rt9591 Richtek Technology Corporation, rt9591 Datasheet - Page 11

• Manufacturer Part Number: rt9591
• Description: Smart Photoflash Capacitor Charger With Igbt Driver
• Manufacturer: Richtek Technology Corporation

Adjustable Input Current
The RT9591 simply adjusts peak primary current by a
resistor R
Block Diagram. R
determines the ON time of primary NMOS.
During the ON time, the primary current ramps linearly
with a slope = V
resister (R
Where I
ratio of transformer.
Users could select appropriate R
capability and required charging time.
Minimum I
where 430 x 10
time.
If lower I
transformer to incease N x L
DS9591-07 August 2007
Ra
R
The
CS
=
=
I
PK
(I
1M
1M
PK
PK-PRI
PK-PRI
-
PRI
Input Average Current & Output Voltage
CS
-
x
−
CS
PRI
PK-PRI
Ra
Ra
setting
) could be
connecting to CS pin as shown in Function
is the primary peak current and N is the turns
setting limitation is required, you may change
−
30
BAT
8
-9
(
Ω
CS
x
x
Limitation
is the maximum value of minimum off
/L
)
10
must
10
paralleled with internal 1MΩ resistor
PRI
-3
-
.
12
calculated as:
Consequently, the current setting
x
Figure 7
N)
≥
Time (1s/Div)
430
PRI
x
L
product.
CS
PRI
x
N
according to the battery
10
x
-9
L
PRI
x V
OUT
V
C
,
BAT
IN
= 10uF
= 3.3V
Preliminary
Patent Pending
Adjustable Output Voltage
The RT9591 senses output voltage by a voltage divider
connecting to the anode of the rectifying diode during OFF
time. This eliminates power loss at voltage-sensing
circuit when charging completed. R3 to (R1+R2) ratio
determines the output voltage as shown in the application
circuit Figure1. The feedback reference voltage
If V
Application according to the following equation:
R3 is recommend 1KΩ; R1 and R2 are used 150KΩ for
reducing parasitic capacitance coupling effect of FB pin.
R1 and R2 MUST be greater than 0805 size resister for
enduring secondary HV.
Lower Charging Current at Low Battery Voltage
The RT9591 integrates a voltage detector with open drain
output. This voltage detector is specially designed for
lowering peak primary current and minimizing the impact to
battery voltage at low V
The voltage detector senses V
R6 and R7 and compares it with internal 1V reference
voltage. When the sensed voltage is lower than the
reference voltage, VDOUT pin goes low and changes the
resistance connecting to CS pin and the ON time. For
example, if R6 equal 1.5MΩ and R7equal 1MΩ, VDOUT
pin change status form open to ground when V
under 2.5V. And current setting resister R4 and R5 can
set different resistance for different input current when V
voltage under detector voltage. Figure 9 shows the lower
charging current waveform. When V
the input average current become approximately 600mA
to 460mA.
V
OUT
OUT
=
= V
300V, in Figure 1 Photoflash Capacitor Charger
FB
×
(1+
R1+ R2
R3
BAT
condition as shown in Figure 8.
), so
BAT
through a resister divider
BAT
R1+ R2
R3
voltage under 2.5V,
RT9591
www.richtek.com
= 305
BAT
is 0.98V.
voltage
BAT
11