ISL9120 datasheet(9/13 Pages) RENESAS | Compact High Efficiency Low Power Buck-Boost Regulator

9 / 13 page

ISL9120

FN8659 Rev.2.00

Page 9 of 13

May 23, 2017

Variable Peak Current Limit Scheme

To optimize efficiency across the output current range, the ISL9120

implements a multilevel current limit scheme with 32 levels

between 350mA and 2A. The transition from one level to the other

is determined by the number of pulses in a PFM burst (pulse count)

as shown in Figure 16. At a given peak current limit level, the pulse

count increases as the output current increases. When the pulse

count reaches the upper threshold at the existing current limit, the

current limit will switch to the next higher level. Similarly, if the pulse

count reaches the lower threshold at the existing current limit, the

device will switch to the next lower level of peak current limit. If the

pulse count reaches the upper threshold at the highest current limit,

the current limit will not rise any further. Increasing the output

current beyond this point may cause the output to lose voltage

regulation.

FIGURE 15. PFM MODE OPERATION CONCEPT

FIGURE 16. PEAK CURRENT LIMIT STEP UP TRANSITION

VOUT

1.015 * VOUT_NOMINAL

VOUT_NOMINAL

PEAK CURRENT LIMIT

IOUT

IPK_LMT2

IPK_LMT1

INCREASING IOUT

tMIN

ISL9120 Datasheet(PDF) 9 Page - Renesas Technology Corp