MAX15068 Datasheet, PDF (12/17 Pages) Maxim Integrated Products – Dual ORing, Single Hot-Swap Controller

MAX15068
Dual ORing, Single Hot-Swap Controller with
Accurate Current Monitoring
Detailed Description
Startup
When input voltage is applied to IN_, CSP comes up to
one diode below the higher of IN1 or IN2. The internal
LDO regulator powers V_S from the higher of two inputs as
well. When both V_S and CSP reach their respective UVLO
thresholds, the internal charge pumps (CP1 or CP2)
for the ORing controller start operating. An internal time
starts when both ON is above its threshold and EN is
below its threshold. After the timer counts 85ms, the
ORing control (OG1 or OG2) begins operating. After an-
other 15ms have elapsed, the hot-swap control (GATE)
also starts operating.
ORing Control
ORing Control in Startup
During a normal power-up, the ORing MOSFETs turn
on first. As soon as the internally generated supply, V_S,
rises above its undervoltage lockout threshold, the inter-
nal charge pump is allowed to charge up the CP_ pins.
Because the ideal diode MOSFETs are connected in par-
allel as a diode-OR, the CSP pin voltage selects the high-
est of the supplies at the IN1 and IN2 pins. The MOSFET
associated with the lower input supply voltage is turned
off by the corresponding gate drive amplifier.
At power-up the CP_ and OG_ pin voltages are at the
IN_ voltage level. CP_ starts ramping up after VS clears
its undervoltage lockout level. Afterward, OG_ ramps up
with CP_.
The gate drive amplifier monitors the voltage between the
IN and CSP pins and drives the respective OG_ pin.
If the amplifier senses a forward voltage drop greater than
80mV between IN and CSP then the OG_ pin is pulled to
CP to quickly turn on the MOSFET. If the amplifier senses
a reverse voltage drop greater than 10mV between CSP
and IN_, then the OG_pin is pulled to IN_ to quickly turn
off the MOSFET. With the ideal diode MOSFETs acting as
an input supply diode-OR, the CSP pin voltage rises to the
highest of the supplies at the IN1 and IN2 pins. The stored
charge in an external capacitor connected between the
CP_ and IN_ pins provides the charge needed to quickly
turn on and off the ideal diode MOSFET. An internal charge
pump charges the external capacitors at the CP pins. The
OG_ pin sources current from the CP_ pin and sinks cur-
rent into the IN_ and GND pins.
ORing MOSFET Regulation Mode
When the ideal diode MOSFET is turned on, the gate
drive amplifier controls OG_ to servo the forward voltage
drop (V_IN - V_CSP) across the MOSFET to 10mV. If the
load current causes more than 10mV of voltage drop,
across the FET, then the OG voltage rises to enhance the
MOSFET. For large output currents, the MOSFET’s gate
is driven fully on and the voltage drop is equal to I_LOAD x
R_DS(ON) of the MOSFET.
Hot-Swap Control
Hot-Swap in Startup
Once the output is enabled, the device provides controlled
application of power to the load. The voltage at OUT
begins to rise until the internal selected final maximum
current limit is reached, which is programmed through the
CB pin (Table 1). The low limit is approximately 1/12th of
the upper limit as shown in Figure 1. Once the power-
good threshold is achieved, the normalized hot-swap
electronic circuit-breaker (ECB) threshold goes to its full
value.
An external capacitor connected to the GATE pin allows
the user to program the slew rate to a value lower than the
default. During startup, a foldback current limit is active to
protect the external hot-swap MOSFET to operate within
the SOA (Figure 1).
An internal timer is activated to count for 70ms, which is
the maximum time duration for the startup phase. The
startup phase is completed when the voltage at OUT rises
above the power-good threshold (0.9 x VCSP typical)
and hot-swap GATE to OUT voltage exceeds 4.2V even
though the 70ms timeout has not yet elapsed.
Programmable Speed Circuit-Breaker
Response on Hot-Swap MOSFET
The device features an adjustable current limit with
circuit-breaker function that protects the external
MOSFETs against short circuits or excessive load current.
The voltage across the external sense resistor (R_SENSE)
is monitored by an electronic circuit breaker (ECB) and
Figu^VrCeB ^N1^ORMALIZE
THRESHOLD
0.6
0.5
0.4
0.3
0.2
0.1
2V
10V 12V
VCSN - VOUT
Figure 1. Inrush Current vs. Voltage Drop Across the Hot-Swap
Switch During Startup Period
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