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© 2005 Semtech Corp.

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SC804A

PRELIMINARY

POWER MANAGEMENT

DRAFT

The actual dropout voltage is the greater of the Minimum Dropout

Voltage at various programmed V

voltages (shown here, with several programmed V

indicated in the figure by ‘o’), and the IR drop due to the product

of IOUT and R

Adjust mode operation is

ensured for any IOUT current at programmed V

approximately 4.41V.

Applications Information (Cont.)

FLAG

ON

OFF

CPB

UVLO < VCC < OVP

Input out of range

CHRGB

IOUT > ITERM

IOUT < ITERM

OVPB

VCC > OVP

VCC < OVP

FLTB

VCC > OVP

VCC UVLO

NTC Temp Fault

Pre-Charge Time-out

(OT (Tj > 150°C)

Normal Operation or

NTC Disable

NOTE: When using Adjust Mode to program a CV regulation

voltage greater than V

charging with a charging adapter operating in current

limit.

Adapter current-limited operation occurs when

the adapter current limit is less than the programmed

SC804A fast charge current, such that the adapter voltage

is pulled down to V

A low adapter current limit multiplied by the low minimum

path resistance of the main pass transistor and current

sense resistor (as low as 290m

Ω total at extremely low

temperature) can result in a voltage drop from VCC to

VOUT of less than 150mV if the Adjust Mode CV regulation

voltage is programmed above V

< 150mV, Adjust Mode may not operate correctly. Adjust

Mode will operate correctly whenever the programmed

VOUT CV voltage is less than V

adapter current limit, because the regulated minimum

dropout voltage is always greater than 150mV in this

case. It will also operate correctly with an adapter current

limit greater than 550 mA, regardless of the programmed

output voltage, because the I-R dropout voltage will

exceed 150mV at even the lowest specified operating

temperature. Normal mode (that is, not Adjust Mode) has

a regulated minimum dropout voltage of approximately

200mV, which is constant for any V

correctly for any adapter current limit.

Overcurrent and Max Temperature Protection

Overcurrent protection is inherent in all modes of operation.

When the device is in charge mode the output is current-

limited to either the pre-charge current limit value or the

fast charge current limit value depending on the voltage

at the output. Max die temperature protection is also

included. This feature allows the SC804A to operate

with maximum power dissipation by disabling the output

current when the die temperature reaches the maximum

operating temperature. The result is that the SC804A will

operate as a pulse charger in extreme power dissipation

applications, delivering the maximum allowable output

current while regulating the internal die temperature to a

safe level.

Indicator Flags

There are four indicator outputs/LED drivers ont he

SC804A; CPB (Charger Present), CHRGB (Charge Active),

OVPB (Over Voltage Fault), and FLTB (Fault). These outputs

are all active-low; open drain NMOS drivers capable of

sinking up to 10mA. The following table defines each

indicator’s output state.

The CPB output can be used as a VCC-present indicator.

Regardless of teh state of NTC, the CPB output reflects

the VCC voltage. When V

thresholds the CPB output is low. If V

limits, this output is high impedance.

The CHRGB output indicates the charging status. When

the output current is greater than ITERM, CHRGB is low.

CHRGB is high impedance when IOUT is less than ITERM.

The CHRGB output is latched during the charge cycle

when the output current is less than ITERM. This latch is

reset when the battery enters a recharge cycle, or if NTC

or VCC are toggled.

3.2

3.4

3.6

3.8

4

4.2

4.4

4.6

0.2

0.4

0.6

0.8

Output voltage, V

Figure 4 - Adjust Mode Minimum Dropout Voltage