MAX8765ETI+ Maxim Integrated Products, MAX8765ETI+ Datasheet - Page 21

• Manufacturer Part Number: MAX8765ETI+
• Description: IC CHARGER BATTERY 28-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8765ETI+

• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In normal operation, the controller starts a new cycle by
turning on the high-side n-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 n-channel MOSFET and
turns on the low-side n-channel MOSFET. The opera-
tional frequency is governed by the off-time and is
dependent upon V
by the following equations:
where:
These equations result in fixed-frequency operation
over the most common operating conditions.
At the end of the fixed off-time, another cycle begins if
the control point (LVC) is greater than 0.15V, IMIN =
high, and the peak charge current is less than 6A (RS2
= 0.015Ω), IMAX = high. If the charge current exceeds
IMAX, the on-time is terminated by the IMAX compara-
tor. IMAX governs the maximum cycle-by-cycle current
limit and is internally set to 6A (RS2 = 0.015Ω). IMAX
protects against sudden overcurrent faults.
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.
There is a minimum 0.3µs off-time when the (V
V
V
reached and the t
time of 5ms allows the controller to achieve > 99% duty
cycle in continuous-conduction mode. The switching
frequency in this mode varies according to the equation:
BATT
DCIN
) differential becomes too small. If V
, then the threshold for minimum off-time is
Low-Cost Multichemistry Battery Chargers
t
OFF
f
I
=
RIPPLE
t
ON
(
=
OFF
______________________________________________________________________________________
V
DCIN
2 5 . µ
CSSN
f
L I
=
=
is fixed at 0.3µs. A maximum on-
×
V
=
t
s
CSSN
ON
RIPPLE
and V
L I
×
−
V
BATT
×
V
V
+
1
BATT
DCIN
RIPPLE
1
t
−
OFF
BATT
L
V
V
×
DCIN
BATT
)
t
−
OFF
+
. The off-time is set
V
0 3 . µ
BATT
s
BATT
≥ 0.88 ×
DCIN
-
The MAX1908/MAX8724/MAX8765/MAX8765A enter dis-
continuous-conduction mode when the output of the LVC
control point falls below 0.15V. For RS2 = 0.015Ω, this
corresponds to 0.5A:
for RS2 = 0.015Ω.
In discontinuous mode, a new cycle is not started until
the LVC voltage rises above 0.15V. Discontinuous-
mode operation can occur during conditioning charge
of overdischarged battery packs, when the charge cur-
rent has been reduced sufficiently by the CCS control
loop, or when the battery pack is near full charge (con-
stant-voltage-charging mode).
The low-side driver output DLO switches between
PGND and DLOV. DLOV is usually connected through
a filter to LDO. The high-side driver output DHI is boot-
strapped off LX and switches between V
When the low-side driver turns on, BST rises to one
diode voltage below DLOV.
Filter DLOV with a lowpass filter whose cutoff frequency
is approximately 5kHz (Figure 1):
The MAX1908/MAX8724/MAX8765/MAX8765A have 99%
duty-cycle capability with a 5ms (max) on-time and 0.3µs
(min) off-time. This allows the charger to achieve dropout
performance limited only by resistive losses in the DC-DC
converter components (D1, N1, RS1, and RS2, Figure 1).
Replacing diode D1 with a p-channel MOSFET driven by
ACOK improves dropout performance (Figure 2). The
dropout voltage is set by the difference between DCIN
and CSIN. When the dropout voltage falls below 100mV,
the charger is disabled; 200mV hysteresis ensures that
the charger does not turn back on until the dropout volt-
age rises to 300mV.
Each of the three regulation loops—input current limit,
charging current limit, and charging voltage limit—are
compensated separately using CCS, CCI, and CCV,
respectively.
f
C
=
2
π
IMIN
1
RC
=
=
Discontinuous Conduction
2
20
π
0 15
×
.
×
33
RS
V
1
Ω
2
×
=
1
µ
0 5
F
.
Dropout Operation
=
A
MOSFET Drivers
4 8
.
Compensation
kHz
LX
and V
BST
21
.