Rainbow Electronics DS2784 - Manual (Page 9)

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
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RNAOP —Read Net Address Op Code. A value of 0 selects 33h as the op code value for the Read Net Address
command. A value of 1 selects 39h as the Read Net Address opcode value.
0 —Reserved bit, must be programmed to 0 for proper operation.
PSPIO —Power-Switch PIO Enable. A value of 1 enables the PIO pin as a power-switch input. A value of 0 disables
the power-switch input function on PIO pin. This control is independent of the PSDQ state.
PSDQ —Power-Switch DQ Enable. A value of 1 enables the DQ pin as a power-switch input. A value of 0 disables
the power-switch input function on DQ pin. This control is independent of the PSPIO state.
X —Reserved Bit.
Li+ PROTECTION CIRCUITRY
During Active mode, the DS2784 constantly monitors SNS, V
IN
, and V
PLS
to protect the battery from overvoltage
(overcharge), undervoltage (overdischarge), and excessive charge and discharge currents (overcurrent, short
circuit). Table 1 summarizes the conditions that activate the protection circuit, the response of the DS2784, and the
thresholds that release the DS2784 from a protection state.
Table 1. Li+ Protection Conditions and DS2784 Responses
ACTIVATION
CONDITION
THRESHOLD DELAY RESPONSE
(2)
RELEASE THRESHOLD
Overvoltage V
IN
> V
OV
t
OVD
CC Off
V
IN
< V
CE
or (V
SNS
> 1.2mV
and V
IN
< V
OV
)
Undervoltage V
IN
< V
UV
t
UVD
CC Off, DC Off,
Sleep Mode
V
PLS
> V
IN
(3)
(charger connected)
Overcurrent, Charge V
SNS
< V
COC
t
OCD
CC Off, DC Off
V
PLS
< V
DD
- V
TP
(4)
(charger removed)
Overcurrent, Discharge V
SNS
> V
DOC
t
OCD
DC Off
V
PLS
> V
DD
- V
TP
(5)
(load removed)
Short Circuit V
SNS
> V
SC
t
SCD
DC Off
V
PLS
> V
DD
- V
TP
(5)
(load removed)
Note 1: All voltages are with respect to V
SS
.
Note 2: CC pin driven to V
OLCC
(V
DD
) for CC off response. DC pin driven to V
OLDC
(V
SS
) for DC off response.
Note 3: If V
IN
< V
UV
when charger connection is detected, release is delayed until V
IN
≥ V
UV
. The recovery charge path provides an internal
current limit (I
RC
) to safely charge the battery.
Note 4: With test current I
TST
flowing from PLS to V
SS
(pulldown on PLS) enabled.
Note 5: With test current I
TST
flowing from V
DD
to PLS (pullup on PLS).
Overvoltage.
If the voltage on V
IN
exceeds the overvoltage threshold (V
OV
) for a period longer than overvoltage
delay (t
OVD
), the CC pin is driven low to shut off the external-charge FET, and the OV flag in the protection register
is set. The DC output remains high during overvoltage to allow discharging. When V
IN
falls below the charge enable
threshold, V
CE
, the DS2784 turns the charge FET on by driving CC high. The DS2784 drives CC high before
V
IN
< V
CE
if a discharge condition persists with V
SNS
≥ 1.2mV and V
IN
< V
OV
.
Undervoltage.
If V
IN
drops below the undervoltage threshold (V
UV
) for a period longer than undervoltage delay
(t
UVD
), the DS2784 shuts off the charge and discharge FETs and sets the UV flag in the protection register. If UVEN
is set, the DS2784 also enters Sleep mode. The DS2784 provides a current-limited recovery charge path (I
RC
) from
PLS to V
DD
to gently charge severely depleted cells. The recovery charge path is enabled when
0 ≤ V
DD
< (V
OV
- 100mV). Once V
DD
reaches 2.45V (typ), the DS2784 returns to normal operation and begins
monitoring V
IN
. Once V
IN
> V
UV
, the DS2784 transitions from Sleep to Active mode and the CC and DC outputs are
driven high to turn on the charge and discharge FETs.
Overcurrent, Charge Direction (COC).
Charge current develops a negative voltage on V
SNS
with respect to V
SS
. If
V
SNS
is less than the charge overcurrent threshold (V
COC
) for a period longer than overcurrent delay (t
OCD
), the