Information

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Portable Power Conversion Design Guide
Backlighting Solutions
Charge Pump DC/DC Converters
Charge Pump DC/DC Converters
The MCP1256, MCP1257, MCP1258 and MCP1259 are inductorless, positive regulated charge pump DC/DC converters.
Generating a regulated 3.3V output voltage from a 1.8V to 3.6V input, they are specifically designed for applications
operating from two-cell alkaline, two-cell Ni-Cd, two-cell Ni-MH, or one primary lithium coin cell battery. These devices
automatically switch from 1.5× to 2× boost operation modes to maintain high efficiency. In addition, at light output loads
the MCP1256 and MCP1257 can be placed in a sleep mode, lowering the quiescent current while maintaining the
regulated output voltage. Alternatively, the MCP1258 and MCP1259 provide a bypass feature connecting the input voltage
to the output. This allows for real-time clocks, microcontrollers or other system devices to remain biased with virtually no
current being consumed by the MCP1258 or MPC1259. In normal operation, the charge pumps switch at a fixed 650 kHz,
avoiding sensitive IF bands, and the output voltage ripple is below 20 mV
P-P
at load currents up to 100 mA. The MCP1256
and MCP1258 feature a power-good output that can be used to detect out-of-regulation conditions. The MCP1257 and
MCP1259 feature a low battery indication that issues a warning if the input voltage drops below a preset voltage
threshold. Extremely low supply current and few external parts (4 capacitors) make these devices ideal for small, battery
powered applications. A Shutdown mode is also provided for further power reduction. The devices incorporate thermal and
short-circuit protection.
■ High accuracy 3.3V ± 3.0% output voltage
■ Accepts 1.8V to 3.6V input voltages
■ Supplies up to 100 mA output current
■ Low 20 mV
P-P
output voltage ripple
■ Integrated thermal shutdown and short circuit
protection
■ Uses small ceramic capacitors
■ Operates at 650 kHz switching frequency
■ Low-power sleep mode feature on MCP1256/7
■ Bypass mode on MCP1258/9
■ Low-power 0.1 μA shutdown mode
■ Shutdown input compatible with 1.8V logic
■ Soft-start circuitry to minimize inrush current
■ Available in 10-pin 3 × 3 DFN or 10-pin MSOP packages
MCP1259 Charge Pump Backlighting Circuit
GND
V
IN
C1+
C1–
C2+
C2–
BOOST
VOUT
VIN
1.6V to 3.6V
V
OUT
3.3V
CIN
10 μF
COUT
10 μF
SHDN
LBO
BYPASS
C
1
1 μF
OFF
ON
C
2
1 μF
R
1
Low Battery
Indicator
MCP1259 Power Conversion Effi ciency