MAX8731EVSYS Maxim Integrated, MAX8731EVSYS Datasheet - Page 22

• Manufacturer Part Number: MAX8731EVSYS
• Description: Battery Management SMBus Level 2 Battery Charger with Remote Sense
• Manufacturer: Maxim Integrated
• Series: MAX8731Ar

Specifications of MAX8731EVSYS

• Battery Type: Li-Ion, Li-Polymer, NiCd, NiMH, Lead Acid, Universal
• Output Voltage: 5.4 V
• Operating Supply Voltage: 8 V to 26 V
• Charge Safety Timers: Yes
• Operating Supply Current: 2 uA
• Product Type: Charge Management
• Temperature Monitoring: No
• Uvlo Start Threshold: 2.5 V
• Uvlo Stop Threshold: 100 mV

The MAX8731 supports four battery-charger com-
mands that use either Write-Word or Read-Word proto-
cols, as summarized in Table 4. ManufacturerID() and
DeviceID() can be used to identify the MAX8731. On
the MAX8731, the ManufacturerID() command always
returns 0x004D and the DeviceID() command always
returns 0x0008.
The MAX8731 employs a synchronous step-down DC-
DC converter with an n-channel high-side MOSFET
switch and an n-channel low-side synchronous rectifier.
The MAX8731 features a pseudo-fixed-frequency, cur-
rent-mode control scheme with cycle-by-cycle current
limit. The controller’s constant off-time (t
ed based on V
minimum value of 300ns. The MAX8731 can also oper-
ate in discontinuous-conduction mode for improved
light-load efficiency. The operation of the DC-DC con-
troller is determined by the following four comparators
as shown in the functional diagrams in Figures 2 and 6:
SMBus Level 2 Battery Charger with
Remote Sense
Table 4. Battery-Charger Command Summary
Figure 6. DC-DC Converter Functional Diagram
22
ChargeVoltage ( )
COMMAND
______________________________________________________________________________________
CSI
0x14
0x15
0x3F
0xFE
0xFF
+100mV
DCIN
CSIN
FBS_
150mV
LVC
100mV
2V
CSSP
CCMP
ZCMP
COMPUTE
ChargeCurrent()
ChargeVoltage()
InputCurrent()
ManufacturerID()
DeviceID()
IMAX
OFF-TIME
IMIN
OVP
COMMAND NAME
Battery-Charger Commands
, V
CSIN
, and a time constant with a
DC-DC Converter
ONE-SHOT
OFF-TIME
R
S
Q
Q
DH
DRIVER
OFF
READ/WRITE
) is calculat-
Read Only
Read Only
Write Only
Write Only
Write Only
DL
DRIVER
6-Bit Charge-Current Setting
11-Bit Charge-Voltage Setting
6-Bit Charge-Current Setting
Manufacturer ID
Device ID
The IMIN comparator triggers a pulse in discontinuous
mode when the accumulated error is too high. IMIN
compares the control signal (LVC) against 100mV (typ).
When LVC is less than 100mV, DHI and DLO are both
forced low. Indirectly, IMIN sets the peak inductor cur-
rent in discontinuous mode.
The CCMP comparator is used for current-mode regu-
lation in continuous-conduction mode. CCMP com-
pares LVC against the inductor current. The high-side
MOSFET on-time is terminated when the CSI voltage is
higher than LVC.
The IMAX comparator provides a secondary cycle-by-
cycle current limit. IMAX compares CSI to 2V (corre-
sponding to 10A when RS2 = 10mΩ). The high-side
MOSFET on-time is terminated when the current-sense
signal exceeds 10A. A new cycle cannot start until the
IMAX comparator’s output goes low.
The ZCMP comparator provides zero-crossing detec-
tion during discontinuous conduction. ZCMP compares
the current-sense feedback signal to 750mA (RS2 =
10mΩ). When the inductor current is lower than the
750mA threshold, the comparator output is high and
DLO is turned off.
The OVP comparator is used to prevent overvoltage at
the output due to battery removal. OVP compares FBS_
against the set voltage (ChargeVoltage()). When FBS_
is 100mV above the set value, the OVP comparator out-
put goes high and the high-side MOSFET on-time is ter-
minated. DHI and DLO remain off until the OVP
condition is removed.
The MAX8731 controls input current (CCS control loop),
charge current (CCI control loop), or charge voltage
(CCV control loop), depending on the operating condi-
tion. The three control loops—CCV, CCI, and CCS—are
brought together internally at the lowest voltage-clamp
(LVC) amplifier. The output of the LVC amplifier is the
feedback control signal for the DC-DC controller. The
minimum voltage at the CCV, CCI, or CCS appears at
the output of the LVC amplifier and clamps the other
control loops to within 0.3V above the control point.
CCV, CCI, CCS, and LVC Control Blocks
DESCRIPTION
POR STATE
0x004D
0x0000
0x0000
0x0080
0x0008