ADP3801/ADP3802

–12–

REV. 0

SD results in shutdown. All internal circuitry is shut off except

for the LDO and the reference, and the supply current is typi-

cally 110

µA. When SD returns high, the part resumes full op-

eration. The compensation capacitor at the COMP node is

discharged during shutdown, so the part will resume operation

in soft-start mode.

Undervoltage Lockout—UVLO

The internal Undervoltage Lockout (UVLO) circuit monitors

the input voltage and keeps the part in shut-down mode until

VCC rises above 3.9 V. During UVLO, the LDO and reference

are still active, but the analog front end, the oscillator, and the

gate drive are off. UVLO helps to prevent the circuitry from

entering an unknown state that could incorrectly charge a battery.

To prevent oscillation around VCC = 3.9 V, the UVLO cir-

cuitry has built-in hysteresis. Once the part is on, the UVLO

circuitry does not shut it off until the LDO enters dropout.

Because the dropout voltage depends on the LDO’s load, the

UVLO trip point-off also depends on the load. Refer to Figure 8

for a graph of the UVLO trip point-off versus LDO load.

RESET

When the power is first applied to the ADP3801/ADP3802, the

RESET pin is held at ground by an external 1 M

Ω resistor. It

remains low until the LDO output voltage rises to above 80% of

its final value. When this threshold is reached, the RESET pin is

pulled high. The internal RESET comparator includes about

150 mV of hysteresis to avoid oscillation around the threshold.

Supply Considerations

The guaranteed operating supply voltage range of the ADP3801/

ADP3802 is from 4 V to 20 V, and it typically consumes 5.0 mA

of quiescent current when not switching. However, the part

needs at least 2 V of headroom between VCC and the voltage

on the CS+ and CS– pins. This is for the common-mode range

on the current sense amplifier. In applications where the input

supply does not offer enough headroom, the circuits in Figures

32 and 33 can be used as explained in the section on low over-

head charging.

Overtemperature Shutdown

The ADP3801/ADP3802 has an on-chip temperature detector

to shut the part down when the die temperature reaches typi-

cally +160

°C. Such a condition could occur with a short-circuit

on the LDO or a short on the DRV pin. In either case, the op-

eration of the charger will stop and the DRV pin will be pulled

high. With approximately +10

°C hysteresis, the overtemperature

shutdown releases at typically +150

°C. These temperatures are

higher than the absolute maximum ratings for the die, and are

included as a safety feature only.

Li-Ion Battery Charger

The ADP3801 and ADP3802 are ideally suited for a single or

dual Li-Ion batterypack charger. They combine 200 kHz or

500 kHz switching with a PMOS pass transistor drive to realize

a Buck topology CCCV charger. The following discussion goes

through the complete design of a charger using the ADP3801.

This information also applies to the ADP3802.

Charger Specifications

Battery: 3 Series Cell Li-Ion Pack.

Circuit Topology

The complete Buck charger circuit is shown in Figure 24. The

dc-source voltage can be supplied from an ac/dc adaptor or an

external dc/dc supply.

MBRD835

40m

BATA

TOP VIEW

(Not to Scale)

DRV

VL

SD

CS–

CS+

GND

A/B

BATA

BATB

PROG

ADJ

EOC

COMP

ADP3801/

ADP3802

VCC

RESET

0.1 F

210 F

25V

1k

140 F

25V

4.3k

4.3k

C7

2.2nF

C9

2.2nF

MBRD835

ISET

100k

SD

VL = +3.3V

4.7 F

100k

24k

20k

1.0 F

EOC

1M

RESET

(+15V TO +20V)

33 H

Si4463

56

100k

200k

Figure 24. Li-Ion Battery Charger