV
fault
80
35
17
8
120
65
33
16
200
150
mV
µA
ns
I
FAULT
= 10mA
V
FAULT
= 0.4V
15
0.2
V
mA
V
TIMER
= 1.0V
V
TIMER
= 1.5V
(Note 1)
Charge pump enabled
Charge pump disabled
1.5
1.1
0.5
1.22
85
1.28
115
15
V
VL
V
µA
µA
V
V
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8555/MAX8555A
Note 1:
Guaranteed by design. Not production tested.
Note 2:
Gate shutdown delay is measured from reverse-current fault to the start of gate-voltage falling or from TIMER to the start of
gate-voltage falling.
Note 3:
Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
5
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