MAX8671XETL+ Maxim Integrated Products, MAX8671XETL+ Datasheet - Page 33

• Manufacturer Part Number: MAX8671XETL+
• Description: IC PMIC W/CHARGER 40-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8671XETL+

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion), Lithium-Polymer (Li-Pol)
• Voltage - Supply: 4.1 V ~ 6.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 40-WFQFN Exposed Pad
• Mounting Style: SMD/SMT
• Input Voltage: 2.6 V to 6.6 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Output Current: 0.5 A
• Output Voltage: 0.6 V to 5 V
• Supply Current: 0.285 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX8671X uses external resistor-dividers to set the
step-down output voltages between 1V and V
least 10µA of bias current in these dividers to ensure no
change in the stability of the closed-loop system. To set
the output voltage, select a value for the resistor con-
nected between FB_ and AGND (R
mended value is 100kΩ. Next, calculate the value of the
resistor connected from FB_ to the output (R
REG1, REG2, and REG3 are optimized for high, medi-
um, and low output voltages, respectively. The highest
overall efficiency occurs with V1 set to the highest out-
put voltage and V3 set to the lowest output voltage.
The MAX8671X operates in either auto-PWM or forced-
PWM modes. At light load, auto PWM switches only as
needed to supply the load to improve light-load effi-
ciency of the step-down converter. At higher load cur-
rents (~100mA), the step-down converter transitions to
fixed 2MHz switching. Forced PWM always operates
with a constant 2MHz switching frequency regardless
of the load. This is useful in low-noise applications.
Permanently connect PWM high for forced-PWM appli-
cations or low for auto-PWM applications. Do not
change PWM on-the-fly.
All the step-down regulators are capable of operating
in 100% duty-cycle dropout; however, REG1 has been
optimized for this mode of operation. During 100%
duty-cycle operation, the high-side p-channel MOSFET
turns on constantly, connecting the input to the output
through the inductor. The dropout voltage (V
culated as follows:
where:
R
R
The minimum duty cycle for all step-down regulators is
12.5% (typ), allowing a regulation voltage as low as 1V
over the full SYS operating range. REG3 is optimized
for low duty-cycle operation.
The input capacitor in a step-down converter reduces
current peaks drawn from the power source and
P
L
= external inductor ESR
= p-channel power switch R
Step-Down Dropout and Minimum Duty Cycle
Smart Power Selector for Handheld Devices
V
R
DO
FBH
______________________________________________________________________________________
= I
=
R
LOAD
FBL
Step-Down Input Capacitors
×
(R
⎛
⎜
⎝
DS(ON)
P
V
1 0
PMIC with Integrated Charger and
OUT
.
+ R
V
L
FBL
−
)
1
⎞
⎟
⎠
). The recom-
FBH
SYS
DO
):
) is cal-
. Use at
PWM
reduces switching noise in the controller. The imped-
ance of the input capacitor at the switching frequency
must be less than that of the source impedance of the
supply so that high-frequency switching currents do not
pass through the input source.
The step-down regulator power inputs are critical dis-
continuous current paths that require careful bypass-
ing. In the PCB layout, place the step-down regulator
input bypass capacitors as close as possible to each
pair of switching regulator power input pins (PV_ to
PG_) to minimize parasitic inductance. If making con-
nections to these caps through vias, be sure to use
multiple vias to ensure that the layout does not insert
excess inductance or resistance between the bypass
cap and the power pins.
The input capacitor must meet the input ripple current
requirement imposed by the step-down converter.
Ceramic capacitors are preferred due to their low ESR
and resilience to power-up surge currents. Choose the
input capacitor so that its temperature rise due to input
ripple current does not exceed about +10°C. For a
step-down DC-DC converter, the maximum input ripple
current is half of the output current. This maximum input
ripple current occurs when the step-down converter
operates at 50% duty factor (V
Bypass each step-down regulator input with a 4.7µF
ceramic capacitor from PV_ to PG_. Use capacitors
that maintain their capacitance over temperature and
DC bias. Ceramic capacitors with an X7R or X5R tem-
perature characteristic generally perform well. The
capacitor voltage rating should be 6.3V or greater.
The output capacitance keeps output ripple small and
ensures control loop stability. The output capacitor
must have low impedance at the switching frequency.
Ceramic, polymer, and tantalum capacitors are suit-
able, with ceramic exhibiting the lowest ESR and lowest
high-frequency impedance. The MAX8671X requires at
least 20µF of output capacitance, which is best
achieved with two 10µF ceramic capacitors in parallel.
As the case sizes of ceramic surface-mount capacitors
decrease, their capacitance vs. DC bias voltage char-
acteristic becomes poor. Due to this characteristic, it is
possible for 0805 capacitors to perform well while 0603
capacitors of the same value might not. The MAX8671X
requires a nominal output capacitance of 20µF; howev-
er, after their DC bias voltage derating, the output
capacitance must be at least 15µF.
Step-Down Output Capacitors
IN
= 2 x V
OUT
).
33