DS2711/DS2712: Loose-Cell NiMH Chargers

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Undervoltage Lockout (UVLO)

machine is forced to the RESET state, and all charge timers are reset. A 10

µs deglitch circuit provides noise

immunity.

Internal Oscillator and Clock Generation

An internal oscillator provides the main clock source used to generate timing signals for internal chip operation. The

precharge timer, hold-off timers, and timings for CC1/CC2 operation and cell testing are derived from this timebase.

Current-Sense Amplifier (DS2711)

An error amplifier block provides several options to regulate the charge current. The 20mA open-drain output can

drive a PMOS or PNP pass element for linear regulation, or the output can drive an optocoupler for isolated

feedback to a primary-side PWM controller. The VN0 pin is a remote-sense return and should be connected to the

grounded side of the sense resistor using a separate, insulated conductor.

Figure 6. Current-Sense Amplifier Response

the current-sense signal (across a sense resistor) and the 0.125V internal reference is produced so the voltage

Current-Sense Comparator (DS2712)

The comparator in the DS2712 switches between ON and OFF and is capable of driving a PNP bipolar or a PMOS

transistor, enabling the use of a switched-mode power stage. Hysteresis on the comparator input provides noise

rejection. In the closed-loop regulation circuit of Figure 5, the comparator regulates voltage across the sense

resistor to a DC average of:

Frequency (Hertz)

10

1

10

2

10

3

10

4

10

5

10

6

10

7

0.00

0.20

0.40

0.60

0.80

1.00

1.20

-300

-250

-200

-150

-100

-50

0

Gain

Phase