capacitors to reduce noise and improve load-transient

response, stability, and power-supply rejection.

The output capacitor’s equivalent series resistance

(ESR) affects stability and output noise. Use output

capacitors with an ESR of 30m

Ω or less to ensure sta-

bility and optimize transient response. Surface-mount

ceramic capacitors have very low ESR and are com-

mize the impact of PC board trace inductance.

Noise, PSRR, and Transient Response

The MAX1589A is designed to operate with low dropout

voltages and low quiescent currents in battery-powered

systems, while still maintaining good noise, transient

response, and AC rejection. See the Typical Operating

Characteristics for a plot of Power-Supply Rejection

Ratio (PSRR) vs. Frequency. When operating from noisy

sources, improved supply-noise rejection and transient

response can be achieved by increasing the values of

the input and output bypass capacitors and through

passive filtering techniques.

The MAX1589A load-transient response (see the

Typical Operating Characteristics) shows two compo-

nents of the output response: a near-zero DC shift from

the output impedance due to the load-current change,

and the transient response. A typical transient response

for a step change in the load current from 100mA to

500mA is 35mV. Increasing the output capacitor’s value

and decreasing the ESR attenuates the overshoot.

Input-Output (Dropout) Voltage

A regulator’s minimum input-output voltage difference

(dropout voltage) determines the lowest usable supply

voltage. In battery-powered systems, this determines

the useful end-of-life battery voltage. Because the

MAX1589A uses a p-channel MOSFET pass transistor, its

dropout voltage is a function of drain-to-source on-resis-

Ω) multiplied by the load current

(see the Typical Operating Characteristics):

The MAX1589A ground current reduces to 70µA in

dropout.

Chip Information

TRANSISTOR COUNT: 2556

PROCESS: BiCMOS

Low-Input-Voltage, 500mA LDO Regulator

with

R

RE

ES

SE

ET

8

_______________________________________________________________________________________

Figure 2. Power Operating Regions for 6-Pin SOT23: Maximum

Output Current vs. Input Voltage

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

(POWER DISSIPATION LIMIT)

2.5

2.0

1.5

1.0

0.5

03.0

MAXIMUM RECOMMENDED

OUTPUT CURRENT 6-PIN SOT23

°C

°C

100

200

300

400

500

600

0

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

(POWER DISSIPATION LIMIT)

2.5

2.0

1.5

1.0

0.5

03.0

MAXIMUM RECOMMENDED

OUTPUT CURRENT 6-PIN TDFN

°C

100

200

300

400

500

600

0

Figure 3. Power Operating Region for 6-Pin TDFN: Maximum

Output Current vs. Input Voltage