PS No. 6194-7/7

LB1939T

This catalog provides information as of February, 2004. Specifications and information herein are subject

to change without notice.

Specifications of any and all SANYO products described or contained herein stipulate the performance,

characteristics, and functions of the described products in the independent state, and are not guarantees

of the performance, characteristics, and functions of the described products as mounted in the customer’s

products or equipment. To verify symptoms and states that cannot be evaluated in an independent device,

the customer should always evaluate and test devices mounted in the customer’s products or equipment.

SANYO Electric Co., Ltd. strives to supply high-quality high-reliability products. However, any and all

semiconductor products fail with some probability. It is possible that these probabilistic failures could

give rise to accidents or events that could endanger human lives, that could give rise to smoke or fire,

or that could cause damage to other property. When designing equipment, adopt safety measures so

that these kinds of accidents or events cannot occur. Such measures include but are not limited to protective

circuits and error prevention circuits for safe design, redundant design, and structural design.

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Any and all information described or contained herein are subject to change without notice due to

product/technology improvement, etc. When designing equipment, refer to the “Delivery Specification”

for the SANYO product that you intend to use.

Information (including circuit diagrams and circuit parameters) herein is for example only; it is not

guaranteed for volume production. SANYO believes information herein is accurate and reliable, but

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Constant Current Control Usage Notes

This IC supports both constant current control and constant voltage control modes. However, since both of these control

circuits operate at all times, certain of the limitations imposed by the constant voltage control circuit apply may when

using constant current control.

For example, if constant current control is used with the application circuit shown in figure 2, if VC = 0.9 V (= Vref) and

RFB = 1

Ω, then the output current can be calculated as follows from (1) on the previous page.

Iout = (0.9/4.5 + 0.03) / (1 + 0.1)

= 0.23/1.1

≈ 0.209A

Here, if the value driven load resistance RL is r, since the RFG pin voltage is 0.23 V and the npn transistor output

saturation voltage is 0.1 V (typical), the pnp transistor output pin voltage can be calculated as follows.

Vout = (RFG pin voltage) + (npn transistor output saturation voltage) + (voltage across the load terminals)

= 0.23 + 0.1 + 0.209

× r

= 0.3 + 0.209r

At the same time, however, this IC’s internal constant voltage control circuit controls the output voltage as follows.

Vout' = VC

× 1.95 ≈ 1.75 V

Therefore, it will not be possible to use the constant current control mode if the value of r is set so that Vout is greater

than Vout'. That is, the condition

0.33 + 0.209r > 1.75

implies that

r > 6.79

This means that constant current control can be used when the value of the load resistance used is strictly less than 6.79

Ω.