MAX8725ETI Maxim Integrated Products, MAX8725ETI Datasheet - Page 19

• Manufacturer Part Number: MAX8725ETI
• Description: Battery Management Multichemistry Battery Charger
• Manufacturer: Maxim Integrated Products

Specifications of MAX8725ETI

• Product: Charge Management
• Battery Type: Li-Ion, Li-Polymer, NiCd, NiMH, Lead Acid, Universal
• Operating Supply Voltage: 8 V to 28 V
• Supply Current: 2.7 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: TQFN-28
• Charge Safety Timers: No
• Mounting Style: SMD/SMT
• Temperature Monitoring: No
• Uvlo Start Threshold: 9.18 V
• Uvlo Stop Threshold: 9.42 V
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The body diode of the PDL switch prevents the voltage
on the power source output from collapsing.
Charging can also be inhibited by driving ICTL below
0.035V, which suspends switching and pulls CCI, CCS,
and CCV to ground. The PDS and PDL drivers, LDO,
input current monitor, and control logic (ACOK) all
remain active in this state. Approximately 3mA of sup-
ply current is drawn from the AC adapter and 3µA
(max) is drawn from the battery to support these
functions.
In smart-battery systems, PKPRES is usually driven from a
voltage-divider formed with a low-value resistor or PTC
thermistor inside the battery pack and a local resistive
pullup. This arrangement automatically detects the pres-
ence of a battery. The MAX8725 threshold voltage is 55%
of V
transitions.
The MAX1909/MAX8725 include a hysteretic compara-
tor that detects the presence of an AC power adapter
and automatically delivers power to the system load
from the appropriate available power source. When the
adapter is present, the open-drain ACOK output
becomes high impedance. The switch threshold at
ACIN is 2.048V. Use a resistive voltage-divider from the
adapter’s output to the ACIN pin to set the appropriate
detection threshold. When charging, the battery is iso-
lated from the system load with the p-channel PDL
switch, which is biased off. When the adapter is absent,
the drives to the switches change state in a fast break-
before-make sequence. PDL begins to turn on 7.5µs
after PDS begins to turn off.
The threshold for selecting between the PDL and PDS
switches is set based on the voltage difference
between the DCIN and the BATT pins. If this voltage
difference drops below 100mV, the PDS is switched off
and PDL is switched on. Under these conditions, the
MAX1909/MAX8725 are completely powered down.
The PDL switch is kept on with a 100kΩ pulldown resis-
tor when the charger is powered down through ICTL or
PKPRES, or when the AC adapter is removed.
The drivers for PDL and PDS are fully integrated. The pos-
itive bias inputs for the drivers connect to the SRC pin and
the negative bias inputs connect to a negative regulator
referenced to SRC. With this arrangement, the drivers can
swing from SRC to approximately 10V below SRC.
Multichemistry Battery Chargers with Automatic
LDO
, with hysteresis of 1% V
______________________________________________________________________________________
AC Adapter Detection and
Power-Source Selection
LDO
to prevent erratic
System Power Selector
The MAX1909/MAX8725 can be programmed to per-
form a conditioning cycle to calibrate the battery’s fuel
gauge. This cycle consists of isolating the battery from
the charger and discharging it through the system load.
When the battery reaches 100% depth of discharge, it
is then recharged. Driving the MODE pin low places the
MAX1909/MAX8725 in conditioning mode, which stops
the charger from switching, turns the PDS switch off,
and turns the PDL switch on.
To utilize the conditioning mode function, the configura-
tion of the PDS switch must be changed to two source-
connected FETs to prevent the AC adapter from sup-
plying current to the system through the MOSFET’s
body diode. See Figure 2. The SRC pin must be con-
nected to the common source node of the back-to-back
FETs to properly drive the MOSFETs.
It is essential to alert the user that the system
is performing a conditioning cycle. If the user termi-
nates the cycle prematurely, the battery can be dis-
charged even though the system was running off the
AC adapter for a substantial period of time. If the AC
adapter is in fact removed during conditioning, the
MAX1909/MAX8725 keep the PDL switch on and the
charger remains off as it would in normal operation.
In the MAX8725, if the battery is removed during condi-
tioning mode, the PKPRES control overrides condition-
ing mode. When MODE is grounded and PKPRES goes
high, the PDS switch starts turning on within 7.5µs and
the system is powered from the AC adapter.
In the MAX1909, disable conditioning mode before the
battery is overdischarged or removed.
The MAX1909/MAX8725 employ a buck regulator with a
PMOS high-side switch and a low-side NMOS synchro-
nous rectifier. The MAX1909/MAX8725 feature a pseu-
do-fixed-frequency, cycle-by-cycle current-mode
control scheme. The off-time is dependent upon V
V
300ns. The MAX1909/MAX8725 can also operate in
discontinuous conduction for improved light-load effi-
ciency. The operation of the DC-DC controller is deter-
mined by the following four comparators as shown in
Figure 4:
• CCMP: Compares the control point (lowest voltage
BATT
clamp (LVC)) against the charge current (CSI). The
high-side MOSFET on-time is terminated if the CCMP
output is high.
, and a time constant, with a minimum t
DC-DC Converter
Conditioning Mode
OFF
DCIN
19
of
,