MAX1686HEUA-T Maxim Integrated Products, MAX1686HEUA-T Datasheet - Page 6

• Manufacturer Part Number: MAX1686HEUA-T
• Description: Charge Pumps 3-5V Regulating Chrg Pump For SIM Cards
• Manufacturer: Maxim Integrated Products

Specifications of MAX1686HEUA-T

• Function: Step Up
• Output Voltage: 5 V
• Output Current: 12 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: uMAX-8
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT

3V to 5V Regulating
Charge Pumps for SIM Cards
1µA. Other features include soft-start, undervoltage
lockout, and short-circuit protection.
Figure 2 shows an idealized, unregulated charge-pump
voltage doubler. The oscillator runs at a 50% duty
cycle. During one half of the period, the transfer capac-
itor (C
half, the doubler stacks the voltage across C
input voltage, and transfers the sum of the two voltages
to the output filter capacitor (C
Skip Mode control to regulate its output voltage and to
achieve good efficiency over a large output current
range. When the comparator detects that the output
voltage is too low, the 1MHz oscillator is enabled and
C
lation, the oscillator is disabled and C
the input.
In the 5V mode (3/5 = GND), the start-up current is lim-
ited by the soft-start control to typically 200mA, inde-
pendent of the load. Until the output voltage reaches
V
50Ω series P-channel MOSFET and the charge pump
is disabled. For V
MAX1686H) and for a maximum of 2ms the charge
pump is active, but R
50Ω. This limits typical current surges associated with
charge pumps at start-up. When soft-start is complete,
V
occurs first), switch S2’s on-resistance is decreased to
minimize losses.
Figure 2. Unregulated Voltage Doubler
6
IN
OUT
C
X
IN
IN
is switched. When the output voltage is above regu-
_______________________________________________________________________________________
/ 2, the input is connected to the output through a
> 4.75V (5.00V for MAX1686H) or 2ms (whichever
X
) charges to the input voltage. During the other
S1
CXN
IN
/ 2 < V
ON
OSC
C
X
of the switch S2 is limited to
Charge-Pump Control
CXP
OUT
OUT
). The MAX1686 uses
S2
< 4.75V (5.00V for
X
is connected at
Soft-Start
X
and the
C
GND
OUT
OUT
In 3V mode (3/5 = IN), the start-up current is limited by
the 50Ω series P-channel MOSFET connected between
IN and OUT until the output voltage reaches V
V
With a 500Ω load the device turns on in less than 1.5ms
(see Typical Operating Characteristics for graphs of
start-up waveforms).
Driving SHDN low places the device in shutdown mode,
which disables the oscillator, the control logic, and the
reference. Placing the device in shutdown mode
reduces the no-load supply current to less than 1µA; the
output is actively discharged through the internal N-
channel FET and disconnected from the input. In normal
operation, SHDN is driven high or connected to IN.
The MAX1686 requires only three external capacitors.
The capacitor values are closely linked to the output
current capability, noise, and switching frequency. The
1MHz oscillator frequency minimizes capacitor size
compared to lower-frequency charge pumps.
Generally, the transfer capacitor (C
smallest, the input capacitor (C
of C
to 50 times C
C
shown in Figure 3. For input voltages as low as 2.7V,
the following values are recommended: C
C
Figure 3. Standard Application Circuit
2.85V TO 4.2V
OUT
X
IN
0.1 F
INPUT
= 0.22µF, and C
C
X
= 0.1µF, C
IN
, and the output capacitor (C
> V
3V
IN
5V
/ 2, R
X
Applications Information
. The suggested capacitor values are
3
2
1
X
ON
IN
SHDN
3/5
= 0.047µF, and C
OUT
is reduced to 2.5Ω.
6
CXN
GND
4
MAX1686
0.047 F
= 10µF. Table 1 lists the perfor-
C
X
PGND
CXP
5
Capacitor Selection
7
IN
OUT
) will be twice the size
OUT
Shutdown Mode
8
OUT
) can be from 10
X
OUTPUT
V
IN
) will be the
IN
OR 4.75V AT 20mA
= 2.2µF as
C
2.2 F
(CERAMIC)
= 0.47µF,
IN
OUT
/ 2. For