RT9807 RICHTEK [Richtek Technology Corporation], RT9807 Datasheet - Page 5

• Manufacturer Part Number: RT9807
• Description: Micro-Power Voltage Detector with Manual Reset
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Application Information
The RT9807 provides adjustable reset delay time to fit
the need of a variety of μP applications. The reset delay
time of the RT9807
capacitor between the CT pin and GND. The CT capacitor
must fit the need of low-leakage (<10nA), and it is
recommended to use a ceramic capacitor such as X7R or
NPO type.
Reset Delay Time Setting
When the VDD voltage exceeds
a current source will start to charge the CT capacitor and
the CT voltage will rise. When the CT voltage exceeds
0.65V, the RST voltage will change from low to high.
Therefore, there is a delay time between the point of VDD
reaching its threshold voltage and the RST active-high
point. The delay time can be calculated according to the
following equation.
Operating with a Voltage Divider
The voltage detector monitors the V
a reset signal when V
The detecting level is determined by an external resistive
voltage divider.
DS9807-01 April 2011
t
V
V
DELAY
CC_TH
CC_HYS
VDD Voltage
RST Voltage
( s) =
μ
= V
V
= V
CT
TH
Delay Time
HYS
0.18 x 10 x C
x 1 +
⎛
⎜
⎝
Figure 1. Delay Time
x 1 +
⎛
⎜
⎝
CC
can be adjusted by connecting a
R2
R1
is higher than the detecting level.
0.58
6
R2
R1
⎞
⎟
⎠
, V
⎞
⎟
⎠
CT
TH
the VDD threshold voltage,
( F)
: Threshold Voltage.
μ
CC
voltage to generate
+ 220
VDD Threshold
Voltage
GND
0.65V
GND
GND
RST Voltage
The rising and falling of the VCC and RST voltage can be
explained in five steps as shown in the following diagram.
1. RST voltage is pulled up to VCC voltage.
2. When the VCC voltage is down to the detector threshold
3. When the VCC voltage is lower than minimum operating
4. RST voltage becomes low level.
5. When the VCC voltage exceeds the threshold voltage
VCC
voltage (Point A), RST voltage becomes low level.
voltage, the RST voltage is indefinite. In the case of
open drain type, RST voltage is equal to pull-up voltage.
(Point B), the internal source current will start to charge
CT capacitor. The RST voltage will go high after a delay
time when the CT capacitor voltage reaches 0.65V.
1
A
V
CC
Drop Reset
Delay Time
R1
R1
2
Figure 3. Operation Diagram
Figure 2. Voltage Divider
Hysteresis
VDD
GND
range
RT9807
3
R
RST
CT
4
Minimum Operation Voltage
V
CC_TH
B
C
5
RT9807
CT
www.richtek.com
Power-On Reset
Delay Time
– Hysteresis Voltage
V
GND
GND
CC_TH
5