UCC3941-5 Datasheet PDF - Unitrode
| Part Number | UCC3941-5 | |
| Description | (UCCx941-x) 1V Synchronous Boost Converter | |
| Manufacturers | Unitrode | |
| Logo |  |
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1V Synchronous Boost Converter
application
INFO
available
UCC2941-3/-5/-ADJ
UCC3941-3/-5/-ADJ
FEATURES
• 1V Input Voltage Operation Startup
Guaranteed Under Full Load on Main
Output With Operation Down to 0.4V
• Input Voltage Range of 1V to VOUT +
0.5V
• 500mW Output Power at Battery
Voltages as Low as 0.8V
• Secondary 9V Supply From a Single
Inductor
• Adjustable Output Power Limit Control
• Output Fully Disconnected in
Shutdown
• Adaptive Current Mode Control for
Optimum Efficiency
• 8µA Shutdown Supply Current
DESCRIPTION
The UCC3941 family of low input voltage single inductor boost converters
are optimized to operate from a single or dual alkaline cell, and step up to
a 3.3V, 5V, or an adjustable output at 500mW. The UCC3941 family also
provides an auxiliary 9V 100mW output, primarily for the gate drive supply,
which can be used for applications requiring an auxiliary output such as a
5V supply by linear regulating. The primary output will start up under full
load at input voltages typically as low as 0.8V, with a guaranteed maximum
of 1V, and will operate down to 0.4V once the converter is operating, maxi-
mizing battery utilization.
Demanding applications such as Pagers and PDA’s require high efficiency
from several milli-watts to several hundred milli-watts, and the UCC3941
family accommodates these applications with >80% typical efficiencies
over the wide range of operation. The high efficiency at low output current
is achieved by optimizing switching and conduction losses along with low
quiescent current. At higher output current the 0.25Ω switch, and 0.4Ω syn-
chronous rectifier, along with continuous mode conduction, provide high ef-
ficiency. The wide input voltage range on the UCC3941 family can
accommodate other power sources such as NiCd and NiMH.
Other features include maximum power control and shutdown control.
Packages available are the 8-pin SOIC (D) and 8-pin DIP (N or J).
SIMPLIFIED BLOCK DIAGRAM AND APPLICATION CIRCUIT
10µF
22µH
+ 0.8V TO VOUT +0.5V
8V
VGD
2
10µF
VIN
3
STARTUP
CIRCUITRY
SW
8
0.4Ω
0.25Ω
OPEN=SD
MODULATOR CONTROL CIRCUIT
SYNCHRONOUS RECTIFICATION CIRCUITRY
ANTI-CROSS CONDUCTION
STARTUP
MULTIPLEXING LOGIC
MAXIMUM INPUT POWER CONTROL
ADAPTIVE CURRENT CONTROL
SD
4
UCC3941-ADJ
–
+ 1.25V
*FOR UCC3941-ADJ ONLY:
PIN 7 = SGND & PGND, PIN 6 = OUTPUT SENSE FEEDBACK, FB.
SLUS242 - JULY 1999
UCC3941-3 = 3.3V
UCC3941-5 = 5.0V
UCC3941-ADJ = 1.30V TO 6V
VOUT
1
100µF
PLIM
5
*SGND/FB
6
PGND
7
UDG-98147
|
| |
 
APPLICATION INFORMATION (cont.)
UCC2941-3/-5/-ADJ
UCC3941-3/-5/-ADJ
Figure 2. Inductor current and output ripple waveforms.
UDG-96117
At time t1, the 3.3V output drops below its lower thresh-
old, and the inductor is charged with an on time deter-
mined by:
12 µ s
TON = VIN
For a 1.25V input, and a 22µH inductor, the resulting
peak current is approximately 500mA. At time t2, the in-
ductor begins to discharge with a minimum off time of
1.7µs. Under lightly loaded conditions, the amount of en-
ergy delivered in this single pulse would satisfy the volt-
age control loop, and the converter would not command
any more energy pulses until the output again drops be-
low the lower voltage threshold.
At time t3, the VGD supply has dropped below its lower
threshold, but the output voltage is still above its thresh-
old point. This results in an energy pulse to the gate drive
supply at t4. However, while the gate drive is being serv-
iced, the output voltage has dropped below its lower
threshold, so the state machine commands an energy
pulse to the output as soon as the gate drive pulse is
completed.
Time t6, represents a transition between light and heavy
load. A single energy pulse is not sufficient to force the
output voltage above its upper threshold before the mini-
mum off time has expired, and a second charge cycle is
commanded. Since the inductor current does not reach
zero in this case, the peak current is greater than 0.5A at
the end of the next charge on time. The result is a
ratcheting of inductor current until either the output volt-
age is satisfied, or the converter reaches its programmed
current limit. At time t7, the gate drive voltage has
dropped below its threshold but the converter continues
to service the output because it has highest priority, un-
less VGD drops below 7.5V.
Between t7 and t8, the converter reaches its peak current
limit which is determined by RPL and VIN. Once the limit
is reached, the converter operates in continuous mode
with approximately 200mA of ripple current. At time t8,
the output voltage is satisfied, and the converter can ser-
vice VGD, which occurs at t9.
5
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| Information | Total 11 Pages | |
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| Download | [ UCC3941-5.PDF Datasheet ] | |
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