LTC4162EUFD-FST#PBF datasheet(34/52 Pages) AD

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LTC4162-F

Rev A

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APPLICATIONS INFORMATION

with a 10μF capacitor. Also shown is the troublesome

constant-currentregionwheretheimpedanceisessentially

that of just the 10μF bypass capacitor. Two other networks

areshowncomprisingalarger100μFand1000μFcapacitor

bothinserieswitha2.5Ωresistorforimpedanceflattening

and phase shift mitigation. The compensation capacitor

should be a solid or "polymer" electrolytic type such as the

Panasonic ZA hybrid series to preserve stable ESR over

temperature.Conventional,or"wet",electrolyticcapacitors

should be avoided as their ESR increases dramatically at

low temperature. The larger compensation capacitor will

create a wider impedance flattening frequency range and

therefore more stable operation.

0.01

0.1

100

FREQUENCY (kHZ)

0.1

100

1000

10000

4162F F09

10µF||2.5

(Low Impedance)

10µF||2.5

(Low Impedance)

10µF||2.5

(Low Impedance)

10µF||2.5

(LOW IMPEDANCE)

10µF

(High Impedance)

10µF

(High Impedance)

10µF

(High Impedance)

10µF

(HIGH IMPEDANCE)

10µF||(1000µF + 2.5)

10µF||(100µF + 2.5)

Figure 9. Aggregate Input Impedance vs Frequency

USB Power Delivery

For 1 to 4 cell Lithium-Ion products, the LTC4162 can sup-

port the USB Power Delivery specification. Table 7 shows

the relevant compatibility of cell_count vs USB profile.

Table 7. Cell Count Support vs USB Power Delivery Profile

USB PD

Profile

1 Cell

Product

2 Cell

Product

3 Cell

Product

4 Cell

Product

5 Cell

Product

✔

✘

✔

✘

15V

✔

✘

20V

✔

Battery and Input Voltage Hot Plugging

Aluminum-polymer, aluminum-electrolytic or tantalum

capacitors can minimize overshoot when hot plugging

a battery or power connector. Ceramic capacitors are

required close to the LTC4162 VOUT pins to supply very

high frequency switching current but their extreme non-

linearity produces excessively high overshoot during hot

plug. Their capacitance typically plunges by more than

80% as the voltage increases from 0V to rated voltage.

This nonlinearity encourages high current at low voltage

while rapidly shedding capacitance as the voltage rises; a

dangerouscombinationresultinginhighvoltageovershoot.

Empirically, the combination of a ceramic capacitor near

the LTC4162 and a lower Q, voltage-stable, aluminum

type capacitor provides the most robust combination.

TVS diodes may also be used to limit voltage overshoot

on either the input connector or the battery connector

of a portable product. A single protection device (lossy

capacitor or TVS) on the VOUT terminal may be sufficient

to handle hot plug events from either the battery or the

input connector as the power path MOSFETs diode-OR

to the VOUT node. For solar panel applications the solar

panel compensation network may provide adequate hot

plugprotectionontheinputterminal.SeeApplicationNote

AN88 for examples.

Printed Circuit Board Layout Considerations

The Exposed Pad on the backside of the LTC4162 must

be securely soldered to the PC board ground. It serves

as the analog ground pin and thermal sink. There should

be a group of vias under the grounded backside leading

directly down to an internal unbroken ground plane.

High frequency currents tend to find their way on the

ground plane along a mirror path directly beneath the

incident path on the top of the board. If there are slits or

cuts in the ground plane due to other traces on that layer,

the current will be forced to go around the slits. If high

frequency currents are not allowed to flow back through

their natural, least-area, path, excessive voltage will build

up and radiated emissions will occur (see Figure 10). To

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