Rainbow Electronics MAX8903A - Manual (Page 9)

MAX8903A
2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power
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Pin Description
PIN NAME FUNCTION
1, 2 PG
Power Ground for Step-Down Low-Side Synchronous n-Channel MOSFET. Both PG pins must be
connected together externally.
3, 4 DC
DC Power Input. DC is capable of delivering up to 2A to SYS. DC supports both AC adapter and USB
inputs. The DC current limit is set through DCM, IUSB, or IDC depending on the input source used. See
Table 2. Both DC pins must be connected together externally. Connect at least a 4.7µF ceramic capacitor
from DC to PG.
5 DCM
Current-Limit Mode Setting for the DC Power Input. When logic-high, the DC input current limit is set by
the resistor at IDC. When logic-low, the DC input current limit is internally programmed to 500mA or
100mA, as set by the IUSB pin.
6 BST High-Side MOSFET Driver Supply. Bypass BST to LX with a 0.1µF ceramic capacitor.
7 IUSB
USB Current-Limit Set Input. Drive IUSB logic-low to set the USB current limit to 100mA. Drive IUSB logic-
high to set the USB current limit to 500mA.
8
DOK
DC Power-OK Output. Active-low open-drain output pulls low when a valid input is detected at DC. DOK
is still valid when the charger is disabled (CEN high).
9 VL
Logic LDO Output. VL is the output of an LDO that powers the MAX8903A internal circuitry and charges
the BST capacitor. Connect a 1µF ceramic capacitor from VL to GND.
10 CT
Charge Timer Set Input. A capacitor (C CT ) from CT to GND sets the fast-charge and prequal fault timers.
Connect to GND to disable the timer.
11 IDC
DC Current-Limit Set Input. Connect a resistor (R IDC ) from IDC to GND to program the current limit of the
step-down regulator from 0.5A to 2A when DCM is logic-high.
12 GND Ground. GND is the low-noise ground connection for the internal circuitry.
13 ISET
Charge Current Set Input. A resistor (R ISET ) from ISET to GND programs the fast-charge current up to 2A.
The prequal charge current is 10% of the fast-charge current.
14
CEN
Charger Enable Input. Connect CEN to GND to enable battery charging when a valid source is connected
at DC or USB. Connect to VL, or drive high to disable battery charging.
15 USUS
USB Suspend Input. Drive USUS logic-high to enter USB suspend mode, lowering USB current to 115µA,
and internally shorting SYS to BAT.
16 THM
Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor from THM to GND.
Connect a resistor equal to the thermistor +25°C resistance from THM to VL. Charging is suspended
when the thermistor is outside the hot and cold limits. Connect THM to GND to disable the thermistor
temperature sensor.
17 USB
USB Power Input. USB is capable of delivering 100mA or 500mA to SYS as set by the IUSB logic input.
Connect a 4.7µF ceramic capacitor from USB to GND.
18
FLT
Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or
fast-charge completes.
19
UOK
USB Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at USB.
UOK is still valid when the charger is disabled (CEN high).
20, 21 BAT
Battery Connection. Connect to a single-cell Li+ battery. The battery charges from SYS when a valid
source is present at DC or USB. BAT powers SYS when neither DC nor USB power is present, or when the
SYS load exceeds the input current limit. Both BAT pins must be connected together externally.