ZLED7025 datasheet(14/26 Pages) IDT

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ZSLS7025 Datasheet

April 20, 2016

AVG

PEAK

TOFF

MIN

OFF

−

In general, setting the peak inductor current to 1.5 times the average input current is sufficient to maintain good

regulation of the output current.

(6)

Where

VCS_TH = VADJ/10 if 0.5V < VADJ

≤ 2.4V or

VCS_TH = 0.24V if VADJ > 2.4V or if the ADJ pin is floating

2.8

Setting the Minimum Off-Time tOFF_MIN

The ZSLS7025 operates in a pulsed frequency modulation (PFM) mode. In nominal operation, on-time and off-time

are determined according to equations (8), (9), (10), and (11). In most applications, the recommended value for

tOFF_MIN is 1µs. The relationship between tOFF_MIN and RTOFF is shown in equation (7) and Where tOFF_MIN is in µs and

RTOFF is in

Ω.

Figure 2.5. tOFF_MIN is valid as long as VFB has not reached the threshold of 300 mV.

(7)

Where tOFF_MIN is in µs and RTOFF is in

Ω.

Figure 2.5

Minimum Off-Time tOFF_MIN vs. RTOFF

2.9

Switching Frequency and Inductor Value

The inductance value of the inductor (L1) directly determines the switching frequency of the converter. Under fixed

conditions, the inductance is inversely proportional to the switching frequency; i.e., the larger the inductance, the

lower the switching frequency. A higher switching frequency will reduce the value required for the inductor but will

increase the switching loss in the external MOSFET, Q1 (see section 2.4).

RTOFF Value in k

Ω

Minimum tOFF_MIN is 1µs →

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