LMZ22010 datasheet(21/36 Pages) TI1

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COUTJ

(0.165V - 9A x 0.003) x (

)

350e3

3.3V

J615 2F

Istep

COUTJ

(VOUT - ISTEP x ESR) x (

)

fSW

VOUT

1.07k

Rfbb

2.26k

Rfbt

107

Rtkb

226

Rtkt

3.3V Master

2.5Vout

50 2A

Int VCC

LMZ22010

www.ti.com

SNVS687H – MARCH 2011 – REVISED AUGUST 2015

divider resistors is the same as the ratio of the output voltage setting divider. Proper operation in tracking mode

dictates the soft-start time of the slave rail be shorter than the master rail; a condition that is easy to satisfy

because the CSS cap is replaced by RTKB. The tracking function is only supported for the power up interval of the

master supply; once the SS/TRK rises past 0.795 V the input is no longer enabled and the 50-µA internal current

source is switched off.

Figure 52. Tracking Option Input Detail

8.2.2.6 COUT Selection

None of the required COUT output capacitance is contained within the module. A minimum value ranging from 330

μF for 6-VOUT to 660 μF for 1.2-VOUT applications is required based on the values of internal compensation in the

error amplifier. These minimum values can be decreased if the effective capacitor ESR is higher than 15 m

Ω.

A Low ESR (15 m

Ω) tantalum, organic semiconductor or specialty polymer capacitor types in parallel with a 47-

nF X7R ceramic capacitor for high-frequency noise reduction is recommended for obtaining lowest ripple. The

output capacitor COUT may consist of several capacitors in parallel placed in close proximity to the module. The

output voltage ripple of the module depends on the equivalent series resistance (ESR) of the capacitor bank, and

can be calculated by multiplying the ripple current of the module by the effective impedance of your chosen

output capacitors. Electrolytic capacitors will have large ESR and lead to larger output ripple than ceramic or

polymer types. For this reason a combination of ceramic and polymer capacitors is recommended for low output

ripple performance.

The output capacitor assembly must also meet the worst case ripple current rating of

ΔiL, as calculated in

Equation 8. Loop response verification is also valuable to confirm closed loop behavior.

For applications with dynamic load steps; the following equation provides a good first pass approximation of COUT

for load transient requirements.

(8)

For 12 VIN, 3.3 VOUT, a transient voltage of 5% of VOUT = 0.165 V (ΔVOUT), a 9A load step (ISTEP), an output

capacitor effective ESR of 3 m

Ω, and a switching frequency of 350kHz (fSW):

(9)

NOTE

The stability requirement for minimum output capacitance must always be met.

One recommended output capacitor combination is two 330-

μF, 15-mΩ ESR tantalum polymer capacitors

connected in parallel with a 47-µF 6.3-V X5R ceramic. This combination provides excellent performance that may

exceed the requirements of certain applications. Additionally some small 47-nF ceramic capacitors can be used

for high-frequency EMI suppression.

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