SC810 datasheet(16/19 Pages) SEMTECH

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SC810

A short to ground on the IPRGM current programming pin

will prevent startup. During charging, a short to ground

applied to the IPRGM pin forces the SC810 into reset,

turning off the output and holding it off until the short is

removed. When the IPRGM short to ground is removed,

the charger begins normal operation automatically

without input power cycling.

Over-Current Protection

Over-current protection is provided in all modes of opera-

tion, including CV regulation. The output current is limited

to either the programmed pre-charge current limit value

or the fast-charge current limit value, depending on the

voltage at the output.

Input Over-Voltage Protection

The VIN pin is protected from over-voltage to at least 30V

above GND. When the input voltage exceeds the Over-

Voltage Protection (OVP) rising threshold ( VT

OVP-R

charging is halted. When the input voltage falls below the

OVP falling threshold (VT

OVP-F

), charging resumes. An OVP

fault turns off the STATB output. STATB is turned on again

when charging restarts.

The OVP threshold has been set relatively high to permit

the use of poorly regulated adapters. Such adapters may

output a high voltage until loaded by the charger. A

too-low OVP threshold could prevent the charger from

ever turning on and loading the adapter to a lower voltage.

If the adapter voltage remains high despite the charging

load, the fast thermal limiting feature will immediately

reduce the charging current to prevent overheating of the

SC810. This behavior is illustrated in Figure 4, in which V

BAT

= 3.0V, I

= 700mA, and V

VIN

is stepped from 0V to 8.1V.

Initially, power dissipation in the SC820 is 3.6W.

Notice the BAT output current is rapidly reduced to limit

the internal die temperature, then continues to decline as

the circuit board gradually heats up, further reducing the

conduction of heat from the die to the ambient environ-

ment. The fast thermal limiting feature ensures compliance

with CCSA YD/T 1591-2006, Telecommunication Industrial

Standard of the People’s Republic of China — Technical

Requirements and Test Method of Charger and Interface for

Mobile Telecommunication Terminal, Section 4.2.3.1.

1s/div

VIN

(2V/div)

VIN

BAT

=0V—

BAT

(100mA/div)

BAT

=0mA—

VIN

=8.1V, V

BAT

=3.0V

BAT

=700mA (Initially), P

DISSIPATION

=3.6W (Initially)

BAT

(2V/div)

Figure 4 — Thermal Limiting Example

Operation Without a Battery

The SC810 can be operated as a 4.2V LDO regulator

without the battery present, for example, factory testing.

If this use is anticipated, the output capacitance C

BAT

should be at least 2.2μF to ensure stability. To operate the

charger without a battery, the ENB pin must be driven low

or grounded.

Capacitor Selection

Low cost, low ESR ceramic capacitors such as the X5R and

X7R dielectric material types are recommended. The BAT

pin capacitor, C

BAT

, range is 1μF to 22μF. The VIN input

capacitors, C

VIN

is typically between 0.1μF and 2.2μF,

however a larger value will not degrade performance.

Capacitance must be evaluated at the expected bias

voltage, rather than the zero-volt capacitance rating.

PCB Layout Considerations

Layout for linear devices is not as critical as for a switching

regulator. However, careful attention to detail will ensure

reliable operation.

Place input and output capacitors close to

the device for optimal transient response

and device behavior.

Connect all ground connections directly

to the ground plane. If there is no ground

plane, connect to a common local ground

point before connecting to board ground

near the GND pin.

Attaching the part to a larger copper

Applications Information (continued)

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