CDH2D09 datasheet(32/44 Pages) MAXIM

32 / 44 page

PMIC with Integrated Charger and

Smart Power Selector for Handheld Devices

______________________________________________________________________________________

Determine ICHGMAX by considering the characteristics

of the battery. It is not necessary to limit the charge cur-

rent based on the capabilities of the expected AC-to-

DC adapter or USB charging input, the system load, or

thermal limitations of the PCB. The MAX8671X automat-

ically lowers the charging current as necessary to

accommodate these factors.

For the selected value of RCISET, calculate ICHGMAX,

IPQ, and ITO as follows:

In addition to setting the charge current, CISET also pro-

vides a means to monitor battery charge current. The

CISET output voltage tracks the charge current delivered

to the battery, and can be used to monitor the charge

rate, as shown in Figure 9. A 1.5V output indicates the

battery is being charged at the maximum set fast-charge

current, and 0V indicates no charging. This voltage is

also used by the charger control circuitry to set and

monitor the battery current. Avoid adding capacitance

directly to the CISET pin that exceeds 10pF. If filtering of

the charge current monitor is necessary, include a resis-

tor of 100k

Ω or more between CISET and the filter

capacitor to preserve charger stability.

Step-Down Converters

(REG1, REG2, REG3)

REG1, REG2, and REG3 are high-efficiency 2MHz cur-

rent-mode, step-down converters with adjustable out-

puts. Each REG1, REG2, and REG3 step-down

converter delivers at least 425mA.

The step-down regulator power inputs (PV_) must be

connected to SYS. The step-down regulators operate

with VSYS from 2.6V to 5.5V. Undervoltage lockout

ensures that the step-down regulators do not operate

with SYS below 2.6V (typ).

See the

Enable/Disable (EN) and Sequencing section

for how to enable and disable the step-down convert-

ers. When enabled, the MAX8671X gradually ramps

each output up during a soft-start time. Soft-start elimi-

nates input current surges when regulators are

enabled.

See the

PWM section for information about the step-

down converters control scheme.

CHGMAX

CISET

CHGMAX

=×

2000

MONITORING THE BATTERY CHARGE

CURRENT WITH VCISET

BATTERY CHARGING CURRENT (A)

DISCHARGING

1.5

RCISET

2000

x IBAT

VCISET =

2000

1.5V

RCISET

Figure 9. Monitoring the Battery Charge Current with the

Voltage from CISET to AGND

RCISET (k

Ω)ICHGMAX (mA)

IPQ (mA)

ITO (mA)

3.01

1000

100

4.02

746

4.99

601

6.04

497

6.98

430

8.06

372

9.09

330

10.0

300

11.0

273

12.1

248

13.0

231

14.0

214

15.0

200

Table 5. Ideal Charge Currents vs.

Charge Setting Resistor

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