MAX1534ETE+ Maxim Integrated Products, MAX1534ETE+ Datasheet - Page 9

• Manufacturer Part Number: MAX1534ETE+
• Description: IC PWR SUPPLY CONTROLLER 16TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1534ETE+

• Applications: Power Supply Controller
• Voltage - Input: 4.5 ~ 24 V
• Current - Supply: 15µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Figure 1. MAX1534 Typical Application Circuit
The MAX1534 PFM step-down topology consumes less
power than the traditional linear regulator solution when
converting from a high-input voltage source.
The MAX1534’s buck converter uses a proprietary cur-
rent-limited control scheme with operation to 100% duty
cycle. This DC-to-DC converter pulses as needed to
maintain regulation, resulting in a variable switching fre-
quency that increases with the load. This eliminates the
high supply currents associated with conventional con-
stant-frequency pulse-width-modulation (PWM) con-
trollers that switch the MOSFET unnecessarily.
When the output voltage is too low, the error comparator
sets a flip-flop, which turns on the internal P-channel
MOSFET and begins a switching cycle (Figure 2). As
shown in Figure 3, the inductor current ramps up linearly,
storing energy in a magnetic field while charging the out-
put capacitor and servicing the load. The MOSFET turns
off when the peak current limit is reached, or when the
maximum on-time of 10µs is exceeded and the output
voltage is in regulation. If the output is out of regulation
and the peak current is never reached, the MOSFET
remains on, allowing a duty cycle up to 100%. This fea-
ture ensures the lowest possible dropout voltage. Once
the MOSFET turns off, the flip-flop resets, the inductor
High-Efficiency, Triple-Output, Keep-Alive
Current-Limited Control Architecture
_______________________________________________________________________________________
V
Power Supply for Notebook Computers
OUT1
NOTE: SEE TABLE 1 FOR RECOMMENDED COMPONENT VALUES. SEE TABLE 2 FOR COMPONENT SUPPLIERS.
V
OUT2
= +3.3V ALWAYS
= +1.8V ALWAYS
100kΩ
2.2µF
Buck Converter
0.01µF
2.2µF
POK
BP
PRESET
ILIM
FB1
FB2
OUT1
OUT2
SHDN
MAX1534
GND
IN
current is pulled through D1, and the current through the
inductor ramps back down, transferring the stored ener-
gy to the output capacitor and load. The MOSFET
remains off until the 0.42µs minimum off-time expires,
and the output voltage drops out of regulation.
The MAX1534’s buck converter has an adjustable peak
current limit. Configure this peak current limit by con-
necting ILIM as shown in Table 3. Choose a current
limit that realistically reflects the maximum load current.
The maximum output current is half the peak current
limit. Although choosing a lower current limit allows
using an inductor with a lower current rating, it requires
a higher inductance (see
little to reduce inductor package size.
ILIM can be dynamically switched to achieve the high-
est efficiency over the load range. (See Buck Efficiency
vs. Load Current (Circuit 1) in the Typical Operating
Characteristics.
The MAX1534 features two 1.5Ω P-channel MOSFET
pass transistors. A P-channel MOSFET provides sever-
al advantages over similar designs using PNP pass
transistors, including longer battery life. It requires no
LDOIN
FB3
LX
V
D1
2.2µF
OUT3
10µF
V
L1
= +5V ALWAYS
IN
= +7V TO +24V
Internal P-Channel Pass Transistor
V
OUT3
C
Inductor Selection) and does
= +5V ALWAYS
OUT3
Linear Regulators
Current Limit (ILIM)
9