Datasheet

17
Maxim Integrated
Dual-Input Linear Charger, Smart Power Selector
with Advanced Battery Temperature Monitoring
MAX8934G
Detailed Description
The MAX8934G is a dual-input linear charger with Smart
Power Selector that safely charges a single Li+/Li-Poly cell
in accordance with JEITA specifications. The MAX8934G
integrates power MOSFETs and control circuitry to manage
power flow in portable devices. See Figure 1. The charger
has two power inputs, DC and USB. These can be sepa-
rately connected to an AC adapter output and a USB port,
or the DC input could be a single power input that connects
to either an adapter or USB. Logic inputs, PEN1 and PEN2,
select the correct current limits for two-input or single-input
operation. Figure 2 is the typical application circuit using
separate DC and USB connectors. Figure 3 is the typical
application circuit using a 5-pin USB connector or another
DC/USB common connector.
In addition to charging the battery, the MAX8934G also
supplies power to the system through the SYS output. The
charging current is also provided from SYS so that the set
input current limit controls the total SYS current, where total
SYS current is the sum of the system load current and the
battery-charging current. SYS is powered from either the
DC input pin or the USB input pin. If both the DC and USB
sources are connected, DC takes precedence.
In some instances, there may not be enough adapter
current or USB current to supply peak system loads. The
MAX8934G Smart Power Selector circuitry offers flexible
power distribution from an AC adapter or USB source to
the battery and system load. The battery is charged with
any available power not used by the system load. If a
system load peak exceeds the input current limit, supple-
mental current is taken from the battery. Thermal limiting
prevents overheating by reducing power drawn from the
input source.
The MAX8934G features an overvoltage limiter at SYS. If
the DC or USB input voltage exceeds the SYS regulation
voltage, V
SYS
does not follow V
DC
or V
USB
, but remains
at its regulation voltage. The MAX8934G has numerous
other charging and power-management features that are
detailed in the following sections.
A 3.3V ultra-low quiescent current, always-on LDO pro-
vides up to 30mA for indicator LEDs and for backup
power to the system. This LDO powers the thermistor
monitor circuitry and provides bias to the external pullup
resistor for the thermistor.
Table 1. External Components List for Figures 2 and 3
COMPONENT
(Figures 2 and 3)
FUNCTION PART NUMBER
C
DC
DC filter capacitor
10FF ±10%, 16V X5R ceramic capacitor (0805)
Taiyo Yuden EMK212BJ106KG
C
USB
USB filter capacitor
4.7FF ±10%, 10V X5R ceramic capacitor (0805)
Taiyo Yuden LMK212BJ475KD
C
VL
V
L
filter capacitor
0.1FF ±10%, 10V X5R ceramic capacitor (0402)
Taiyo Yuden LMK105BJ104KV
C
SYS
SYS output bypass capacitors
10FF ±10%, 6.3V X5R ceramic capacitor (0805)
Taiyo Yuden JMK212BJ106KD
C
BATT
Battery bypass capacitor
4.7FF ±10%, 6.3V X5R ceramic capacitor (0805)
Taiyo Yuden JMK212BJ475KD
C
CT
Charger timing capacitor
0.068FF ±10%, 16V X5R ceramic capacitor (0402)
Taiyo Yuden EMK105BJ683KV
C
LDO
LDO output capacitor
1FF ±10%, 6.3V X5R ceramic capacitor (0402)
Taiyo Yuden JMK105BJ105KV
R
PU
(x5) Logic-output pullup resistors
1MI ±5% resistor
THM Negative TC thermistor Vishay NTC Thermistor P/N NTHS0603N01N1003FF
R
THMSW
THM pullup resistor
100kI
R
PSET
DC input current-limit programming resistor
1.5kI ±1% for 2A limit
R
ISET
Fast-charge current programming resistor
3kI ±1% for 1A charging