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2770EAR

Battery Monitor and Charge Controller

Dallas Semiconductor -> Maxim Integrated 

DS2770

POWER MODES

The DS2770 has two possible power modes: Active Mode and Sleep Mode. While in Active Mode, the

DS2770 continually measures current, voltage, temperature, and time. Also, current flow is accumulated,

charge control is provided, and data is available to the host system. In Sleep Mode, the DS2770 ceases

these activities. The DS2770 can enter Sleep Mode only when the PMOD bit in the Status Register is set

to 1 and the following other conditions occur:

§ The CINI bit is set to 0 and the DQ line is held low for longer than two seconds. If a charge is in

progress, charging will immediately stop and the device will begin transition to Sleep Mode.

§ The CINI bit is set to 1 and the DQ line is held low for longer than two seconds. If a charge is in

progress, the DS2770 will not go into Sleep Mode until the charge operation is completed.

The DS2770 returns to Active Mode when any of the following occurs:

§ The DQ line is pulled high.

§ The voltage on VCH becomes greater than VDD (charger connection) with the CINI bit set to 1.

Once the DS2770 identifies the 2 second DQ low condition, a transition to Sleep Mode begins. This

process will take up to an additional 11 seconds before the supply current drops to ISLEEP levels.

The DS2770 defaults to Active Mode when power is first applied to VDD.

CHARGER FUNCTION

The DS2770 operates as a standalone charge controller supporting rechargeable lithium and NiMH

battery technologies. The battery type to be charged is selectable through the CTYPE bit of the Status

Register (0 for rechargeable lithium and 1 for NiMH). Charge control of both battery types is performed

by on/off gating of an external constant current or current-limited charge source. If the battery voltage is

less than VLB and a charge source is present, pin UV is driven low, signifying the need to recover the

battery at a reduced rate before fast charging can begin. In Figure 2’s application circuit, UV gates a

trickle-charge current limited by a 360W series resistor. Selection of this resistor depends on the

characteristics of the charge source. UV is driven low independent of any other state of the pack,

including pack temperature and the status of the CINI bit. UV is driven high when the battery voltage

reaches VLB. While trickle charging, a “charge in progress” status is indicated with (0, 1) values,

respectively, in the CSTAT1 and CSTAT0 bits of the Status Register assuming any previous charge

sequence completed status has been cleared.

Fast charging can be initiated by one of two methods:

1) Issuing a Start Charge command [B5h].

2) Introducing a charge supply on the VCH pin when the CINI bit in the Status Register is a 1.

Note that if VDD is below approximately 1.8V prior to using either initiation method, fast charge will not

start after the battery is trickle charged to VLB.

After initiation, the start of fast charge may be postponed if any of the following conditions exist:

§ The temperature is outside the valid charge window specified by TCL (0°C) and TCH (40°C).

§ Charge source is not present (VCH < VDD).

§ Conversion data is not valid (data becomes valid 110ms after waking from Sleep Mode).

§ Battery voltage is less than the low-battery-voltage threshold, VLB, (3.0V).

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