adm1051a Analog Devices, Inc., adm1051a Datasheet - Page 7

• Manufacturer Part Number: adm1051a
• Description: Precision Dual Voltage Regulator Controllers
• Manufacturer: Analog Devices, Inc.

For compatibility with the TYPEDET signal, the regulator output
voltage of Channel 1 may be selected using the Shutdown pin.
This is a multilevel, dual-function input that allows selection of
the regulator output voltage as well as shutdown of the regulator.
By setting SHDN1 to different voltages, the regulator can be put
into four different operating modes.
SHDN1 Voltage
< 0.8 V
2 V–3.9 V
4.3 V–5.3 V
>6.2 V or Floating
If the SHDN1 pin is connected to a voltage less than 0.8 V, the
FORCE output will go low and the regulator will be shut down.
If the SHDN1 pin is connected to a voltage greater than 6.2 V,
or simply left open-circuit, the regulator will operate normally
and provide 1.5 V out. This allows the regulator to operate
normally with no external connection to SHDN1.
If the SHDN1 pin is connected to a voltage between 2 V and 3.9 V,
the regulator will also operate normally and provide 1.5 V out.
If the SHDN1 pin is connected to a voltage between 4.3 V and
5.3 V, the FORCE output will be high and the external MOSFET
will be turned hard on, making the output voltage equal to the 3.3 V
input (less any small drop due to the on-resistance of the MOSFET).
In this mode it is not actually regulating, but simply acting as a
switch for the 3.3 V supply. The voltage drop across the Channel 1
MOSFET in Mode 3 can be minimized by using a MOSFET
with very low on resistance, for which Channel 1 is optimized,
such as the PHD55N03LT.
The latter two modes allow the regulator to be controlled by the
TYPEDET signal simply by using potential divider, as shown in
Figure 2.
Table I. Shutdown Functionality for 1.5 V Channel
OUTPUT CURRENT
OUTPUT VOLTAGE
MOSFET DRAIN
GATE DRIVE TO
OR CHANNEL 2
OR CHANNEL 2
TO EXTERNAL
3.3V SUPPLY
12V SUPPLY
CHANNEL 1
CHANNEL 1
EXTERNAL
MOSFET
Mode Function
1
2
3
4
V
POR THRESHOLD
Force Output Low, Regulator
Shutdown
1.5 V Output
Force Output High, V
1.5 V Output
REF
THRESHOLD
MOSFET GATE
TURN-ON
THRESHOLD
4V – 7V
OUTPUT VOLTAGE
HOLD-OFF TIME
HICCUP MODE
OUT
2 AMPS
NORMAL
= 3.3 V
A shutdown function can be added by connecting an open-drain/
open-collector logic output to SHDN1, or by using a totem-pole
logic output with a Schottky diode, as shown in Figure 3.
When the logic output is high or turned off, the regulator mode
will be controlled by TYPEDET. When the logic output is low,
the regulator will be shut down.
TYPEDET
X
0
1
X = Don’t care.
Note that when Channel 1 of the ADM1051 is set to 3.3 V,
Channel 2 should not be shut down while Channel 1 is active.
DEVICE ENTERS HICCUP MODE
OUTPUT < 0.8
Table II. TYPEDET and Shutdown Truth Table
COMPLEMENTARY
OR TOTEM-POLE
OUTPUT
EN
EN
OPEN-DRAIN OR
OPEN-COLLECTOR
OUTPUT
1:40 DUTY CYCLE
FAULT CURRENT
OFF
V
SCHOTTKY
REG
DIODE
TYPEDET
ON
TYPEDET
TYPEDET
EN
0
1
1
SHDN1
ADM1051/ADM1051A
PC 5V SUPPLY
3k
3k
PC 5V SUPPLY
PC 5V SUPPLY
3k
3k
3k
3k
SHDN1
FAULT
REMOVED
Regulator Mode
Shutdown
1.5 V
3.3 V
SHDN1
SHDN1
ADM1051A
ADM1051A
ADM1051/
ADM1051/