MAX776CSA+ Maxim Integrated Products, MAX776CSA+ Datasheet - Page 10

• Manufacturer Part Number: MAX776CSA+
• Description: DC DC Cntrlr Single-OUT Inverting 3V to 16.5V Input 8-Pin SOIC N
• Manufacturer: Maxim Integrated Products
• Type: Invertingr

Specifications of MAX776CSA+

• Package: 8SOIC N
• Input Voltage: 3 to 16.5 V
• Output Voltage: -15 V
• Output Current: 0.4 A
• Number Of Outputs: 1
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8 Narrow
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

the current limit for the first two pulses is set to one-half
the peak current limit. If those pulses bring the output
voltage into regulation, the voltage comparator keeps
the MOSFET off, and the current limit remains at one-half
the peak current limit. If the output voltage is out of
regulation after two consecutive pulses, the current limit
-5V/-12V/-15V or Adjustable, High-Efficiency,
Low I
Figure 2. Bootstrapped Connection Using Fixed Output
Voltages
Figure 3. Bootstrapped Connection Using External Feedback
Resistors
10
150 F
NOTE: Si9435 HAS V
C1
150 F
V
V
IN
IN
______________________________________________________________________________________
C1
PRODUCT
MAX774
MAX775
MAX776
0.1 F
0.1 F
C2
0.1 F
Q
C3
C3
R2
R1
GS
C2
0.1 F
OF 20V MAX
Inverting DC-to-DC Controllers
VOLTAGE (V)
1
3
2
4
OUTPUT
1
3
2
4
OUT
SHDN
FB
REF
-12
-15
-5
OUT
SHDN
FB
REF
MAX774
MAX775
MAX776
GND
MAX774
MAX775
MAX776
GND
8
*
VOLTAGE (V)
8
MAX775, MAX776 = 120 F, 20V
MAX774 = 330 F, 10V
INPUT
3 to 15
EXT
3 to 8
3 to 5
CS
V+
*
MAX775, MAX776 = 120 F, 20V
EXT
MAX774 = 330 F, 10V
CS
V+
5
6
7
22 H
5
6
7
22 H
L1
L1
CURRENT (A)
P
Q1
Si9435
R1
0.07
OUTPUT
1N5822/
MBR340
P
Q1
Si9435
R3
0.07
1N5822/
MBR340
0.5
0.4
1
C4
*
V
OUT
V
C4
OUT
*
for the next pulse will equal the full current limit.
With heavy loads, the MOSFET first switches twice at
one-half the peak current value. Subsequently, it stays
on until the switch current reaches the full current limit,
and then turns off. After it is off for 2.3µs, the MOSFET
switches on once more, and remains on until the switch
current again reaches its limit. This cycle repeats until
the output is in regulation.
A benefit of this control scheme is that it is highly effi-
cient over a wide range of input/output ratios and load
currents. Additionally, PFM converters do not operate
with constant-frequency switching, and have relaxed
stability criterion (unlike PWM converters). As a result,
their external components require smaller values.
With PFM converters, the output voltage ripple is not
concentrated at the oscillator frequency (as it is with
PWM converters). For applications where the ripple fre-
quency is important, the PWM control scheme must be
used. However, for many other applications, the smaller
capacitors and lower supply current of the PFM control
scheme make it the better choice. The output voltage
ripple with the MAX774/MAX775/MAX776 can be held
quite low. For example, using the circuit of Figure 2,
only 100mV of output ripple is produced when generat-
ing a -5V at 1A output from a +5V input.
Figures 2 and 3 are the standard application circuits
for bootstrapped mode, and Figure 4 is the circuit for
nonbootstrapped mode. Since EXT is powered by OUT,
using bootstrapped or nonbootstrapped mode will
directly affect the gate drive to the FET. EXT swings
from V+ to V
Figure 4. Nonbootstrapped Operation (V
150 F
V
IN
C1
C2
0.1 F
R2
OUT
R1
C3
0.1 F
. In bootstrapped operation, OUT is
Nonbootstrapped Operation
1
3
2
4
OUT
SHDN
FB
REF
MAX774
MAX775
MAX776
GND
8
*
MAX775, MAX776 = 120 F, 20V
MAX774 = 330 F, 10V
EXT
Bootstrapped vs.
CS
V+
IN
5
6
7
22 H
> 4.5V)
L1
P
Q1
Si9435
R3
0.07
1N5822/
MBR340
C4
*
V
OUT