LTC4156IUFD View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC4156IUFD

Dual-Input Power Manager/3.5A LiFePO4 Battery Charger with I2C Control and USB OTG

Linear Technology 

LTC4156

APPLICATIONS INFORMATION

Alternate Input Power Configurations

For applications requiring only a single input, the external

circuit required for overvoltage protection is considerably

simplified. Only a single N-channel MOSFET and resistor

are required for positive voltage protection, as shown in

Figure 11, and OVGCAP may be left unconnected. Applica-

tions using the USB On-The-Go step-up regulator should

connect R1 to USBSNS and the gate of MN1 to USBGT.

Applications not using USB On-The-Go may use either the

USBSNS/USBGT pins or the WALLSNS/WALLGT pins. The

unused pins may be left unconnected.

For dual-input applications requiring reverse-voltage

protection, no additional power transistors are required.

The circuit in Figure 12 provides positive protection up to

the drain breakdown voltage rating of MN3 and MN4 and

negative protection down to the drain breakdown volt-

age rating of MN1 and MN2. Q1 and Q2 are small-signal

transistors to protect the gate oxides of MN1 and MN2.

Note that it is necessary to orient the N-channel MOSFETs

with the drain connections common and the source/body

connections to the input connector and the VBUS pin.

Choosing the Inductor

The LTC4156 is designed to operate with a 1µH inductor,

with core saturation, winding resistance, and thermal

rise characteristics appropriate for the application’s peak

currents. The inductor current ripple magnitude is ap-

proximately 400mA under normal conditions, resulting

in a peak inductor current 200mA higher than the aver-

age output current of the switching regulator. The aver-

age output current of the step-down regulator is higher

than the average input current by the ratio VBUS/VOUT,

neglecting efficiency losses. The LTC4156 can tolerate

transient excursions beyond the inductor’s core saturation

level, but the inductor current will increase rapidly to the

LTC4156’s peak current clamp as incremental inductance

tends toward zero. If an overload condition persists with

a small inductor, it is possible that the inductor could be

damaged by its own resistive temperature rise.

TO POWER

MN1

INPUT

WALLSNS

WALLGT

LTC4156

VBUS

USBGT

R1

USBSNS

OVGCAP

4156 F11

Figure 11. Single-Input Overvoltage Protection

TO WALL

INPUT

TO USB

INPUT

R5

Q3 Q1 47k

R3 5M

R1 3.6k

WALLSNS

WALLGT

MN1

MN3

MN2

MN4

LTC4156

VBUS

R4 5M

Q4

Q2 R6

47k

R2 3.6k

USBGT

USBSNS

OVGCAP

C1

OPT

0.01µF

4156 F12

Figure 12. Dual-Input Positive and Negative Voltage Protection

4156f

43

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