MAX1673 Datasheet, PDF (6/8 Pages) Maxim Integrated Products – Regulated, 125mA-Output, Charge-Pump DC-DC Inverter

Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter
______________________________________________________________Pin Description
PIN
NAME
FUNCTION
Regulation-Mode Select Input. Driving LIN/SKIP high or connecting it to IN selects LIN mode, with regula-
1
LIN/SKIP tion accomplished by modulating switch resistance. Driving LIN/SKIP low or connecting it to GND selects
Skip mode, where the device regulates by skipping charge-pump pulses.
2
CAP+ Positive Terminal of Flying Capacitor
3
CAP- Negative Terminal of Flying Capacitor
4
SHDN
Shutdown Control Input. Drive SHDN low to shut down the MAX1673. Connect SHDN to IN for normal
operation. OUT connects to GND through a 1Ω (typical) resistor in shutdown mode.
5
OUT
Inverting Charge-Pump Output
6
FB
Feedback Input. Connect FB to a resistor-divider from IN (or other reference source) to OUT for regulated
output voltages (Figures 1 and 4).
7
GND
Ground
8
IN
Power-Supply Positive Voltage Input
Detailed Description
The MAX1673 new-generation, high-output-current,
regulated charge-pump DC-DC inverter provides up to
125mA. Designed specifically for compact applica-
tions, a complete regulating circuit requires only three
small capacitors and two resistors. The MAX1673
employs On-Demand™ regulation circuitry, providing
output regulation modes optimized for either lowest out-
put noise or lowest supply current. In addition, the
MAX1673 includes shutdown control.
INPUT
5.0V
ON
C_IN
10µF
OFF
C_FLY
2.2µF
LIN
SKIP
R1
8
100k
4 _SHDN IN
6
FB
2 _{CAP+ MAX1673}
R1
60.4k
5
OUT
3
CAP-
C_OUT
22µF
1 _LIN/SKIP
GND
7
OUTPUT
-3V
In Linear (LIN) mode or when heavily loaded in Skip
mode, the charge pump runs continuously at 350kHz.
During one-half of the oscillator period, switches S1 and
S2 close (Figure 2), charging the transfer capacitor
(C_FLY) to the input voltage (CAP- = GND, and CAP+ =
IN). During the other half cycle, switches S3 and S4
close (Figure 3), transferring the charge on C_FLY to the
output capacitor (CAP+ = GND, CAP- = OUT).
S1
IN
CAP+ S3
S2
C_FLY
S4
C_OUT
OUT
CAP-
350kHz
Figure 2. Charging C_FLY
S1
IN
CAP+ S3
S2
C_FLY
S4
C_OUT
OUT
CAP-
350kHz
Figure 1. Standard Application Circuit
Figure 3. Transferring Charge on C_FLY to C_OUT
6 _______________________________________________________________________________________