MAX713CSE(2002) データシートの表示（PDF） - Maxim Integrated

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MAX713CSE
(Rev.:2002)

NiCd/NiMH Battery Fast-Charge Controllers

Maxim Integrated 

NiCd/NiMH Battery

Fast-Charge Controllers

Table 5. Trickle-Charge Current

Determination from PGM3

PGM3

V+

OPEN

REF

BATT-

FAST-CHARGE

RATE

4C

2C

C

C/2

TRICKLE-CHARGE

CURRENT (ITRICKLE)

IFAST/64

IFAST/32

IFAST/16

IFAST/8

Q1

DC IN

DRV

MAX712

MAX713 FASTCHG

V+

10k

10k

D1

R7

BATTERY

Q2

The MAX712/MAX713 internally set the trickle-charge

current by increasing the current amplifier gain (Figure

6), which adjusts the voltage across RSENSE (see

Trickle-Charge VSENSE in the Electrical Characteristics

table).

Configuration:

Nonstandard Trickle-Charge

Current Example

Typical Operating Circuit

2 x Panasonic P-50AA 500mAh AA NiCd batteries

C/3 fast-charge rate

264-minute timeout

Negative voltage-slope cutoff enabled

Minimum DC IN voltage of 6V

Settings:

Use MAX713

PGM0 = V+, PGM1 = open, PGM2 = BATT-,

PGM3 = BATT-, RSENSE = 1.5Ω (fast-charge current,

IFAST = 167mA), R1 = (6V - 5V) / 5mA = 200Ω

Since PGM3 = BATT-, the voltage on RSENSE is regulat-

ed to 31.3mV during trickle charge, and the current is

20.7mA. Thus the trickle current is actually C/25, not

C/16.

Further Reduction of Trickle-Charge

Current for NiMH Batteries

The trickle-charge current can be reduced to less than

C/16 using the circuit in Figure 7. In trickle charge,

some of the current will be shunted around the battery,

since Q2 is turned on. Select the value of R7 as follows:

R7 = (VBATT + 0.4V) / (lTRlCKLE - IBATT)

where

VBATT = battery voltage when charged

ITRlCKLE = MAX712/MAX713 trickle-charge

current setting

IBATT = desired battery trickle-charge current

RSENSE

GND

Figure 7. Reduction of Trickle Current for NiMH Batteries

(Linear Mode)

Regulation Loop

The regulation loop controls the output voltage between

the BATT+ and BATT- terminals and the current

through the battery via the voltage between BATT- and

GND. The sink current from DRV is reduced when the

output voltage exceeds the number of cells times

VLIMIT, or when the battery current exceeds the pro-

grammed charging current.

For a linear-mode circuit, this loop provides the following

functions:

1) When the charger is powered, the battery can be

removed without interrupting power to the load.

2) If the load is connected as shown in the Typical

Operating Circuit, the battery current is regulated

regardless of the load current (provided the input

power source can supply both).

Voltage Loop

The voltage loop sets the maximum output voltage

between BATT+ and BATT-. If VLIMIT is set to less than

2.5V, then:

Maximum BATT+ voltage (referred to BATT-) = VLIMIT x

(number of cells as determined by PGM0, PGM1)

VLIMIT should be set between 1.9V and 2.5V. If VLIMIT

is set below the maximum cell voltage, proper

termination of the fast-charge cycle might not occur.

Cell voltage can approach 1.9V/cell, under fast charge,

in some battery packs. Tie VLIMIT to VREF for normal

operation .

With the battery removed, the MAX712/MAX713 do not

provide constant current; they regulate BATT+ to the

maximum voltage as determined above.

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