SC810 datasheet(16/20 Pages) SEMTECH

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SC810

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

), charg-

ing 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 SC810 is 3.6W.

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

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 compli-

ance 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.

Short Circuit Protection

The SC810 can tolerate a BAT pin short circuit to ground

indefinitely. The current into a ground short (while

BAT

< 1.8V) is approximately 10mA. For V

BAT

> 1.8V, normal

pre-charge current regulation is active.

A short circuit or too little programming resistance to

ground on the IPRGM pin (<< 2.05kΩ) will prevent proper

regulation of the BAT pin output current. Prior to enabling

the output a check of the IPRGM pin is performed to

ensure that there is sufficient resistance to ground. A test

current is output on the IPRGM pin. If the test current

produces a voltage of sufficient amplitude, then the

output is enabled. An example with R

IPRGM

= 2.94kΩ is

illustrated in Figure 5, in which the test current is applied

for approximately 250μs to determine that there is no pin

short. If a short is detected, the test current persists until

the short to ground is removed, and then the charging

startup sequence will continue normally.

400μs/div

Figure 5 — IPRGM Pin Short-to-Ground Test During

Startup

A short to ground applied to the IPRGM pin while charg-

ing will also be detected, by a different method. IPRGM

pin short-to-ground detection on the IPRGM pin forces

the SC810 into reset. When the IPRGM ground short is

removed, the charger begins normal operation automati-

cally 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

Applications Information (continued)

BAT

(500mA/div)

BAT

=0mA—

IPRGM

=0V—

VIN

(5V/div)

IPRGM

(1V/div)

VIN

=0V—

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