1.2MHz, Low-Cost,

High-Performance Chargers

16

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CC, CCI, CCS, and LVC Control Blocks

The MAX17005B/MAX17006B/MAX17015B control

input current (CCS control loop), charge current (CCI

control loop), or charge voltage (CC control loop),

depending on the operating condition. The three con-

trol 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 different control loops (see the

Compensation section). The CCS and CCI loops are

compensated internally, and the CC loop is compen-

sated externally.

Continuous-Conduction Mode

With sufficiently large charge current, the MAX17005B/

MAX17006B/MAX17015Bs’ inductor current never

crosses zero, which is defined as continuous-conduc-

tion 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

comparator output goes high and the controller initiates

the off-time by turning off the high-side MOSFET and

turning on the low-side MOSFET. The operating fre-

quency is governed by the off-time and is dependent

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

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

the 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. ZCMP causes the MAX17005B/MAX17006B/

MAX17015B to enter into the discontinuous conduction

mode (see the

Discontinuous Conduction section).

Discontinuous Conduction

The MAX17005B/MAX17006B/MAX17015B can also

operate in discontinuous conduction mode to ensure that

the inductor current is always positive. The MAX17005B/

MAX17006B/MAX17015B enter discontinuous conduction

mode when the output of the LVC control point falls below

Ω, 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.

For CC compensation, connect a 0.01μF capacitor at

CC. The crossover frequency occurs at:

where:

fGM

G

k

C

CO CV

OUT

MV

OUT

_

.

=×

×

×

17

2

Ω

π

f

tt

SW

ON

OFF

=

+

1

I

Vt

L

RIPPLE

BATT

OFF

=

×

t

LI

VV

ON

RIPPLE

DCIN

BATT

=

×

-