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SC804

PRELIMINARY

POWER MANAGEMENT

current and the charge path resistance from VOUT to the

Kelvin sense point should not exceed 150mV to ensure

normal mode operation.

The SC804 Adjust Mode schematic is shown in Figures 3A

and 3B. Referring to these schematics, the equation for

setting the output voltage is:

The capacitor C3 across R8 in the feedback network

introduces zero-pole frequency compensation for stability.

Place the zero according to the following equation to

ensure stability:

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

SC804 fast charge current, such that the adapter voltage

is pulled down to V

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.

Over current and Max Temperature Protection

Over current protection is inherent in all modes of

R11 × C3 =

1

2 × 100kHz

Applications Information (Cont.)

VOUT = V

R12

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 SC804 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 SC804 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 on the SC804:

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 the 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.

3.2

3.4

3.6

3.8

4

4.2

4.4

0.2

0.4

0.6

0.8

Output voltage, V

Figure 4 - Adjust Mode Minimum Dropout Voltage

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 4.25V.