adm1203 Analog Devices, Inc., adm1203 Datasheet - Page 4

• Manufacturer Part Number: adm1203
• Description: Simple Tracker? With Circuit Breaker
• Manufacturer: Analog Devices, Inc.

ADM1203
ENABLING A SINGLE SUPPLY
The ADM1203 requires a supply voltage of 2.7V to 16.5V on its
Vcc pin for operation. The device may be powered from the
input supply rail that is being switched or from an auxiliary
supply.
An internal charge pump ensures that the ADM1203 is capable
of fully enhancing an external FET via the GATE pin, turning
on the output. An external capacitor may be required on the
GATE node for stability.
Power up can be externally initiated by driving the
UP/DOWNb (ADM1203-1) or UP/STOPb (ADM1203–2)
logic pin high. A low on this pin will initiate a power down.
The V
A single ADM1203 device may be used where a single supply
rail is required to switch on at a controlled slew rate (see Figure
1). The value of the slew rate capacitor, C
slew rate of the GATE voltage at startup. An internal current
10µA source charges C
the same rate.
MULTI-SUPPLY TRACKING
The primary function of the ADM1203 is to provide a voltage
tracking solution for multiple supply rails. The implementation
in Figure 2 will provide this function. Each voltage rail has its
own ADM1203 device driving a FET.
The UP/DOWNb (ADM1203-1/3) or UP/STOPb (ADM1203-
2/4) pins of all devices can be driven by a single logic input
which will initiate a system power-up going high or power-
down going low.
In figure 2, the ADM1203 is configured to control the ramp of
the largest supply first. The output of the first device is
connected to the slew pin on the second device to allow the rate
of the first supply to control the rate of the second and so on.
POWER ON/OFF
3.3VIN
OUTFB
Figure 1. ADM1203 Switching on a Single Supply
C
pin monitors the output voltage.
SLEW
C
TIMER
SLEW
C
C
UP/STOP
V
SLEW
TIMER
cc
and the GATE voltage is ramped at
ADM1203-2
R
s
GND
RS-
GATE
V
OUT
SLEW
Q 1
, will dictate the
3.3VOUT
Rev. PrD | Page 4 of 8
A low-to-high transition on the UP/DOWNb or UP/STOPb pin
will initiate turn-on of the supplies. The ADM1203 will begin to
source current into the C
GATE pins will begin to rise, or “track” up, at the same rate, as
set by the value of C
100mV of the C
potentials.
A high-to-low on the UP/DOWNb pin of the ADM1203-1 will
initiate a tracking down of the supply rails. The voltages will
attempt to stay with ~100mV of each other assuming the load
current will be sufficient to discharge the capacitors at the
required rate. (See Figure 3.)
A high-to-low on the UP/STOPb pin of the ADM1203-2 will
initiate an emergency fast shutdown of all supply rails
simultaneously. (See Figure 4.) Note that while the pass FETs
will be turned off immediately the actual discharge rate of each
supply rail will depend on the load.
POWER ON/OFF
POWER ON/OFF
2.7VIN
3.3VIN
5VIN
POWER ON/OFF
Figure 2. ADM1203 Solution for Tracking 3 Supplies
C
SLEW
SLEW
Preliminary Technical Data
SLEW
voltage until they level off at their full
C
C
C
TIMER
TIMER
. All supply voltages will remain within
TIMER
SLEW
SLEW
SLEW
TIMER
TIMER
UP/DOWN
UP/DOWN
SLEW
TIMER
UP/DOWN
ADM1203-1
ADM1203-1
V
V
ADM1203-1
V
cc
capacitor. The voltages on all
cc
cc
R
R
R
S
GND
S
GND
S
GND
RS-
RS-
V
V
RS-
OUTFB
V
OUTFB
GATE
GATE
OUTFB
GATE
1nF
1nF
1nF
Q 1
Q 1
Q 1
2.7VOUT
3.3VOUT
5VOUT