LTC4098EUDC-1 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC4098EUDC-1

USB Compatible Switching Power Managers/Li-Ion Chargers with Overvoltage Protection

Linear Technology 

LTC4098/LTC4098-1

APPLICATIONS INFORMATION

is used in the compensation of the switching regulator. At

least 10μF with low ESR are required on VOUT. Additional

capacitance will improve load transient performance

and stability.

Multilayer ceramic chip capacitors typically have excep-

tional ESR performance. MLCCs combined with a tight

board layout and an unbroken ground plane will yield very

good performance and low EMI emissions.

There are several types of ceramic capacitors avail-

able each having considerably different characteristics.

For example, X7R ceramic capacitors have the best voltage

and temperature stability. X5R ceramic capacitors have

apparently higher packing density but poorer performance

over their rated voltage and temperature ranges. Y5V

ceramic capacitors have the highest packing density,

but must be used with caution, because of their extreme

nonlinear characteristic of capacitance versus voltage. The

actual in-circuit capacitance of a ceramic capacitor should

be measured with a small AC signal and DC bias as is

expected in-circuit. Many vendors specify the capacitance

versus voltage with a 1VRMS AC test signal and, as a result,

over state the capacitance that the capacitor will present

in the application. Using similar operating conditions as

the application, the user must measure or request from

the vendor the actual capacitance to determine if the

selected capacitor meets the minimum capacitance that

the application requires.

Overprogramming the Battery Charger

The USB high power specification allows for up to 2.5W

to be drawn from the USB port. The switching regulator

transforms the voltage at VBUS to just above the voltage

at BAT with high efficiency, while limiting power to less

than the amount programmed at CLPROG. The charger

should be programmed (with the PROG pin) to deliver the

maximum safe charging current without regard to the USB

specifications. If there is insufficient current available to

charge the battery at the programmed rate, it will reduce

charge current until the system load on VOUT is satisfied

and the VBUS current limit is satisfied. Programming the

charger for more current than is available will not cause

the average input current limit to be violated. It will merely

allow the battery charger to make use of all available

power to charge the battery as quickly as possible, and

with minimal power dissipation within the charger.

Overvoltage Protection

It is possible to protect both VBUS and WALL from over-

voltage damage with several additional components, as

shown in Figure 7. Schottky diodes D1 and D2 pass the

larger of V1 and V2 to R1 and OVSENS. If either V1 or V2

exceeds 6V plus VF(SCHOTTKY), OVGATE will be pulled to

GND and both the WALL and USB inputs will be protected.

Each input is protected up to the drain-source breakdown,

BVDSS, of MN1 and MN2. R1 must also be rated for the

power dissipated during maximum overvoltage. See the

Operations section for an explanation of this calculation.

Table 4 shows some N-channel MOSFETs that may be

suitable for overvoltage protection.

Table 4. Recommended OVP FETs

N-CHANNEL

MOSFET

BVDSS

Si2302ADS

20V

IRLML2502

20V

Si1472DH

30V

NTLJS4114N

30V

RON

70mΩ

35mΩ

65mΩ

20mΩ

FDN372S

30V

45mΩ

PACKAGE

SOT-23

SOT-23

SC70-6

2mm × 2mm

DFN

SOT-23

MN1

V1

WALL

V2

D2

D1 MN2

OVGATE

LTC4098/

LTC4098-1

VBUS

C1

R1

OVSENS

40981 F07

Figure 7. Dual Input Overvoltage Protection

40981fc

23

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