MAX1759EUB-T Maxim Integrated Products, MAX1759EUB-T Datasheet - Page 6

• Manufacturer Part Number: MAX1759EUB-T
• Description: Charge Pumps Buck/Boost Regulating
• Manufacturer: Maxim Integrated Products

Specifications of MAX1759EUB-T

• Function: Step Up, Step Down
• Output Voltage: 3.3 V, 2.5 V to 5.5 V
• Output Current: 100 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: uMAX-10
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT

Buck/Boost Regulating
Charge Pump in µMAX
The MAX1759’s unique charge-pump architecture
allows the input voltage to be higher or lower than the
regulated output voltage. Internal circuitry senses V
and V
stepped up or stepped down to produce the regulated
output. When V
operates as a regulated step-up voltage doubler. When
V
a step-down gated switch.
In voltage step-down mode (i.e., the input voltage is
greater than the output voltage) with a light load, the
controller connects CXN to PGND, and shuttles charge
to the output by alternately connecting CXP from IN to
OUT (see Figures 1 and 2). Although V
V
late the output under heavy loads. In this case, the
MAX1759 will automatically switch to step-up mode. In
step-up mode, the output is kept in regulation by modu-
lating the charge delivered by the transfer capacitor
(C
charge pump switches only as necessary to supply the
load, resulting in low quiescent current. Output voltage
ripple does not increase with light loads.
Driving SHDN low places the MAX1759 in shutdown
mode. This disables the charge-pump switches, oscil-
lator, and control logic, reducing quiescent current to
1µA. The output is high impedance in shutdown and is
disconnected from the input. The POK output is high
impedance in shutdown.
The MAX1759 undervoltage lockout feature deactivates
the device when the input voltage falls below 1V.
POK is an open-drain output that sinks current when
the regulator feedback voltage falls below 1.1V. The
feedback voltage can be either the internal resistor-
divider feedback voltage when in fixed output mode
(FB tied to GND) or an external feedback voltage from
an external resistive divider in adjustable output mode.
A 10kΩ to 1MΩ pull-up resistor from POK to OUT may
be used to provide a logic output. Connect POK to GND
or leave unconnected if not used.
The MAX1759 features foldback short-circuit protec-
tion. This circuitry provides soft-start by limiting inrush
current during startup and limits the output current to
110mA (typ) if the output is short-circuited to ground.
6
IN
OUT
X
) to the load (see Figure 2). When lightly loaded, the
_______________________________________________________________________________________
is higher than V
, this scheme may not allow the MAX1759 to regu-
Soft-Start and Short-Circuit Protection
OUT
and determines whether V
IN
is lower than V
OUT
Detailed Description
, the charge pump operates as
Undervoltage Lockout
OUT
Power-OK Output
Shutdown Mode
, the charge pump
IN
is greater than
IN
must be
IN
The MAX1759 features thermal shutdown with tempera-
ture hysteresis. When the die temperature exceeds
160°C, the device shuts down. When the die cools by
20°C, the MAX1759 turns on again. If high die tempera-
ture is caused by output overload and the load is not
removed, the device will turn off and on, resulting in a
pulsed output.
The MAX1759 dual-mode feedback controller selects
between the internally set 3.3V regulated output or an
external resistive divider that allows adjustment of the
output voltage from 2.5V to 5.5V. Connect FB to GND
for a regulated 3.3V output. For an adjustable output,
connect a resistive divider between OUT and GND. To
ensure feedback-loop stability and to minimize error due
to FB pin bias currents, the resistive divider current
should be approximately 15µA. In the following equa-
tion, choose R2 in the 50kΩ to 100kΩ range, and calcu-
late R1 from the following formula (Figure 3):
and
where V
5.5V, and V
nally 1.235V.
The circuit of Figure 3 generates a regulated 2.5V, using
external standard 1% resistor values. Surface-mount
resistors should be placed close to the MAX1759, less
than 5mm away from FB (see the PC Board Layout
section).
Figure 1. Typical Application Circuit
ON
10µF
+1.6V TO +5.5V
OUT
OFF
IN
FB
is the desired output voltage from 2.5V to
R1 = R2 [(V
V
OUT
is the internal regulation voltage, nomi-
IN
SHDN
= V
Setting the Output Voltage
CXN
FB
FB
MAX1759
0.33µF
OUT
GND
(R1 + R2) / R2
Design Procedure
PGND
/ V
CXP
Thermal Shutdown
FB
OUT
POK
) - 1]
100k
3.3V AT 100mA
POWER OK
OUT
10µF