© 2008 Microchip Technology Inc. DS22114A-page 11
MCP9509/10
4.0 FUNCTIONAL DESCRIPTION
The MCP9509/10 integrates a temperature switch with
a user programmable threshold. The temperature
switch threshold or alert limit is programmed using an
external resistor R
SET
. A logic signal is asserted when
the die temperature crosses the programmed alert
limit. The MCP9509 has an Open-Drain output which
requires an external pull-up resistor for operation. The
MCP9510 output can be configured to three user
selectable output configurations. The OUTSET pin is
used to select Active-Low Push-Pull, Active-Low
Open-Drain (with internal 100 kΩ pull-up resistor),
Active-High Push-Pull output configurations. In addi-
tion, this device provides user selectable hysteresis of
2°C and 10°C (typical).
4.1 SET Input Pin
The SET input pin is used to connect an external
resistor R
SET
. The resistor sets the alert threshold. The
SET pin outputs a constant current I
SET
(~5 µA) to bias
R
SET
(Shown in Figure 4-1). The voltage across R
SET,
V
SET,
is compared to an internal thermal diode.
FIGURE 4-1: SET input.
When the thermal diode voltage exceeds V
SET
, the
sensor output asserts. The assert polarity is
determined by the state of the OUTSET pin.
4.2 MCP9510 OUTSET Input Pin
This pin is used to select the device output configura-
tion. This feature enables in-circuit device output con-
figuration by driving this pin with a microcontroller I/O
pin to Output-HIGH, Output-LOW, or High-Impedance
input. Figure 4-4 shows the configuration and output
conditions.
The input structure of this pin consists of a resistor lad-
der and comparators to determine OUTSET level
threshold. Figure 4-2 shows the circuit configuration.
The OUTSET input resistance must be carefully
considered for leakage current when connecting volt-
age source to change output configuration.
FIGURE 4-2: MCP9510 OUTSET Input
Structure.
The OUTSET pin input impedance Z
OUTSET
is set by
the internal resistance R
A
= 1 MΩ (typical). The input
structure is a voltage divider network from V
DD
.
Therefore, the leakage current on the OUTSET pin is a
function of change in V
DD
and the V
OSET
.
4.3 HYST Input Pin (Hysteresis Select)
The MCP9509/10 family has a user selectable
hysteresis input pin HYST. Hysteresis can be externally
selected to either 2°C (HYST = GND) or 10°C
(HYST = V
DD
). Figure 4-3 shows graphical description
of change in hysteresis.
For example, if the alert temperature threshold is set to
T
SET
= 100°C (R
SET
= 16.1 kΩ) with an Active-Low out-
put configuration, the output asserts Low when temper-
ature exceeds 100°C ± T
ACY
. The output remains
asserted Low until temperautre falls below T
HYST
, 98°C
(HYST = GND) or 90°C (HYST = V
DD
).
FIGURE 4-3: Output Hysteresis.
SET
R
SET
V
SET
I
SET
R
x
+
-
OUT/
OUT
Thermal
Diode
V
DD
+
-
-
+
OUTSET
Pin
R
A
R
A
R
1
R
2
R
3
MCP9510
Cold
Hot
T
SET
T
HYST
Temperature
V
OUT
10°C Typical Hysteresis
2°C Typical
Hysteresis
