MAX1804EUB 데이터 시트보기 (PDF) - Maxim Integrated

부품명

상세내역

제조사

MAX1804EUB

External Four-Input Feedback Integrator for Power Supplies

Maxim Integrated 

External Four-Input Feedback Integrator for

Power Supplies

5V TO

11V

10µF

IN

OUT

OFF

MAX603

GND

SET

RBOTTOM

RTOP

100k

300k

RTOP

600k

FDV 304P

10µF

ILOAD

0 TO

500mA

1.25V

REFERENCE

2200pF

V+ SHDN SET

IN1

ADJ

IN2

MAX1804 IN3

COMP

GND

IN4

Figure 3. MAX1804 Used with Linear Regulator

inputs are disabled, OUT is high impedance. Connect

any unused input to GND.

Setting the Maximum Regulator Output

Voltage Increase

The ratio between the maximum guaranteed OUT cur-

rent of 10µA and the current in the regulator’s feedback

resistive divider determines the maximum increase. The

maximum increase in the regulator output voltage

depends on the regulator’s upper feedback resistor

(RTOP) and the sink current into OUT:

∆VOUT(MAX) = IOUT(MAX) x RTOP

The maximum adjust current IOUT(MAX) can be further

limited with a resistor (ROUT) between OUT and the

feedback point of the regulator (see Typical Operating

Circuit):

IOUT(MAX) = VFB / ROUT

where VFB is the voltage at the regulator’s feedback

point.

Therefore:

∆VOUT(MAX) = VFB x RTOP / ROUT

and:

ROUT = VFB x RTOP / ∆VOUT(MAX)

Place the regulator’s feedback resistors and ROUT

close to the regulator’s feedback pin to reduce noise

pickup at the regulator’s feedback point, which can

cause unstable switching in the regulator (Figure 5).

Shutdown Mode

SHDN is a logic input that, when held low, places the

MAX1804 in its low-power shutdown mode, reducing

the supply current to 10nA (typ). The IN1–IN4, OUT,

and ADJ are high impedance when the MAX1804 is in

shutdown or when V+ is removed. Connect SHDN to

V+ for normal operation.

Undervoltage Lockout

The MAX1804 has an undervoltage lockout (UVLO) fea-

ture that deactivates the device when the supply volt-

age at V+ goes below 2.4V; IN1–IN4, OUT, and ADJ go

to high impedance and do not affect the regulator oper-

ation. Hysteresis holds the device in lockout until the

supply voltage at V+ rises above 2.6V.

Integrator Gain-Bandwidth Product

and Regulator Stability

The MAX1804 gain-bandwidth (GBW) product is set by

the external capacitor on COMP:

GBW = [4 x (IN_ transconductance)] / (2π ✕ CCOMP)

The bandwidth is typically 40kHz with a 470pF capaci-

tor on COMP.

For system stability, the integrator GBW product is typi-

cally set below the regulator circuit’s crossover frequen-

cy, if known. Switching regulators typically have

crossover frequencies well below their switching frequen-

cies. Setting the MAX1804’s GBW product too high can

cause regulator loop instability, typically evidenced by

ringing after transients. Setting the GBW product unnec-

essarily low will slow the MAX1804’s loop response to

transients, although the regulator’s loop transient

response will remain unaffected (see Load Transient

Response in Typical Operating Characteristics).

Often the regulator’s crossover frequency varies with

load and is not easily found. If the regulator’s crossover

frequency is unknown, the MAX1804’s gain-bandwidth

product can be chosen empirically. Start with a fairly

low capacitor value (470pF is a good starting point)

and increase the value until the circuit is stable with all

loads. Then increase the value further to ensure design

margin. If transient response is unimportant, choose a

large COMP capacitor value (such as 2200pF), thereby

maximizing stability.

8 _______________________________________________________________________________________

Share Link: