MAX8555AEUB-T Maxim Integrated Products, MAX8555AEUB-T Datasheet - Page 12

• Manufacturer Part Number: MAX8555AEUB-T
• Description: MOSFET & Power Driver ICs .5-3.3V ORing MOSFET Controller
• Manufacturer: Maxim Integrated Products

Specifications of MAX8555AEUB-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

(defined as V
MAX8555A discharge GATE to GND and FAULT is
latched low. If the I
OVP is disabled. In redundant systems, when one input
supply approaches its OVP threshold, some of the
other input supplies may be pulled up with it, thereby
tripping those OVP comparators with a slightly lower
set point. The I
supplies may not be detected until the first supply is
shut down. An alternate application schematic for
FAULT and OVP is shown in Figure 2. The FAULT
output of the first channel, which has both OVP and
I
OVP signal by 125mV. This ensures that only the input
supply, which is causing the overvoltage condition, is
turned off in a redundant power-system application.
Exceeding the OVP threshold causes the MAX8555/
MAX8555A to be latched off. Toggle V
reset the IC. Connect OVP to GND to disable the over-
voltage-protection feature.
Low-Cost, High-Reliability, 0.5V to 3.3V ORing
MOSFET Controllers
Table 1. Fault Modes
Figure 2. OVP Connection when Multiple MAX8555s Are Used
12
FORWARD
VL UVLO
UVP
Undervoltage Protection
OVP
Overvoltage Protection
Reverse-Current Protection
V
DD
______________________________________________________________________________________
Internal Overvoltage Protection
FAULT
OVP
FAULT MODE
conditions, temporarily reduces the common
6.04kΩ
R2B
CS+
FORWARD
R2A
47kΩ
150pF
FORWARD
> V
CS-
condition for the pulled-up
+ 0.01V), the MAX8555/
R5
2.87kΩ
R6
1kΩ
condition is not detected,
150pF
VL < VL
V
V
V
V
GATE is on for > 2048 charge-pump cycles
V
UVP
OVP
CS+
CS+
DD
R2A
47kΩ
> 14.5V
6.04kΩ
SYSTEM BUS
< 0.4V
DD
> 0.5V
> V
< V
R2B
OK
CS-
CS-
or TIMER to
FAULT
OVP
+ 0.01V
- 0.04V (0.02V for MAX8555A) and
CONDITIONS
The MAX8555/MAX8555A provide a reverse-current
fault-protection feature that turns off the oring MOSFET
when a reverse-current fault condition is detected.
Once a reverse-current fault condition is detected, the
MAX8555/MAX8555A discharge GATE to GND and
latch FAULT low. Toggle V
IC. The reverse-current-protection feature is blanked for
2048 charge-pump cycles at startup.
Connect a resistor from TIMER to GND to set the inter-
nal charge pump’s frequency of operation. Determine
the TIMER resistor with the following equation:
Drive TIMER above 1.5V for the maximum charge-
pump frequency (550kHz). Drive TIMER below 0.5V to
disable the charge pump and shut down the MAX8555/
MAX8555A.
The charge pump uses an internal monolithic transfer
capacitor to charge the external MOSFET gates.
Normally, the external MOSFET’s gate capacitance is
sufficient to serve as a reservoir capacitor. To slow down
turn-on times further, add a small capacitor between
GATE and GND. Adding a small resistor between GATE
and the gate of the Oring MOSFET reduces the high-fre-
quency ringing due to gate trace inductance. However,
the resistor increases the turn-off time.
Selecting the GATE Capacitor and
R
TIMER
Selecting the TIMER Resistor
GATE
LOW
LOW
LOW
LOW
LOW
=
100
DD
µ −
High Impedance
A
, VL, or TIMER to reset the
1 25
.
FAULT
Reverse-Current Fault
5
LOW
LOW
LOW
LOW
kHz
V
f
GATE Resistor
/
µ
A
LATCHING
YES
YES
NO
NO
NO