MAX17085BETL+T Maxim Integrated Products, MAX17085BETL+T Datasheet - Page 28

• Manufacturer Part Number: MAX17085BETL+T
• Description: Battery Management Dual Main Step-Down Controller
• Manufacturer: Maxim Integrated Products

Specifications of MAX17085BETL+T

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

Integrated Charger, Dual Main Step-Down
Controllers, and Dual LDO Regulators
The current-limit circuit employs a unique “valley” cur-
rent-sensing algorithm that senses the inductor current
through the low-side MOSFET, across LX to AGND. If the
current through the low-side MOSFET exceeds the valley
current-limit threshold, the PWM controller is not allowed
to initiate a new cycle. The actual peak current is greater
than the valley current-limit threshold by an amount
equal to the inductor ripple current. Therefore, the exact
current-limit characteristic and maximum load capability
are a function of the inductor value and battery voltage.
When combined with the UVP, this current-limit method
is effective in almost every circumstance.
The MAX17085B includes voltage soft-start and passive
soft-shutdown. During startup, the slew rate control softly
slews the internal target voltage over a 2ms startup peri-
od. This long startup period reduces the inrush current
during startup. Startup is always in skip mode regardless
of the SKIP pin setting.
When ON3 or ON5 is pulled low, or the output undervolt-
age fault latch is set, the regulator immediately forces DL
and DH low, and enables the internal 20I discharge FET
from the OUT pin to GND.
When
MAX17085B regulates the valley of the output ripple, so
the actual DC output voltage is lower than the slope com-
pensated trip level by 50% of the output ripple voltage.
For PWM operation (continuous conduction), the output
voltage is accurately defined by the following equation:
where V
V
x DI
Selection section).
In discontinuous conduction (I
the longer off-times allow the slope compensation to
increase the threshold voltage by as much as 1%, so the
output voltage regulates slightly higher than it would in
PWM operation.
28
RIPPLE
INDUCTOR
_____________________________________________________________________________________
the
NOM
is the output ripple voltage (V
inductor
is the nominal feedback voltage and
V
as described in the Output Capacitor
Valley Current-Limit Protection
OUT
Soft-Start and Soft-Shutdown
=
V
continuously
NOM
+
V
RIPPLE
OUT
2
Output Voltage
< I
conducts,
RIPPLE
LOAD(SKIP)
= ESR
the
),
PGOOD is the open-drain output that continuously moni-
tors the output voltage for undervoltage and overvoltage
conditions. PGOOD is actively held low when either
output voltage is more than 250mV (typ) below the nomi-
nal regulation threshold, during soft-start, in shutdown
(ON3 = ON5 = GND), and after either fault latch has
been tripped. After the soft-start circuit has terminated,
PGOOD becomes high impedance if the output is in
regulation plus 200Fs.
When only one SMPS is active, PGOOD monitors the
active SMPS output. When the 2nd SMPS is started,
PGOOD is blanked high-Z during the 2nd SMPS soft-start
plus 200Fs, then PGOOD monitors both SMPS outputs.
For a logic-level PGOOD output voltage, connect an
external pullup resistor between PGOOD and LDO3. A
100kI pullup resistor works well in most applications.
The main SMPS features overvoltage and undervoltage
fault protection that shuts down the SMPS. To prevent
false trips from latching off the main SMPS, the fault
latch is automatically reset after approximately 7ms. If
the ON pins are still high, the respective SMPS restarts.
If the fault is still present, the shutdown and restart cycle
repeats. After the 4th time, the latch is permanently set
and requires toggling ON3 or ON5, or pulling V
UVLO to start again.
The charger operation is not affected by the SMPS faults.
When the output voltage rises 16% above the fixed regu-
lation voltage, the controller immediately pulls PGOOD
low, sets the overvoltage fault latch, and immediately
pulls the respective DL high, clamping the output fault to
GND. The nonfaulted side also enters the shutdown state.
When the output voltage drops 30% below the fixed
regulation voltage and the inductor current exceeds the
current limit, the controller immediately pulls PGOOD
low, sets the undervoltage fault latch, and discharges
both SMPS outputs.
Power-Good Output (PGOOD)
Undervoltage Protection (UVP)
Overvoltage Protection (OVP)
Fault Protection
CC
below