MAX17085BETL+T Maxim Integrated Products, MAX17085BETL+T Datasheet - Page 32

• 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
where K is a function of maximum duty cycle (lowest
input voltage) and switching frequency as shown in
Figure 6.
The amount of overshoot during a full-load to no-load tran-
sient due to stored inductor energy can be calculated as:
The minimum current-limit threshold must be great
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The valley
of the inductor current occurs at I
the ripple current; therefore:
where I
threshold voltage divided by the current-sense element
(low-side R
Connect a resistor-divider from REF to ILIM to analog
ground (AGND) to set the adjustable current-limit thresh-
old. The valley current-limit threshold is approximately
1/10 the ILIM voltage over a 0.2V to 2.1V range. The
adjustment range corresponds to a 20mV to 210mV val-
ley current-limit threshold. When adjusting the current
limit, use 1% tolerance resistors to prevent significant
inaccuracy in the valley current-limit tolerance.
Figure 6. Scale Factor vs. Duty Cycle
32
_____________________________________________________________________________________
I
LIM(VAL )
LIM(VAL)
100
10
DSON
1
0.5
V
SOAR
equals the minimum valley current-limit
>
).
I
LOAD(MAX)
0.6
800kHz
≈
(
Setting the Current Limit
D
600kHz
0.7
DUTY CYCLE
I
2C
LOAD(MAX)
OUT OUT
400kHz 200kHz
-




0.8
I
V
LOAD(MAX)
LOAD(MAX)
)
2
0.9
2
L
LIR
minus half
1.0




The input capacitor and MOSFET selection criteria share
common considerations for the charger and the main
SMPS. For the following sections, V
charger and V
the charger and V
I
The input capacitor must meet the ripple-current require-
ment (I
For most applications, nontantalum chemistries (ceramic,
aluminum, or OS-CON) are preferred due to their resis-
tance to power-up surge currents typical of systems with
a mechanical switch or connector in series with the input.
In either configuration, choose a capacitor that has less
than 10NC temperature rise at the RMS input current for
optimal reliability and lifetime.
The conduction loss in the high-side MOSFET (N
a function of the duty factor, with the worst-case power
dissipation occurring at the minimum input voltage, and
maximum output voltage in the case of the charger:
Calculating the switching losses in high-side MOSFET
(N
ing factors that influence the turn-on and turn-off times.
These factors include the internal gate resistance, gate
charge, threshold voltage, source inductance, and PCB
layout characteristics. The following switching-loss cal-
culation provides only a very rough estimate and is no
substitute for breadboard evaluation, preferably includ-
ing verification using a thermocouple mounted on N
where C
Q
and I
The following high-side MOSFET’s loss is due to the reverse-
recovery charge of the low-side MOSFET’s body diode:
OUT
G(SW)
H
PD
) is difficult since it must allow for difficult quantify-
GATE
is I
SW
RMS
CHG
PD
is the charge needed to turn on the N
(HS)
OSS
is the peak gate-drive source/sink current (2A typ).
I
RMS
) imposed by the switching currents:
COND
Common Design Procedure
for the charger and I
=
is the N
SYS
V I
=
High-Side MOSFET Power Dissipation
IN OUT SW
(HS)
I
OUT5
LOAD
for the main SMPS, V
=
H
f
or V
Input Capacitor Selection
Power-MOSFET Selection




V
V
OUT
MOSFET’s output capacitance,
IN
V




OUT3
OUT
Q
I
GATE
G(SW)
×
I
LOAD
(
OUT
V
V
for the main SMPS, and
IN
IN




IN
- V
2
+
for the main SMPS.
×
OUT
C
is V
OUT
R
OSS IN SW
DS(ON)
)
DCIN
is V




V
H
2
MOSFET,
BATT
2
for the
f
H
H
) is
:
for