SC824 datasheet(22/29 Pages) SEMTECH

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SC824

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 5 — Thermal Limiting Example

Note that the BAT output current is rapidly reduced to

limit the internal die temperature. It then continues to

decline as the circuit board temperature gradually rises,

further reducing the conduction of heat from the die to

the ambient environment. 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 Char ger and Inter f a c e for Mobile

Telecommunication Terminal, Section 4.2.3.1.

Short Circuit Protection

The SC824 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 (<< 2kΩ) 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 6, 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.

400μs/div

Figure 6 — 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 mechanism. IPRGM

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

the SC824 into reset, turning off the output and clearing

the logical state, including the timer.

A short-to-ground on the IPRGM pin will halt charging

and prevent startup regardless of the mode selected. It is

indicated as a fault condition on the STATx pins. When the

IPRGM ground short 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 the programmed pre-charge current limit value when

the battery voltage is below the pre-charge threshold and

the fast-charge current limit value otherwise.

Logical State Machine

The SC824 logical behavior described in the preceding

sections is derived from two distinct state machines, as

illustrated in the following diagrams. The charger state

machine permits transitions to most states from most

other states, as shown. The multi-stage timer state

machine enforces a unidirectional flow. Once the timer

has advanced from one stage to the next, there is no

return to the previous stage except by a re-charge cycle, a

reset (by disabling and re-enabling the SC824), or by

cycling the input power off and on.

Applications Information (continued)

BAT

(500mA/div)

BAT

=0mA—

IPRGM

=0V—

VIN

(5V/div)

IPRGM

(1V/div)

VIN

=0V—

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