Rainbow Electronics MAX619 - Manual (Page 4)

MAX619
Regulated 5V Charge-Pump
DC-DC Converter
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_______________Detailed Description
Operating Principle
The MAX619 provides a regulated 5V output from a 2V
to 3.6V (two battery cells) input. Internal charge pumps
and external capacitors generate the 5V output, elimi-
nating the need for inductors. The output voltage is
regulated to 5V ±4% by a pulse-skipping controller that
turns on the charge pump when the output voltage
begins to droop.
To maintain the greatest efficiency over the entire input
voltage range, the MAX619’s internal charge pump
operates as a voltage doubler when V
IN ranges from
3.0V to 3.6V, and as a voltage tripler when V IN ranges
from 2.0V to 2.5V. When V IN ranges from 2.5V to 3.0V,
_____________________Pin Description the MAX619 switches between doubler and tripler
mode on alternating cycles, making a 2.5 x V
IN charge
pump. To further enhance efficiency over the input
range, an internal comparator selects the higher of V
IN
or V OUT to run the MAX619’s internal circuitry.
Efficiency with V IN = 2V and I OUT = 20mA is typically
80%.
Figure 1 shows a detailed block diagram of the
MAX619. In tripler mode, when the S1 switches close,
the S2 switches open and capacitors C1 and C2
charge up to V
IN . On the second half of the cycle, C1
and C2 are connected in series between IN and OUT
when the S1 switches open and the S2 switches close,
as shown in Figure 1. In doubler mode, only C2 is
used.
During one oscillator cycle, energy is transferred from
the input to the charge-pump capacitors, and then
from the charge-pump capacitors to the output capaci-
tor and load. The number of cycles within a given time
frame increases as the load increases or as the input
supply voltage decreases. In the limiting case, the
charge pumps operate continuously, and the oscillator
frequency is nominally 500kHz.
Shutdown Mode
The MAX619 enters low-power shutdown mode when
SHDN is a logic high. SHDN is a CMOS-compatible
input. In shutdown mode, the charge-pump switching
action is halted, OUT is disconnected from IN, and
V
OUT falls to 0V. Connect SHDN to ground for normal
operation. When V IN = 3.6V, V OUT typically reaches
5V in 0.5ms under no-load conditions after SHDN goes
low.
FUNCTION NAME PIN
Negative Terminal for C1 C1- 8
Active-High CMOS Logic-Level Shutdown Input SHDN 7
Ground GND 6
Negative Terminal for C2 C2- 5
Positive Terminal for C2 C2+ 4
+5V Output Voltage. V OUT = 0V when in
shutdown mode.
OUT 3
Input Supply Voltage IN 2
Positive Terminal for C1 C1+ 1