MAX17085BETL+T Maxim Integrated Products, MAX17085BETL+T Datasheet - Page 23

• 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

If there are two clock edges on ISET within 20ms, the
PWM filter is enabled and ISET accepts digital PWM
input. The PWM filter accepts the digital signal with a
frequency from 128Hz to 500kHz. Zero duty cycle shuts
down the MAX17085B, and the 99% duty cycle cor-
responds to full scale (100mV) across CSIP and CSIN.
The PWM filter has a DAC with 8-bit resolution that corre-
sponds to equivalent V
Choose a current-sense resistor (RS2) to have a suf-
ficient power dissipation rating to handle the full-charge
current. The current-sense voltage may be reduced to
minimize the power dissipation period. However, this
may degrade accuracy due to the current-sense ampli-
fier’s input offset (200µV). See the Typical Operating
Characteristics to estimate the charge-current accuracy
at various set points.
The total input current, from a wall adapter or other DC
source, is the sum of the system supply current and
the current required by the charger. When the input
current exceeds the set input current limit, the control-
ler decreases the charge current to provide priority to
system load current. System current normally fluctuates
as portions of the system are powered up or down. The
input-current-limit circuit reduces the power requirement
of the AC wall adapter, which reduces adapter cost. As
the system supply rises, the available charge current
drops linearly to zero. Thereafter, the total input current
can increase without limit. The total input current can be
estimated as follows:
where E is the efficiency of the DC-to-DC converter (typi-
cally 85% to 95%).
In the MAX17085B, the voltage across CSSP and CSSN
is constant at 60mV. Choose the current-sense resistor,
RS1, to set the input current limit. For example, for 4A
input current limit choose RS1 = 15mI. For the input
current-limit settings, which cannot be achievable with
standard sense resistor values, use a resistive voltage-
divider between CSSP and CSSN to tune the setting.
V
STEP
=
256 21
V
I
INPUT
REF
Integrated Charger, Dual Main Step-Down
⋅
______________________________________________________________________________________
=
=
0.391mV (7.8mA with RS2 20m )
I
LOAD
CSIP
Controllers, and Dual LDO Regulators
- V
Setting Input Current Limit
+
Input Source Current
I
CHG
CSIN
V
ADP
×
steps. Each step is:
V
× η
BATT
Digital ISET
=
Ω
When the input current is 1.3 times the input current-limit
setting, PDSL is pulled to GND after a 16ms blanking
time. This turns off the adapter switch and enables the
battery selector switch. After 0.6s, PDSL is reenabled. If
the fault condition persists, the cycle is repeated, until
the third time when the charger is latched off. To clear
the fault latch, remove the adapter and allow DCIN to fall
below its UVLO threshold before reinserting the adapter.
IINP monitors the system-input current, which is sensed
across CSSP and CSSN. The voltage at IINP is propor-
tional to the input current:
where I
er, G
(60V/V typ), and RS1 is the resistor connected between
CSSP and CSSN.
When the adapter is absent, drive ISET above 2.1V to
enable IINP during battery discharge.
The ACIN input goes to two internal comparators, one
for adapter detection (ACOK) and another for adapter
overvoltage detection (ACOV). When ACIN is above
1.5V, the open-drain ACOK output becomes low imped-
ance after 44ms.
When ACIN rises above 2.1V, the MAX17085B detects
an ACOV condition and immediately pulls PDSL to GND,
turning off the adapter selection switch and enabling the
battery selector switch. This protects the system rail from
excessively high voltages that might violate the absolute
maximum ratings of the downstream components. Note
that ACOK remains low even when ACIN is above the
ACOV threshold.
Use a resistive voltage-divider from the adapter’s output
to the ACIN pin to set the appropriate detection thresh-
old. Connect a 100kI pullup resistor between LDO3 or
LDO5 and ACOK.
The MAX17085B integrates a charge pump to drive the
gate of n-channel adapter selector switches (N3 and
Q1a) and the p-channel battery-selector switch (Q1b).
When the adapter is present, PDSL is driven 8V above
V
the Operating Conditions section for the definition of
adapter present.
DCIN
Automatic Power-Source Selection (PDSL)
IINP
so that N3 and Q1a are on, and Q1b is off. See
ADP
is the transconductance of the sense amplifier
is the DC current supplied by the AC adapt-
V
IINP
V
IINP
Analog Input Current-Monitor Output
=
=
60
AC Adapter Overcurrent (ACOC)
G
×
IINP
(
V
CSSP
AC Adapter Detection
×
(ACIN, ACOK, ACOV)
I
ADP
- V
×
CSSN
RS1
)
23