TK65428MTL/428 查看數據表（PDF） - Toko America Inc

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TK65428MTL/428

STEP-DOWN CONVERTER WITH BATTERY MONITOR

Toko America Inc  

TK654xx

ADVANCED INFORMATION

DESIGN CONSIDERATIONS (CONT.)

The thresholds for the Low Battery Input (LBI) and the turnoff (VOFF) can be set independently using a single resistive

divider. Equations and a chart for selecting the LBI and VOFF thresholds are provided below:

LBI threshold = 1.22 V X (R1 + R2) / R2

VOFF threshold = LBI threshold - 720 nA X R1

4.0 V

LBI THRESHOLD

3.5 V

VOFF THRESHOLD (R1 = 243 K)

3.0 V

2.5 V

(R1 = 487 K)

(R1 = 732 K)

(R1 = 976 K)

2.0 V

0.6 1.0 1.4 1.8

RATIO OF R1/R2

DROPOUT CHARACTERISTICS

In battery powered applications, the input supply is not typically a constant value. As the battery discharges, the input

voltage will approach the output voltage. As the voltage on the input of the converter drops, the following two

characteristics can be observed: (a) as the battery voltage drops, output ripple will increase, (b) at very low battery levels

and high current loads, the output voltage may drop significantly below the regulation threshold.

In some applications, the above characteristics may not present a problem. For those applications that may be sensitive

to these characteristics, the LBO output can provide an early warning system indicating that battery failure is near. As

the battery voltage continues to drop, the turnoff feature of the TK654xx will ultimately turn the converter off (see LBI

Indicator section).

Page 14

September 1999 TOKO, Inc.

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