MAX1765EUE+T Maxim Integrated Products, MAX1765EUE+T Datasheet - Page 13

• Manufacturer Part Number: MAX1765EUE+T
• Description: IC DC-DC CONV 800MA LN 16TSSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1765EUE+T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 2.5 ~ 5.5 V
• Current - Output: 800mA
• Frequency - Switching: 1MHz
• Voltage - Input: Adj down to 0.7V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Power - Output: 1.5W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

tures a 250mΩ, P-channel MOSFET pass transistor.
This provides several advantages, including longer bat-
tery life, over similar designs using a PNP pass transis-
tor. The P-channel MOSFET requires no base-drive
current. This reduces quiescent current considerably,
since PNP-based regulators tend to waste base-drive
current in dropout when the pass transistor saturates.
Connect the input of the linear regulator (INL) to POUT.
The linear regulator can be used to postfilter the switch-
ing regulator or regulate a separate supply voltage.
This regulated output is intended to power noise-sensi-
tive analog circuitry, such as low-noise amplifiers and
IF stages in cellular phones and other instruments, and
can deliver up to 500mA. Use a 4.7µF capacitor with
less than a 1Ω equivalent series resistance (ESR) on
the output to provide stability. The linear regulator has
an internal 1.3A (max) current limit and thermal-over-
load protection circuitry to protect this output.
There are several useful circuit configurations that can
be implemented with the MAX1765. The TRACK input
divides the circuit configurations into two types, one
where the DC-DC converter tracks to the LDO output,
and the other where the boost and the LDO regulate
independently.
Asserting the TRACK input places the MAX1765 into
track mode, where the DC-DC switching regulator’s
feedback pin (FB) is ignored, and the boost output
(POUT) “tracks” to 500mV above the linear regulator
output. The primary use of the MAX1765 in TRACK
mode is as a simple or very-low-noise step-up/down
power supply (see Figures 3 and 4; also see the
Maximum Output Current vs. Input Voltage plot in the
Typical Operating Characteristics.)
This circuit operates as a linear regulator when the
input supply (a battery) is greater than V
battery discharges below V
turns on, boosting POUT to a constant 500mV above
the linear regulator output. This configuration also
allows for true shutdown (see True Shutdown).
When the TRACK input is low, the MAX1765 operates
two independent power supplies, a DC-DC converter,
and a linear regulator. One such application of this con-
figuration is shown in Figure 4. In this mode, the device
generates two boosted voltages from a single battery
supply. The DC-DC converter could be used to supply
the power amplifier (PA) of a cell phone, while the linear
regulator powers the baseband functions within the
800mA, Low-Noise, Step-Up DC-DC Converter
______________________________________________________________________________________
LDO,
the DC-DC converter
Dual-Supply Mode
Configurations
LDO.
Track Mode
with 500mA Linear Regulator
When the
phone. Asserting TRACK switches the device into track
mode when the high-voltage supply for the PA is no
longer needed, thus improving efficiency in standby-
receive mode. When the PA again needs 5V, deassert
the TRACK input.
The MAX1765 has a shutdown mode that reduces qui-
escent current to 1µA. During shutdown, the reference,
LDO, DC-DC converter, and all feedback and control
circuitry are off. Table 2 shows the MAX1765 shutdown
truth table. If ONA, ONB, and ONL are all deasserted,
the device is shut down.
When a typical boost converter is placed into shut-
down, current can flow through the body diode of the
synchronous rectifier to the load. The MAX1765 can be
configured to allow true shutdown as shown in Figure 5.
The shutdown function is active low and is connected
to both ONA and ONL. When asserted, both the DC-DC
converter and the LDO are shut down simultaneously.
The LDO acts like a switch in this situation and discon-
nects the input from the load. Connect FBL to a resis-
tor-divider from V
Figure 3. Simple Step-Up/Step-Down Converter
SHDN
* OPTIONAL COMPONENTS
0.22µF
0.7V TO 5.5V
INPUT
ONB
ONA
CLK/SEL
ONL
REF
ILIM
REF
GND
MAX1765
to GND (R3 and R4 in Figure 5) so
FB
PGND
TRACK
POUT
OUTL
OUT
FBL
INL
LX
*
*
33µF
True Shutdown
4.7µF
Shutdown
*
V
AT 500mA
OUT
= 2.5V - 5.0V
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