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LM3151, LM3152, LM3153

SNVS562G – SEPTEMBER 2008 – REVISED MARCH 2011

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Table 1. Inductor Selection Table (continued)

Inductor Designator

Inductance (µH)

Current (A)

Part Name

Vendor

L48

0.33

15-

4. Determine Output Capacitance

Typical hysteretic COT converters similar to the LM3151/2/3 require a certain amount of ripple that is generated

across the ESR of the output capacitor and fed back to the error comparator. Emulated Ripple Mode control built

into the LM3151/2/3 will recreate a similar ripple signal and thus the requirement for output capacitor ESR will

decrease compared to a typical Hysteretic COT converter. The emulated ripple is generated by sensing the

voltage signal across the low-side FET and is then compared to the FB voltage at the error comparator input to

determine when to initiate the next on-time period.

(1)

The maximum ESR allowed to prevent over-voltage protection during normal operation is:

The minimum ESR must meet both of the following criteria:

Any additional parallel capacitors should be chosen so that their effective impedance will not negatively attenuate

the output ripple voltage.

5. MOSFET Selection

The gate drive current from VCC must not exceed the minimum current limit of VCC. The drive current from VCC

can be calculated with:

where

•

where

•

14

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