DS2715 查看數據表（PDF） - Maxim Integrated

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DS2715

NiMH Battery Pack Charge Controller

Maxim Integrated 

DS2715: NiMH Battery Pack Charge Controller

The RT resistor (R5) is set to 47kΩ for a timeout of 70 minutes. This would be appropriate for cells with a capacity

of about 1Ah when charged with the 1.07A charge current. The resistor divider with R12 and R13 is configured to

present the voltage equivalent to a single cell on the Vbatt pin.

The value of L1 in the example represents a moderate switching speed of 100-150khz for fast-charge mode. L1

may be adjusted to fit specific application goals as long as the associated change in switching speed does not

exceed the circuit’s ability to maintain proper regulation of the sense resistor voltage. Since TOPOFF and

PRECHARGE modes have a faster switching frequency than FAST-CHARGE, the regulation in these modes must

be considered.

All capacitors should be ceramic surface mount types of good quality where possible. The 47uF capacitor may be

any type that meets the application requirements. A different network for C1 and C2 may be necessary depending

on the types of capacitors used, the layout, and the transient requirements of the application load. All resistors not

previously mentioned are standard surface mount types.

Linear

Figure 6 shows a typical application circuit for charging a 3-cell stack in linear mode. The Mode pin is tied to VSS for

linear operation. A 250mΩ sense resistor (R7) sets the charge current to .484A, which the DS2715 regulates by

controlling the VGS of Q1 through the bias resistor R3. The bias resistor should be chosen so that the current that

VCH is required to sink does not exceed 20mA when VCH is fully turned on. The preferred design target for FAST-

CHARGE conditions is 10mA. The RC network of R3 and C5 set a pole in the control loop to ensure stability.

Figure 6. TYPICAL Linear APPLICATION CIRCUIT FOR A 3-CELL STACK

+6VDC

D1

B340A-13

LOAD

D2 R2 220

R1

150

C1 C2

47 uF 1 uF

C3

.1 uF

Q2

2N7002

C5 4.7 uF

Q1

IRF9Z24

LED1 R3 470

U1

R4 470

LED1

Vdd

Rt

DS2715

Vch Vbatt

Div

R5 86K

R10

SNS+

10K

Cbias

Mode

THM

VSS CTG SNS-

R8

10k

C4

0.1 uF

R12

200K

R13

100K

THM1

10K

R7 0.25

A lower charge current is used for linear mode, in addition to a lower supply voltage. This reduces the power

dissipation of Q1 to a manageable level. This dissipation must be closely considered in the application and proper

heatsinking precautions must be taken. Different transistors may be selected for Q1 based on package size and

thermal requirements. An 86kΩ resistor on RT (R5) sets the FAST-CHARGE timeout to about 129 minutes, which

for the given charge rate is appropriate for cells of about .9Ah capacity. The other aspects of the circuit are

equivalent to those of the switchmode circuit.

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