Rainbow Electronics MAX1804 - Manual (Page 6)

MAX1804
External Four-Input Feedback Integrator for
Power Supplies
6 _______________________________________________________________________________________
Detailed Description
The MAX1804 is a precision external feedback integra-
tor used for tight point-of-load regulation in power-man-
agement systems. The dynamic regulation of the output
is still controlled by the power-supply regulator. The
MAX1804 is used only to fine tune the output voltage,
removing load- and line-regulation errors and voltage
drops across switches and connectors that occur in the
power-supply distribution line.
The MAX1804 includes four remote-sense inputs and
an output that connects to a voltage regulator’s feed-
back divider. It can be used with any regulator or con-
troller with a high-impedance feedback input. Its OUT
pin sinks current to increase the regulator’s set point so
that the four IN_ inputs are at or above MAX1804’s reg-
ulation set point, which is four times the voltage applied
to the ADJ pin. The MAX1804 monitors the input signals
and compares the lowest to the voltage set point. The
error between the input signal and the set point is inte-
grated. The MAX1804 output stage generates a current
based on the integrator output to adjust the regulator’s
output voltage to meet the set point.
Pin Description
NAME PIN FUNCTION
IN1 1
Sense Input 1. Connect to one of up to four inputs to be monitored. If IN_ is the lowest active input,
IN_ will be regulated at 4 x V
ADJ . If IN_ is less than 90% of the regulation set point (4 x VADJ), it is
automatically disabled.
IN2 2 Sense Input 2
IN3 3 Sense Input 3
IN4 4 Sense Input 4
ADJ 5
Regulation Adjustment Input. The voltage at this input adjusts the regulation set point of
IN1–IN4.There is a 4x scale factor between V
ADJ and the regulation set point.
GND 6 Ground
COMP 7
Integrator Capacitor Connection. Connect a capacitor (>100pF) to GND to set the integrator time
constant. See Integrator Gain-Bandwidth Product and Regulator Stability section.
OUT 8
O p en- D r ai n O utp ut. C an si nk at l east 10 µ A i f any of the i np uts r em ai n b el ow the r eg ul ati on set p oi nt.
C onnect OU T to the feed b ack p oi nt of the r eg ul ator - d i vi d er r esi stor s. If OU T i s connected thr oug h a
r esi stor , i ts val ue r el ati ve to the r eg ul ator ’ s feed b ack- d i vi d er val ues sets the m axi m um p osi ti ve
ad j ustm ent r ang e. S ee S etti ng the M axi m um Reg ul ator O utp ut Ad j ustm ent Incr ease secti on.
SHDN 9
Shutdown Control Input. When SHDN is low, the device is off and the supply current is reduced to
about 10nA. All inputs are in high-impedance state. When SHDN is high, the device is on.
V+ 10 Power-Supply Input. Bypass with 0.1 µF capacitor to GND.
Figure 1. Test Circuit for MAX1804 IN_ Regulation Set Point
0.1 µF
1M
1%
3.3V
3.3V
1k
1%
+10V
-10V
1k
1%
75k
1%
25k
1%
470pF
ADJ
COMP
EXTERNAL
REF
IN2
IN3
IN4
IN1
V+
OUT
MAX1804
MAX400
SHDN