LTC4160 datasheet(21/32 Pages) LINER

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LTC4160/LTC4160-1

41601f

APPLICATIONS INFORMATION

Bidirectional PowerPath Switching Regulator CLPROG

Resistor and Capacitor Selection

As described in the Bidirectional PowerPath Switching

Regulator – Step-Down Mode section, the resistor on the

CLPROG pin determines the average VBUS input current

limit. In step-down mode the switching regulator’s VBUS

input current limit can be set to either the 1x mode (USB

100mA), the 5x mode (USB 500mA) or the 10x mode. The

VBUS input current will be comprised of two components,

the current that is used to drive VOUT and the quiescent

current of the switching regulator. To ensure that the total

average input current remains below the USB speciﬁcation,

both components of input current should be considered.

The Electrical Characteristics table gives the typical values

for quiescent currents in all settings as well as current limit

programming accuracy. To get as close to the 500mA or

100mA speciﬁcations as possible, a precision resistor

should be used. Recall that:

IVBUS = IVBUSQ + VCLPROG/RCLPPROG • (hCLPROG +1).

An averaging capacitor is required in parallel with the

resistor so that the switching regulator can determine the

average input current. This capacitor also provides the

dominant pole for the feedback loop when current limit

is reached. To ensure stability, the capacitor on CLPROG

should be 0.1μF or larger.

Bidirectional PowerPath Switching Regulator Inductor

Selection

Because the VBUS voltage range and VOUT voltage range

of the PowerPath switching regulator are both fairly nar-

row, the LTC4160/LTC4160-1 were designed for a speciﬁc

inductance value of 3.3μH. Some inductors which may be

suitable for this application are listed in Table 3.

Table 3. Recommended PowerPath Inductors for the

LTC4160/LTC4160-1

INDUCTOR

TYPE

(μH)

MAX IDC

(A)

MAX DCR

(Ω)

SIZE IN mm

(L x W x H) MANUFACTURER

LPS4018

3.3

2.2

0.08

3.9 x 3.9 x 1.7 Coilcraft

www.coilcraft.com

D53LC

DB318C

3.3

2.26

1.55

0.034

0.070

5 x 5 x 3

3.8 x 3.8 x 1.8

Toko

www.toko.com

WE-TPC

Type M1

3.3

1.95

0.065

4.8 x 4.8 x 1.8 Wurth Electronik

www.we-online.com

CDRH6D12

CDRH6D38

3.3

2.2

3.5

0.063

0.020

6.7 x 6.7 x 1.5

7 x 7 x 4

Sumida

www.sumida.com

Bidirectional PowerPath Switching Regulator VBUS

and VOUT Bypass Capacitor Selection

The type and value of capacitors used with the LTC4160/

LTC4160-1 determine several important parameters such

as regulator control-loop stability and input voltage ripple.

Because the LTC4160/LTC4160-1 use a bidirectional

switching regulator between VBUS and VOUT, the VBUS

current waveform contains high frequency components.

It is strongly recommended that a low equivalent series

resistance (ESR) multilayer ceramic capacitor (MLCC) be

used to bypass VBUS. Tantalum and aluminum capacitors

are not recommended because of their high ESR. The value

of the capacitor on VBUS directly controls the amount of

input ripple for a given load current. Increasing the size

of this capacitor will reduce the input ripple.

The inrush current limit speciﬁcation for USB devices is

calculated in terms of the total number of Coulombs needed

to charge the VBUS bypass capacitor to 5V. The maximum

inrush charge for USB On-The-Go devices is 33μC. This

places a limit of 6.5μF of capacitance on VBUS assuming

a linear capacitor. However, most ceramic capacitors have

a capacitance that varies with bias voltage. The average

capacitance needs to be less than 6.5μF over a 0V to 5V bias

voltage range to meet the inrush current-limit speciﬁcation.

A 10μF capacitor in a 0805 package, such as the Murata

GRM21BR71A106KE51L would be a suitable VBUS bypass

capacitor. If more capacitance is required for better noise

performance and stability, it should be connected directly

to the VBUS pin when using the overvoltage protection

circuit. This extra capacitance will be soft-connected over

a couple of milliseconds to limit inrush current and avoid

excessive transient voltage drops on VBUS.

To prevent large VOUT voltage steps during transient load

conditions, it is also recommended that an MLCC be used

to bypass VOUT. The output capacitor is used in the com-

pensation of the switching regulator. At least 10μF with

low ESR are required on VOUT. Additional capacitance will

improve load transient performance and stability.

MLCCs typically have exceptional ESR performance.

MLCCs combined with a tight board layout and an unbroken

ground plane will yield very good performance and low

EMI emissions.

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