MAX17005/MAX17006/MAX17015
1.2MHz Low-Cost,
High-Performance Chargers
16 ______________________________________________________________________________________
CC, CCI, CCS, and LVC Control Blocks
The MAX17005/MAX17006/MAX17015 control input
current (CCS control loop), charge current (CCI control
loop), or charge voltage (CC control loop), depending
on the operating condition. The three control loops, CC,
CCI, and CCS are brought together internally at the
lowest voltage clamp (LVC) amplifier. The output of the
LVC amplifier is the feedback control signal for the
DC-DC controller. The minimum voltage at the CC, CCI,
or CCS appears at the output of the LVC amplifier and
clamps the other 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 differ-
ent control loops (see the
Compensation
section). The
CCS and CCI loops are compensated internally, and
the CC loop is compensated externally.
Continuous-Conduction Mode
With sufficiently large charge current, the MAX17005/
MAX17006/MAX17015s’ inductor current never crosses
zero, which is defined as continuous-conduction mode.
The controller starts a new cycle by turning on the high-
side MOSFET and turning off the low-side MOSFET.
When the charge-current feedback signal (CSI) is
greater than the control point (LVC), the CCMP com-
parator output goes high and the controller initiates the
off-time by turning off the high-side MOSFET and turn-
ing on the low-side MOSFET. The operating frequency
is governed by the off-time and is dependent upon
V
CSIN
and V
DCIN
.
The on-time can be determined using the following
equation:
where:
The switching frequency can then be calculated:
At the end of the computed off-time, the controller initi-
ates a new cycle if the control point (LVC) is greater
than 10mV (V
CSIP
- V
CSIN
referred), and the charge
current is less than the cycle-by-cycle current limit.
Restated another way, IMIN must be high, IMAX must
be low, and OVP must be low for the controller to initi-
ate a new cycle. If the peak inductor current exceeds
IMAX comparator threshold or the output voltage
exceeds the OVP threshold, then the on-time is termi-
nated. The cycle-by-cycle current limit effectively pro-
tects against overcurrent and short-circuit faults.
If during the off-time the inductor current goes to zero,
the ZCMP comparator output pulls high, turning off the
low-side MOSFET. Both the high- and low-side
MOSFETs are turned off until another cycle is ready to
begin. ZCOMP causes the MAX17005/MAX17006/
MAX17015 to enter into the discontinuous conduction
mode (see the
Discontinuous Conduction
section).
Discontinuous Conduction
The MAX17005/MAX17006/MAX17015 can also operate
in discontinuous conduction mode to ensure that the
inductor current is always positive. The MAX17005/
MAX17006/MAX17015 enter discontinuous conduction
mode when the output of the LVC control point falls below
10mV (referred at V
CSIP
- V
CSIN
). For RS2 = 10mΩ, this
corresponds to a peak inductor current of 1A.
In discontinuous mode, a new cycle is not started until
the LVC voltage rises above IMIN. 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 charger is in constant-voltage mode
with a nearly full battery pack.
Compensation
The charge voltage, charge current, and input current-
limit regulation loops are compensated separately. The
charge current and input current-limit loops, CCI and
CCS, are compensated internally, whereas the charge
voltage loop is compensated externally at CC.
