MAX8725ETI+ Maxim Integrated Products, MAX8725ETI+ Datasheet - Page 21

• Manufacturer Part Number: MAX8725ETI+
• Description: IC CHARGER BATTERY 28-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8725ETI+

• Function: Charge Management
• Battery Type: Multi-Chemistry
• Voltage - Supply: 8 V ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN Exposed Pad
• Product: Charge Management
• Operating Supply Voltage: 8 V to 28 V
• Supply Current: 2.7 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• 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

• IMIN: Compares the control point (LVC) against
• IMAX: Compares the charge current (CSI) to the
• ZCMP: Compares the charge current (CSI) to 333mA
The MAX1909/MAX8725 control charge voltage (CCV
control loop), charge current (CCI control loop), or input
current (CCS control loop), depending on the operating
conditions. The three control loops, CCV, CCI, and CCS,
are brought together internally at the LVC amplifier. The
output of the LVC amplifier is the feedback control
signal for the DC-DC controller. The minimum
voltage at CCV, CCI, or CCS appears at the output of
the LVC amplifier and clamps the other two control
loops to within 0.3V above the control point. Clamping
the other two control loops close to the lowest control
loop ensures fast transition with minimal overshoot
when switching between different control loops (see the
Compensation section).
With sufficient battery current loading, the MAX1909/
MAX8725s’ inductor current never reaches zero, which
is defined as continuous conduction mode. If the BATT
voltage is within the following range:
the regulator is not in dropout and switches at f
400kHz. The controller starts a new cycle by turning on
the high-side p-channel MOSFET and turning off the
low-side n-channel MOSFET. When the charge current
is greater than the control point (LVC), CCMP goes high
and the off-time is started. The off-time turns off the
high-side p-channel MOSFET and turns on the low-side
n-channel MOSFET. The operating frequency is gov-
erned by the off-time and is dependent upon V
and V
Multichemistry Battery Chargers with Automatic
0.15V (typ). If IMIN output is low, then a new cycle
cannot begin. This comparator determines whether
the regulator operates in discontinuous mode.
internally fixed cycle-by-cycle current limit. The
current-sense voltage limit is 97mV. With RS2 =
0.015Ω, this corresponds to 6A. The high-side
MOSFET on-time is terminated if the IMAX output is
high and a new cycle cannot begin until IMAX goes
low. IMAX protects against sudden overcurrent
faults.
(RS2 = 0.015Ω). The current-sense voltage threshold
is 5mV. If ZCMP output is high, then both MOSFETs
are turned off. The ZCMP comparator terminates the
switch on-time in discontinuous mode.
3.1V
CCV, CCI, CCS, and LVC Control Blocks
BATT
✕
(number of cells) < V
. The off-time is set by the following equation:
Continuous Conduction Mode
______________________________________________________________________________________
BATT
< (0.88
✕
V
DCIN
NOM
DCIN
)
=
System Power Selector
where f
These equations describe the controller’s pseudo-fixed-
frequency performance over the most common operat-
ing conditions.
At the end of the fixed off-time, the controller can initiate
a new cycle if the control point (LVC) is greater than
0.15V (IMIN = high) and the peak charge current is less
than the cycle-by-cycle limit (IMAX = low). If the charge
current exceeds I
IMAX comparator.
If during the off-time the inductor current goes to zero,
ZCMP = high, both the high- and low-side MOSFETs
are turned off until another cycle is ready to begin. This
condition is discontinuous conduction. See the
Discontinuous Conduction section.
There is a minimum 0.3µs off-time when the (V
V
V
reached and the t
frequency in this mode varies according to the equation:
The MAX1909/MAX8725 enter discontinuous-conduc-
tion mode when the output of the LVC control point falls
below 0.15V. For RS2 = 0.015Ω, this corresponds to
0.5A:
BATT
DCIN
) differential becomes too small. If V
, then the threshold for minimum off-time is
NOM
f
= 400kHz:
where I
=
t
OFF
t
ON
MAX
t
I
MIN
OFF
OFF
RIPPLE
=
f
=
Discontinuous Conduction
, the on-time is terminated by the
=
⎛
⎜
⎝
=
f
NOM
V
is fixed at 0.3µs. The switching
V
t
CSSN
20
1
ON
CSSN
L I
0 15
×
.
=
×
V
+
V
RIPPLE
RS
1
V
BATT
CSSN
1
t
V
−
BATT
OFF
−
V
2
V
BATT
V
=
CSSN
BATT
L
0 5
−
×
.
V
t
BATT
OFF
A
+
1
⎞
⎟
⎠
BATT
≥ 0.88 x
DCIN
21
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