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MAX1598

Low-Noise, Low-Dropout, 200mA Linear Regulator

Maxim Integrated 

Low-Noise, Low-Dropout, 200mA

Linear Regulator

Output Voltage

The MAX1598 is supplied with factory-set output voltages

from 2.5V to 5V in 100mV increments. Except for the

MAX1598EZK29 and the MAX1598EZK32 (which have an

output voltage preset at 2.84V and 3.15V, respectively),

the two-digit suffix allows the customer to choose the out-

put voltage in 100mV increments. For example, the

MAX1598EZK33 has a preset output voltage of 3.3V (see

the Selector Guide).

Internal P-Channel Pass Transistor

The MAX1598 features a 1.1Ω typical P-channel MOSFET

pass transistor. This provides several advantages over

similar designs using PNP pass transistors, including

longer battery life. The P-channel MOSFET requires no

base drive, which reduces quiescent current consider-

ably. PNP-based regulators waste considerable current in

dropout when the pass transistor saturates. They also use

high base-drive currents under large loads. The

MAX1598 does not suffer these problems and consumes

only 100µA of quiescent current whether in dropout, light-

load, or heavy-load applications (see the Typical

Operating Characteristics).

Current Limit

The MAX1598 includes a current limiter, which monitors

and controls the pass transistor’s gate voltage, limiting the

output current to 458mA. For design purposes, consider

the current limit to be 220mA minimum to 1.1A maximum.

The output can be shorted to ground indefinitely without

damaging the part.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX1598. When the junction temperature

exceeds TJ = +155°C, the thermal sensor signals the

shutdown logic, turning off the pass transistor and

allowing the IC to cool. The thermal sensor turns the

pass transistor on again after the IC’s junction tempera-

ture cools by 15°C, resulting in a pulsed output during

continuous thermal-overload conditions.

Thermal-overload protection is designed to protect the

MAX1598 in the event of fault conditions. For continual

operation, do not exceed the absolute maximum junc-

tion-temperature rating of TJ = +150°C.

Operating Region and Power Dissipation

The MAX1598 maximum power dissipation depends on

the thermal resistance of the case and circuit board, the

temperature difference between the die junction and

ambient air, and the rate of air flow. The power dissipation

across the device is P = IOUT (VIN - VOUT). The maximum

power dissipation is:

PMAX = (TJ - TA) / (θJB + θBA)

where TJ - TA is the temperature difference between the

MAX1598 die junction and the surrounding air, θJB (or

θJC) is the thermal resistance of the package, and θBA

is the thermal resistance through the PC board, copper

traces, and other materials to the surrounding air.

The GND pin of the MAX1598 performs the dual func-

tions of providing an electrical connection to ground

and channeling heat away. Connect the GND pin to

ground using a large pad or ground plane.

Reverse Battery Protection

The MAX1598 has a unique protection scheme that limits

the reverse supply current to 1mA when either VIN or

V SHDN falls below ground. Their circuitry monitors the

polarity of these two pins and disconnects the internal

circuitry and parasitic diodes when the battery is

reversed. This feature prevents device damage.

Noise Reduction

An external 0.01µF bypass capacitor at BP, in conjunc-

tion with an internal 200kΩ resistor, creates an 80Hz

lowpass filter for noise reduction. The MAX1598 exhibits

30µVRMS of output voltage noise with CBP = 0.01µF and

COUT = 10µF. This is negligible in most applications.

Startup time is minimized by a power-on circuit that pre-

charges the bypass capacitor. The Typical Operating

Characteristics section shows graphs of Noise vs. BP

Capacitance, Noise vs. Load Current, and Output Noise

Spectral Density.

____________Applications Information

Capacitor Selection and

Regulator Stability

Under normal conditions, use a 1µF capacitor on the

MAX1598 input and a 2.2µF to 10µF capacitor on the out-

put. Larger input capacitor values and lower ESRs pro-

vide better supply-noise rejection and line-transient

response. Reduce noise and improve load-transient

response, stability, and power-supply rejection by using

large output capacitors. For stable operation over the full

temperature range and with load currents up to 200mA, a

2.2µF (min) ceramic capacitor is recommended.

Note that some ceramic dielectrics exhibit large capaci-

tance and ESR variation with temperature. With

dielectrics such as Z5U and Y5V, it may be necessary to

increase the capacitance by a factor of 2 or more to

ensure stability at temperatures below -10°C. With X7R or

X5R dielectrics, 2.2µF should be sufficient at all operating

temperatures. A graph of the Region of Stable COUT ESR

vs. Load Current is shown in the Typical Operating

Characteristics.

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