Datasheet
Low-Battery Detector
The low-battery detector compares the voltage on LBR
with the internal 1.31V reference. The output, LBD, is an
open-drain N-channel MOSFET. In addition to detecting
and warning of a low battery voltage, the comparator
can also perform other voltage-monitoring operations
such as power-failure detection.
Another use of the low-battery detector is to lower the
oscillator frequency when the input voltage goes below
a specified level. Lowering the oscillator frequency
increases the available output power, compensating for
the decrease in available power caused by reduced
input voltage (see Figure 5).
Logic-Level Shutdown Input
The shutdown mode is entered whenever I
C
(pin 6) is
driven below 0.2V or left floating. When shut down, the
MAX630’s analog circuitry, oscillator, L
X
, and LBD out-
puts are turned off. The device’s quiescent current dur-
ing shutdown is typically 10nA (1µA max).
Bootstrapped Operation
In most circuits, the preferred source of +V
S
voltage for
the MAX630 and MAX4193 is the boosted output volt-
age. This is often referred to as a “bootstrapped” oper-
ation since the circuit figuratively “lifts” itself up.
The on-resistance of the N-channel L
X
output decreas-
es with an increase in +V
S
; however, the device operat-
ing current goes up with +V
S
(see the Typical
Operating Characteristics, I
S
vs. +V
S
graph). In circuits
with very low output current and input voltages greater
than 3V, it may be more efficient to connect +V
S
direct-
ly to the input voltage rather than bootstrap.
MAX630/MAX4193
CMOS Micropower Step-Up
Switching Regulator
_______________________________________________________________________________________ 5
COMP 2
+5V INPUT
R3
169kΩ
R4
100kΩ
L1
470
LOW BATTERY INPUT
1.31V
OSC
R
ON
≅ 3Ω
40kHz
COMP 1
1.31V
BANDGAP
REFERENCE
AND
BIAS GENERATOR
1 LBR
2C
X
3L
X
4 GND
D1
1N4148
+V
S
5
I
C
6
V
FB
7
LBD 8
LOW-BATTERY OUTPUT
(LOW IF INPUT < 3V)
C
C
R1
499kΩ
R2
47.5kΩ
SHUTDOWN
OPERATE
+15V OUTPUT
20mA
C1
470μF
25V
MAX630
COMP 2
Figure 1. +5V to +15V Converter and Block Diagram