MAX8561ETA+T Maxim Integrated Products, MAX8561ETA+T Datasheet - Page 7

• Manufacturer Part Number: MAX8561ETA+T
• Description: IC DC-DC CONV ADJ 500MA 8-TDFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX8561ETA+T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 2.5 V
• Current - Output: 500mA
• Frequency - Switching: 4MHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TDFN Exposed Pad
• Power - Output: 1.95W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Connecting SHDN to GND or logic low places the
MAX8560/MAX8561/MAX8562 in shutdown mode and
reduces supply current to 0.1µA. In shutdown, the con-
trol circuitry, internal-switching P-channel MOSFET, and
synchronous rectifier (N-channel MOSFET) turn off and
LX becomes high impedance. Connect SHDN to IN or
logic high for normal operation.
The MAX8560/MAX8561/MAX8562 have internal soft-
start circuitry that eliminates inrush current at startup,
reducing transients on the input source. Soft-start is par-
ticularly useful for higher impedance input sources,
such as Li+ and alkaline cells. See the Soft-Start and
Shutdown Response graphs in the Typical Operating
Characteristics section.
The 8-pin TDFN versions, the MAX8561 and MAX8562,
include an extra, internal, open-drain N-channel MOSFET
switch that can save an additional package in space-con-
strained applications. The open drain is connected to
ODO, while the gate is controlled by a digital input at
ODI. For the MAX8561, this circuit can be used to toggle
between two regulated output voltages, as in Figure 2.
For the MAX8562, a 10kΩ resistor pulls ODO up to IN
when ODI is low, and the buck converter is forced into
100% duty cycle when ODI is high. This makes the
MAX8562 ideal for driving an external bypass PFET for
high-power mode in CDMA cell phones, as in Figure 3.
The MAX8560/MAX8561/MAX8562 are optimized for
use with tiny inductors and small ceramic capacitors.
The correct selection of external components, especial-
ly C
fast transient response.
Select an output voltage between 0.6V and 2.5V by
connecting FB to a resistive voltage-divider between LX
and GND (see the Typical Operating Circuit). Choose
R2 for a reasonable bias current in the resistive divider.
A wide range of resistor values is acceptable, but a
good starting point is to choose R2 as 100kΩ. Then, R1
is given by:
where V
FF
, ensures high efficiency, low output ripple, and
FB
= 0.6V.
Applications Information
DC-DC Converters in Thin SOT and TDFN
R
_______________________________________________________________________________________
1
=
Setting the Output Voltage
R
4MHz, 500mA Synchronous Step-Down
2



V
V
OUT
FB
Open-Drain Output
−
1
Shutdown Mode



Soft-Start
The MAX8560/MAX8561/MAX8562 operate with inductors
of 1µH to 4.7µH. Low inductance values are smaller but
require faster switching, which results in some efficiency
loss. See the Typical Operating Characteristics section
for efficiency and switching frequency vs. inductor value.
The inductor’s DC current rating only needs to match the
maximum load current of the application + 50mA
because the MAX8560/MAX8561/ MAX8562 feature zero
current overshoot during startup and load transients.
For output voltages above 2.0V, when light-load efficien-
cy is important, the minimum recommended inductor is
2.2µH. For optimum voltage-positioning load transients,
choose an inductor with DC series resistance in the
50mΩ to 150mΩ range. For higher efficiency at heavy
loads (above 200mA) or minimal load regulation (but
some transient overshoot), the resistance should be kept
below 100mΩ. For light-load applications up to 200mA,
much higher resistance is acceptable with very little
impact on performance.
Figure 1. Simplified Functional Diagram
SHDN
ODI
MAX8561*
MAX8562*
MAX8560
*NOTE: ODI/ODO AVAILABLE IN THE MAX8561/MAX8562 ONLY.
THE MAX8561 ODO IS AN OPEN-DRAIN OUTPUT. THE MAX8562
HAS AN INTERNAL 10kΩ PULLUP TO IN.
**GND FOR MAX8560.
LOGIC
PWM
Inductor Selection
NFET
PFET
0.6V
10kΩ
GND
IN
PGND
(GND)**
FB
ODO
LX
7